Patent Application
20210343368
The invention relates to methods for generating cell-type specific expression cassettes and reporter vectors, as well as nucleic acid constructs that can be generated by such methods. The cell-type specific expression cassettes and reporter vectors are characterized synthetic cis-regulatory DNA, also termed synthetic locus regions (sLCRs). sLCRs allow for a cell-type specific expression of reporter or effector genes. The invention further relates to various uses of the reporter vectors, including the determination of a property of a cell, preferably a cell type, state or fate transition, in gene and viral therapy, drug discovery or validation.
Expression cassettes and reporter vectors have a wide range of applications in basic research, drug screening diagnosis or gene therapy.
Selectively identifying cell type-specific identities is essential for understanding biological processes in which a diverse set of cell types contributes to tissue homeostasis. Ideally, this approach would also be informative in disease settings involving alterations in tissue homeostasis including metabolic, immunological, neurological or psychiatric disorders as well as inflammation and cancer. In developmental settings, this is traditionally achieved using lineage tracing1.
Among the most well-known examples, lineage tracing of Fbx15 expression led to the discovery of defined factors capable of reprogramming fibroblasts into pluripotent cells49, and lineage tracing of Lgr5 expression enabled the identification of bona fine colon and small intestine stem cells2, which was later shown to mark several other adult tissue stem cells3. The parallel development of sophisticated reporter strategies allows for single-cell resolution in analyzing multiple lineages.
Traditionally, several genetic tracing approaches have been exploited to generate reporter mice for cell-type specific genetic manipulation and cell labeling (e.g. LacZ, mGmT, Brainbow and Confetti systems, Mosaic Analysis with Double Markers—MADM, etc.). These strategies can reveal complex neuronal connection patterns4 and tackle outstanding questions such as the cell of origin for a tumor in a living organism5. More recently, Optogenetics and CRISRP/Cas9 based strategies added further flexibility in obtaining more quantitative readouts.
The use of reporter strategies based on adult stem cell biology can simultaneously inform on the origin of a tissue and it's aberrant homeostasis6 7 8. Genetic reporters reflecting well characterized pathways can lead to a deeper understanding of complex signaling dichotomy such as transforming growth factor counteracting bone morphogenetic protein (BMP) signaling during hair follicle homeostasis9.
In cancer, this approach critically revealed that aberrant homeostasis can be causal to therapy resistance10 or that a regeneration potential and tumor susceptibility may be shared among some organs, or markedly different in others11. Quantitative spatiotemporal patterning dynamics can be revealed by designing synthetic reporters based on transcription factor binding sites47. As inferred from these and several other studies, the choice of the genetic reporter is a critical factor for conclusively addressing sophisticated and complex biological questions. This is particularly valid in development or disease settings governed by multiple factors and complex interactions12.
In these settings, the ability to flexibly design synthetic reporters that intercept multiple pathways in a single genetic cassette will certainly prove to be a major asset, however current approaches are still limited.
For example, presently employed approaches for genetic tracing vectors rely on the use of cell-type, pathway specific or synthetic promoters or enhancers that are coupled to a reporter gene or a functional effector.
The use of cell-type-specific promoters is based on placing the reporter gene or functional effector after the minimal promoter of a signature gene of the cell-type of interest. It allows thereby for the specific transcriptional activation of a given reporter or effector as mediated the promoter for the given gene. Cell-type-specific vectors offer the possibility to use one given gene as a proxy of a cell state or developmental stage.
One example is the use of the Nestin promoter in order to mark neural progenitor cells. This approach is widely used and allows researchers to direct the activation of specific reporters or effectors in undifferentiated cells.
Significant limitations to these approaches are the necessity of prior knowledge on the signature genes and the assumption that regulatory elements for said genes are known and in close proximity to the transcriptional start site. Furthermore, the approaches suffer from an insufficient specificity of a single gene to depict complex regulatory systems. A cumbersome solution to this problem entails the cell type-specific identification of all the specific enhancers for any given cell type of interest followed by the selection of one of such elements and its cloning upstream a minimal viral promoter. This approach however is technically demanding and does rely on a supervised selection48. Both limitations do confine the application of such approach to very selected settings.
Alternative approaches use pathway-specific promoters in order to place the reporter or effector after artificially assembled transcription factor binding sites specific for a given pathway. Thereby specific transcriptional activation can be controlled through the mediation of regulatory elements known to be essential for said pathway.
One example is the BMP response element (BRE) specific for nuclear activity of SMAD1/5/8, which portrays the activation of the BMP pathway. While the BMP response element (BRE) reliably portrays the canonical pathway activation, it misses non-canonical activation and provides a reporter system which is insufficiently sensitive to feedback loops.
Limitations of using pathway-specific promoters include the need to rely on the assumption that the minimal set of regulatory elements used is sufficient to inform on the pathway activation. Furthermore a priori knowledge of such regulatory elements and their extensive characterization and isolation from their natural context is necessary and hamper their application for complex and less characterized cell types.
As a further approach synthetic enhancers or promoters have been proposed by placing the reporter of interest after multiple artificially assembled transcription factor binding sites before a minimal promoter. These methods also rely however on a priori knowledge of transcription factor binding sites known to be relevant for the cell type or developmental stage.
All methods suffer from their dependence on a priori knowledge or accurate discovery and validation of regulatory elements specific for the cell type or stage of interest. Furthermore, since in many cases not all regulatory elements are covered, multiple markers have to be used in order to ensure a reliable cell-type characterization, thereby complicating construction of the reporters and assessment of any experimental outcome.
The characterization of cells based upon the expression of cell-specific surface molecules via flow cytometry has also been described in the art. This is a common practice but limited in the sense that the corresponding markers have to be known in advance and not all cell types possess characteristic surface proteins. Furthermore, in vivo tracing of cell types is not possible or very challenging using such approaches.
Alternative gene expression reporter vectors have been developed in an attempt to employ multiple transcription factor binding sites to regulate expression of a reporter gene.
WO2001/49868 A1 (Korea Research Institute of Bioscience and Biotechnology) discloses a cancer-specific gene expression vector comprising a promoter with a binding site (EF2bs) for the E2F transcription factor expressed in cancerous genes as well as additional binding sites for further transcription factors (e.g. SP1, AP1, NF1 or C/EFB). This approach still however relies on a priori knowledge of TF binding sites (e.g. EF2bs) previously identified as being relevant in specific types of cancer.
WO 2015/110449 A1 (Universiteit Bruxelles/Gent) discloses a computational method for identifying cardiac and skeletal muscle specific regulatory elements with an enrichment of transcription factor binding sites (TFBS), wherein different regulatory regions (CSk-SH1-6; Sk-SH1) of a length of 300-500 bp are disclosed that each contain multiple (3-10) conserved TFBS. This technology focuses however on employing evolutionary conserved TFBSs, thereby relying on genomic conservation of the regulatory sequences, in order to enhance expression in muscle.
WO 2008/107725 A1 discloses a computational method for identifying transcription factor regulatory elements (TFREs) active in a cell of interest, wherein the TFREs have a length of at least 6 to 100 bp, wherein 6 or more TFREs may be combined in a promotor element of an expression vector. This technology employs however the fusion of the same pre-selected minimal promoter, with additional TFREs identified under any given conditions, i.e. the supervised merging of cis-elements with known function.
Guo et al. (Trends in Mol. Medicine, 14:410-418) review several viral vectors as well as transcriptional regulatory elements. Gargiulo et al. (Mechanisms of Development, 35:193-203) disclose the identification of cis-acting elements for a cell-specific expression of a vitelline membrane protein gene 32 (VMPE) in the follicular epithelium of Drospholia, wherein the expression vectors comprise different segments of the regulatory genomic regions.
Despite these advances in the field, such alternative approaches rely on disadvantageous strategies towards generating reporter vectors, such as a dependence on a priori knowledge of relevant promoters, a focus on genetic/evolutionary conservation of TFBSs, or the use of a single promoter which is modified by cis-elements with known function.
There is therefore a need in the field of synthetic reporters for alternative or improved methods and constructs based on non-biased de novo approaches for decoding and reconstructing regulatory information for any given cell type or state.
In light of the prior art the technical problem underlying the present invention is to provide alternative and/or improved means for the generation of genetic tracing cassettes or vectors based on synthetic cis-regulatory DNA that allow for a cell-type or developmental stage specific expression of reporter genes or functional effectors.
The problem is solved by the features of the independent claims. Preferred embodiments of the present invention are provided by the dependent claims.
The invention therefore relates to a method for generating a cell-type specific expression cassette, comprising the steps of:
The method allows for the generation of expression cassettes, which when introduced into a cell of interest yield expression of the reporter or effector gene in a manner highly specific to the particular entity or state, such as a cell type or state, which the reporter has been designed to depict, without the need of prior knowledge on the regulation of the gene expression in said entity or state of interest.
In contrast to the prior art, the method and constructs of the present invention are based on non-biased de novo approaches for decoding and reconstructing regulatory information for any given cell-type/state. The invention represents an entirely novel approach based essentially on the clustering of cell-type/state specific TFBSs at cell-type/state specific signature genes. The invention is also characterized by the advantages of employing a quantitative and/or statistical enrichment of relevant TFBS for any given cell-type/state.
In some embodiments the method essentially employs a systems biology approach to generate an expression cassette by identifying a set of endogenously occurring cis-regulatory elements from a given transcriptional signature of the cell type of interest and placing these cis-regulatory before a reporter or effector gene. This approach is independent of pre-conceived information on particular characteristics of the cell type of interest, thereby allowing standardized, unbiased and straightforward production of reporter constructs for any given cell type.
To this end the method identifies genomic sub-regions that comprise transcription factor binding sites characteristic for the cell type and assembles them into a set of genomic sub-regions that comprises a relevant portion of transcriptional regulatory sequence information within the cell type of interest. The set of genomic sub-regions may also be referred to as a “synthetic cis-regulatory DNA”, “synthetic regulatory region” or “synthetic locus control region (sLCR)”.
When introduced into a cell, the expression of the reporter or effector gene will occur, since in said cell type the transcription factors corresponding to the characteristic transcription factor binding sites are present and initiate expression of the reporter or effector gene. The level of expression is thus related to the particular cell type. Each cell type will essentially yield a different set of genes according to the signature gene set and each cell type will show differing levels of reporter expression depending on the transcription factors present and the combination of regulatory regions assembled in the sLCR.
Advantageously, the method is not limited to certain cell types, but may be applied to virtually any cell type and even distinguish cell state or fate transition within a certain cell type. To this end no a priori knowledge of gene regulation in the cell type of interest is needed.
Instead, the method only relies on the provision of a gene expression profile and genomic sequence data for a given cell type, which can be obtained using standard biomolecular techniques or consulting public databases.
The gene expression profile reflects the levels of gene expression within a cell type of interest. To this end for instance RNA-SEQ or other sequencing or microarray-based techniques can be used to quantify the levels of RNA transcripts with in the cell type of interest. However, the gene expression profile may also be potentially deduced using proteomics, e.g. by quantifying the expressed proteins or peptides present in the cell type of interest, which can be squared to the gene expression profile.
From the gene expression profile, signature genes are selected that are characteristic for the cell type, cell state or entity of interest. The selection of the signature genes can be adapted to the desired application.
For instance, signature genes may be selected according to their gene expression level, by ranking the genes of the cell type of interest according to their gene expression level and selecting genes that are above or below a certain threshold or selecting a predetermined number of highest or lowest expressed genes. For such a selection of signature genes the absolute expression levels of the genes of the cell type of interest serve as a reference. The resulting expression cassette may thereby faithfully report on the presence of the cell type of interest in various assays, independent of the cells to be probed.
However, for certain applications it may be desirable to generate an expression cassette that distinguishes the cell type of interest from a reference cell or a reference cell state with a particular high specificity. For such applications the differentially regulated signature genes are selected by identifying genes that are up- or down-regulated compared to the expression levels in the reference cell type. In these embodiments a gene expression profile of the cell type of interest and a reference cell type is provided. By selecting the differentially regulated genes the expression cassette can be fine-tuned for assays that need to distinguish a cell type (or state or fate) of interest to a certain reference type (or state or fate).
From the selected signatures genes, all genes encoding a transcription factor within the set of signature genes are identified. To this end the method may rely upon publically accessible annotated databases such as ENCODE, mENCODE (the mouse version of the ENCODE project), JASPAR, Ensemble, Entrez Gene, Genebank etc. Thereby a set of transcription factors for the cell type of interest is identified that is characteristically expressed. Transcription factors are identifiable by a skilled person through annotations of function in commonly available databases. Furthermore, the target sequences, ie transcription factor binding sites, for each transcription factor are typically known to a skilled person and/or are obtainable using appropriately annotated databases such as those described above. Preferably, in some embodiments, the method is directed towards the use of transcription factors for which their binding sites (in the form of DNA sequences or sequence motifs) are already known and/or preferably annotated in public databases.
Furthermore, the set of selected genes is used to determine a set of genomic regions from the genomic sequence data of the cell type of interest, wherein each genomic region comprises a sequence encoding a signature gene and additional genomic sequence adjacent to (preferably immediately flanking) the sequence encoding said signature gene. This genomic sequence, e.g. non-coding reference DNA (although cis-regulatory elements may be presented in coding regions), is intended to encompass regulatory sequences, which can be positioned upstream, downstream of, or within coding regions, more often in close proximity to a transcriptional start site but not exclusively there. The size of the additional genomic sequence adjacent to the signature gene may vary as the method is advantageously not overly sensitive to the presence of extra portions of additional genomic sequence.
Thus, the additional genomic sequence should be large enough to encompass cis-regulatory elements (in particular transcription factor binding sites, or enhancers or silencers) that regulate the expression of the signature gene. It is known that such cis-regulatory elements may be in close proximity to the coding region structurally, but—given the 3D structural distribution of the genome in the nucleolus—the cis-regulatory elements may be located at a significant distance in terms of the linear genome sequence. In preferred embodiments, the regulatory genomic sequence is chosen based upon the folded three-dimensional state of the DNA within chromatin in the cell type by using topological associating domains as boundaries. Preferably, in some embodiments, the method assumes cell-type specific non-coding CTCF binding sites as proxy for topological associating domains. CTCF binding sites (in the form of DNA sequences or sequence motifs) are typically known to a skilled person and/or typically annotated in public databases.
In preferred embodiments, after determining the set of genomic regions, the method searches for multiple genomic sub-regions of similar or comparable size (e.g. equal size) that comprise one or more, preferably several, binding sites for the transcription factors that are encoded by the signature genes. All of the genomic sub-regions identified in step f) of the method thus comprise a DNA binding sites for a transcription factor that is characteristically expressed in the cell type of interest. When the genomic sub-region is assembled in a sLCR and said sLCRs is introduced into the cell of interest the characteristically expressed signature transcription factors may bind to said sLCR and regulate the expression of a downstream reporter or effector gene. Typically, a number of genomic sub-regions larger than the ones composing the sLCR are identified, which are redundant in terms of the binding sites for the characteristic transcription factors. An assembly of a limited number of all identified genomic sub-regions is sufficient to represent the overall regulatory complexity and including all elements would not result in increased specificity but rather in unnecessarily large expression cassettes.
The method therefore further encompasses a step to select a minimal set of genomic sub-regions comprising transcription factor binding sites for a predetermined percentage of all transcription factors encoded by the selected signature genes.
By way of example, one can assume within the set of signature genes 100 transcription factors may be identified for which 100 transcription factor binding sites are known. In some embodiments, however, the number of transcription factors encoded by the selected signature genes does not necessarily equal the number of transcription factor binding sites. In some selected embodiments, not all the transcription factors may have known binding sites or multiple transcription factor binding sites matrices may be associated to some transcription factors.
In the quest for the lower possible number of genomic sub-regions to be used in the assembly of a sLCR, e.g. to keep the resulting regulatory sequence compact, the method then preferably ranks the genomic sub-regions according to the number of transcription factor binding sites, in addition to the diversity of the transcription factor binding sites. For instance, the highest ranked genomic sub-region may contain 35 transcription factor binding sites for the transcription factors of step d), wherein 3 of these binding sites are represented 5 times in the same genomic sub-region, while the remaining binding sites are present only once. This highest ranked genomic sub-region would then comprise 23 different (unique) transcription factor binding sites which represent binding sites for 23 transcription factors of the signature genes. This highest ranked genomic sub-region would thus cover 23% of the characteristic transcription factors of step d).
If for instance the predetermined percentage is set to 50%, a second (and potentially third) genomic sub-region(s) would be searched for that encompasses preferably transcription factor binding sites not yet contained within the 23 binding sites of the first genomic sub-region, and so on, such that the further genomic sub-region(s) would comprise at least 7 binding sites for transcription factors not already covered by the first, most highly ranked, genomic sub-region. Typically, a minimal set of 2-10 genomic sub-regions will comprise transcription factor binding sites that are binding targets for at least 50% of the transcription factors encoded by the signature genes.
When the expression cassette is introduced into the cell type of interest, the minimal set of genomic sub-regions act as a synthetic cis-regulatory DNA to which the characteristic transcription factors can bind. The minimal set of genomic sub-regions selected in step g) of the method is therefore herein therefore referred to as a synthetic locus control region (sLCR). In some embodiments, the cassette therefore comprises a regulatory region (sLCR) enriched for regulatory sequences that are bound by transcription factors that are e.g. expressed or highly expressed in the cell type of interest. This regulatory region is therefore unique/tailored to this particular cell type and lead to an expression level of the reporter gene unique to this cell type.
Considering the total amount of characteristic transcription factors identified in d) reflects the regulatory machinery of the cell type of interest, the predetermined percentage of coverage of transcription factors can be regarded as a “percentage of regulatory information” that is covered by the minimal set of genomic sub-regions. Theoretically, the higher the amount of regulatory information covered, the more specific the expression of the reporter or effector gene will be to the cell type. However, advantageously, a percentage covering at least 30% of regulatory information, preferably at least 40% or 50% yields excellent results in terms of a cell-type specific expression profile, as gauged by experimental validation.
In step h) of the method, a cell-type specific expression cassette is generated by assembling the set minimal of genomic sub-regions selected in step g) with a reporter or effector such that they are operably coupled, i.e. that the genomic sub-regions comprising the transcription factor binding sites as cis-regulatory elements are configured to regulate the expression of the reporter or effector gene.
The high coverage of regulatory information by means of the assembled genomic sub-regions without the need of prior information opens a vast potential of application for the methods and constructs described herein. The expression cassettes, as a part of a reporter vector, may be exploited in vitro and in vivo as a reporter for intrinsic cell states, for adaptive responses to external signaling or chemical inputs, cell fate transitions, reprogramming, forward and chemical genetic screenings. Furthermore when the cell-type specific sLCR are combined with endonucleases or suicide genes, the vectors can be used to deplete cell-type, developmental-stage or disease-specific populations in gene therapy or other genetic modification settings. Among these other genetic modification settings, sLCRs may drive the tumor-specific expression of structural components of an oncolytic virus and/or co-stimulatory molecules aiming at increasing the specificity and effectiveness of an oncolytic therapy.
In a preferred embodiment of the invention the method is characterized in that the gene expression profile comprises expression levels of genes in the cell type of interest, and
The second alternative allows for the selection of signature genes based upon a comparison of the expression level of the genes of said cell type as derivable from the gene expression profile. Such an embodiment is particularly well suited for the generation of expression cassettes that will represent the cell type of interest in different experimental settings. To this end the selection of the genes that are 3- to 10-fold or more upregulated than the average expression level have yielded excellent results.
The first alternative allows for tailoring of the expression cassette to distinguish a cell type of interest compared to a reference cell type. By way of example, the cell type of interest may be a certain tumor cell, while the reference cell type refers to a normal cell of the tissue type typically invaded by the tumor, or by the cell type from which the tumor cell originated.
The reference cell type may however also refer to the same type cell, but in a different cell state or before or after a fate transition. The gene expression profile of the cell type of interest may refer to the gene expression profile of a cancer cell in a mesenchymal state after an epithelial-to-mesenchymal transition (EMT), whereas the gene expression profile of the reference cell type may refer to the gene expression profile of the same type of cancer cell, but in its epithelial state, i.e. before epithelial-to-mesenchymal transition (ETM). In this case the expression cassette will be able to distinguish cells that have undergone EMT from those that did not.
Expression cassettes derivable by selecting the signature genes based upon a relative regulation in comparison to reference cell types are characterized by particularly high specificity allowing for a distinction of the reference cell type from the cell type of interest without the need of any additional marker.
In a preferred embodiment of the invention the method is characterized in that the predetermined percentage of transcription factors covered is 30% or more, preferably 40% or more, most preferably 50%, or more.
In a further preferred embodiment of the invention the method is characterized in that the genomic regions determined in e) correspond to genomic sequences of topological associating domains that contain the differentially regulated gene, wherein preferably a topological associating domain corresponds to a genomic sequence between two CTFC-binding sites.
By selecting the size of the genomic region based upon the topological associating domains an optimal coverage of the potential cis-regulatory elements governing the transcription of said signature genes can be achieved. Within a topological associating domain DNA sequences physically interact with each other more frequently than with sequences outside the topological associating domain, thereby forming a three-dimensional chromosome structures accessible for the transcriptional machinery. Particularly good results could be achieved by selecting genomic sequence between two CTFC-binding sites. Such embodiment yields an optimal balance between computational power resources, specificity of the non-coding cis-regulatory DNA to the genes they are most likely regulating and the size of the flanking DNA to cover the characteristic transcription factor binding sites.
In a preferred embodiment of the method the identification of genomic sub-regions of comparable, e.g. equal, size in step f) is performed by a sliding window algorithm of the genomic regions determined in e), wherein preferably the window has a length of 500 bp to 5000 bp, preferably 700 bp to 2000 bp, more preferably 800 bp to 1200 bp, most preferably 1000 bp and the sliding step has a length of 100 bp to 1000 bp, preferably 120 bp to 300 bp, more preferably 130 bp to 170 bp, most preferably 150 bp. In one embodiment the sliding window is fixed to 1000 bp in size sliding by 150 bp steps, although the genomic sub-regions size resulting out of the scanning may vary in size because it depends on the statistical score and distribution of the TFBS.
It is further preferred that the sliding window algorithm calculates the statistical enrichment of the transcription factor binding sites motifs from a relevant data base (e.g. JASPAR) restricted to the transcription factor bindings sites corresponding to the transcription factors identified in step d). Hereby a list of significant enrichment of characteristic transcription factor binding sites within specific regions is generated and used to identify genomic sub-regions of comparable, preferably equal, size that comprise at least one transcription factor binding site for at least one characteristic transcription factor encoded by a signature gene. Preferably and most likely, tens (10 to 200, preferably between 20 and 180) of TFBS are comprised within genomic sub-regions of comparable size.
According to the present invention, the multiple genomic sub-regions of comparable and limited size, preferably equal size, within the set of genomic regions determined in e) (according to step f), are typically the same size but may vary. Comparable in this context refers to multiple genomic sub-regions that exhibit preferably any window size of 500 bp to 5000 bp.
In a further preferred embodiment of the invention the genomic sub-regions have a length of 100 bp to 1000 bp, preferably 120 bp to 300 bp, more preferably 130 bp to 170 bp, most preferably 150 bp. If a sliding window algorithm is used, the length of the genomic sub-regions will preferably correlate with the sliding step. In other embodiments, the sliding window approach may use any given step size, from 1 bp up to those step sizes indicated for the window sizes above. The preferred length have been determined by employing the method to difference cell types and assay system and reflect the optimal results in terms of expression specificity and total size of the expression cassette.
In a further preferred embodiment of the invention the method is characterized in that the selection of a set of genomic sub-regions in g) is performed by calculating for each genomic sub-region identified in f):
For instance, the number and type of transcription factor binding sites have been generated after identifying genes encoding a transcription factor within the set of signature genes selected in c). Furthermore a list of genomic sub-regions generated in step f) is provided. With this information, one may calculate the number of transcription factor binding sites (TFBS) per genomic sub-region (e.g. TFBS=35) representing the enrichment for binding sites of the transcription factors according to d) in the genomic sequence data. Furthermore it is preferred that the diversity of transcription factor binding sites per genomic sub-region is calculated. For instance, among the 35 TFBS 3 TFBS may be present 5 times, while the remaining TFBS are only present once yielding for said genomic sub-region a number of 35 TFBS with a diversity score of 23.
In a further step the preferred method will rank the genomic sub-regions based upon the highest number of TFBS and the best diversity score. As an example of a number one ranking, in the genomic locus chr10:6019558-6019708, there are 20 TFBS that the said method associated with a Mesenchymal GBM state, with some repeated 2 to 6 times. Once the best ranked genomic sub-region is determined one may calculate the second best in all the remaining genomic sub-regions, wherein TFBS present in the first genomic sub-region are excluded from the ranking. By iteration one may calculate how many different genomic sub-regions are required to cover the entire set of transcription factor binding sites or a predetermined percentage. When a percentage of all regulatory potential (TFBSn×TFBSd) is needed, two independents LCRs may be generated. Typically 4-5 elements are sufficient to reach up to 50% of the regulatory potential, and this was validated as sufficient to generate two independent sLCRs responding to the same signaling (see Examples).
In a further preferred embodiment of the invention, the method is characterized in that the configuration of genomic sub-regions in h) is such that genomic sub-regions comprising a transcription start site are assembled adjacent and upstream of the sequence encoding the reporter gene and the genomic sub-regions not comprising a transcription start site are preferably assembled further upstream from the closest transcription start site. In this case it is particularly preferred that the method may annotate all the genomic sub-regions elements (e.g. 150 bp elements) that contain a natural transcription start site and those which do not and the ranking will start from the transcription start site-containing genomic sub-regions. After the best ranked genomic sub-regions containing a transcriptional starting site is chosen, the ranking of additional genomic sub-region may be performed independent of whether those genomic sub-regions contain a transcription starting site or not.
According to the present invention, in some embodiments, the term “generating a cell-type specific expression cassette” relates to the design and physical production of a nucleic acid molecule. In some embodiments, the term “generating a cell-type specific expression cassette” relates to the design of a cell-type specific expression cassette without physically producing the corresponding nucleic acid molecule, for example the method may be a computer-implemented method or may comprise one or more computer-implemented steps in the method. In some embodiments the method is or comprises computer-implemented elements and produces, as the output of the method, an in silico design, product, simulation and/or computer representation of said construct. The “generating” of a cassette or construct may therefore in some embodiments occur in the computer, ie in computer software, for example the output may be a nucleic acid sequence, nucleic acid sequence information, ie in computer readable format.
The method of the present invention, in some embodiments, may also relate to a computer programme product, such as a software product.
The software may be configured for execution on common computing devices and is configured for carrying out one or more of the steps a) to h) of the method described herein. The computer programme product of the present invention therefore also encompasses and directly relates to the features as described for the method provided herein. Further details on preferred computer-based approaches are provided in the examples and relevant references as described herein. If the method is carried out in a computer programme, for example by way of simulation or computer design of an inventive cassette, the sequence may, in some embodiments, be subsequently synthesized by methods known to a skilled person in a laboratory and utilized in which ever in vitro or in vivo application is desired.
The invention also relates to a system for carrying out the method described herein, comprising one or more computing devices, data storage devices and/or software as system components, wherein said components may be preferably connected in close proximity to one another or via a data connection, for example over the internet, and are configured to interact with one or more of said components and/or to carry out the method described herein. The system may comprise computing devices, data storage devices and/or appropriate software, for example individual software modules, which interact with each other to carry out the method as described herein.
Regarding Computer Implementation:
Step a) regarding providing a gene expression profile of a cell type of interest, may be computer implemented, ie the information for a gene expression profile of a cell type of interest is preferably presented in a computer readable format, configured for processing in the further steps of the method.
Step b) regarding providing genomic sequence data of said cell type of interest, may be computer implemented, ie the information for genomic sequence data is preferably presented in a computer readable format, configured for processing in the further steps of the method.
Step c), regarding selecting a set of signature genes from the gene expression profile, wherein said signature genes are (i) differentially regulated compared to a reference cell type or (ii) selected according to a gene expression level, is preferably computer-implemented. In preferred embodiments genes and their expression profiles are represented as information in a format configured for processing by a computing device, such that a particular group of genes can be selected based on this information. This step may be automated or performed manually, depending on the selection characteristics employed/needed or skills of the user.
Step d), regarding identifying genes encoding a transcription factor within the set of signature genes selected in c), is preferably carried out in a computer implemented method, whereby the genes are annotated with function, such that a transcription factor function can be (optionally) automatically interrogated in any one or more of the identified signature genes. Appropriate databases may be employed, as mentioned by way of example herein.
Step e) regarding determining a set of genomic regions from the genomic sequence data, wherein each genomic region comprises a sequence encoding a signature gene identified in c) and additional genomic sequence adjacent to the sequence encoding said signature gene, is preferably carried out in a computer implemented method. Assessing and selecting genomic sequence adjacent to genes of interest can be carried out by a skilled person based on genomic sequence, ie as available from databases, either by using automatic selection criteria, or by manually assessing and selecting adjacent sequence.
Step f), regarding identifying multiple genomic sub-regions of equal size within the set of genomic regions determined in e), wherein said genomic sub-regions comprise one or more binding sites for one or more of the transcription factors identified in d), is preferably carried out using computer implemented methods. The identification of binding sites for one or more of the transcription factors can be carried out using methods established in the art, for example any given sequence is searched and/or interrogated for the presence of known binding sites, defined by particular sequences or sequence motifs. Software configured for screening sequences for the presence of such known sequences is available to a skilled person.
Step g), regarding selecting a minimal set of genomic sub-regions, preferably between 2 and 10, from those determined in f), wherein the set of genomic sub-regions is selected to comprise transcription factor binding sites for a predetermined percentage of all transcription factors identified in d), is preferably carried out using a (optionally) automated computer algorithm. Details on the determination of genomic sub-regions is provided above. Multiple options are available for software solutions suitable for selecting the desired genomic sub-regions, or the selection can be carried out manually by the skilled user assessing the various sub-regions and compiling them to comprise binding sites for a certain percentage of the relevant transcription factors identified in step d).
Software can be designed and/or configured by a skilled person using established programming, coding, and bioinformatic techniques to assess genomic sub-regions for the presence of transcription factor binding sites, comparison of these binding sites to the transcription factors identified as signature genes, and selecting a compilation of genomic sub-regions to cover a predetermined percentage of the relevant transcription factors.
According to step h) of the method a cell-type specific expression cassette, comprising the set of genomic sub-regions selected in step g) operably coupled with a reporter or effector gene, is generated. As described above, said “generating” may relate to the computer implemented production of nucleic acid sequence information in computer readable form and/or to the synthesis of a physical nucleic acid molecule based on and/or comprising said sequence.
The invention therefore further relates to a method for designing and/or manufacturing a nucleic acid molecule that corresponds, comprises or is based on the product DNA sequence information obtained from steps a) to g). The method preferably comprises comprising carrying out the method described herein and subsequently synthesizing, cloning and/or isolating said nucleic acid molecule.
The term “generating a cassette” may in such embodiments comprise any relevant molecular biological or chemical technique for cloning, mutation, recombination, PCR amplification and/or synthesis used in generating a nucleic acid molecule.
In preferred embodiments the cassette is synthesized using de novo nucleic acid synthesis based on the information obtained by the method of the invention.
In a further preferred embodiment, the invention relates to a cell-type specific reporter vector including an expression cassette generated by a method as described herein.
In a further aspect, the invention relates cell-type specific reporter vector, comprising a synthetic regulatory region comprising 2 to 10 genomic sub-regions of 100 bp to 1000 bp, positioned adjacently, without a linker or with a linker sequence of or less than 100 bp positioned between said sub-regions, wherein said sub-regions originate from separate (non-adjacent) locations in the same genome of a cell type of interest, wherein the sub-regions cumulatively comprise binding sites for at least 5, preferably at least 10, most preferably at least 20 transcription factors, and
a reporter or effector gene,
wherein the genomic sub-regions are operably coupled with a reporter or effector gene to regulate the expression of said reporter or effector gene.
It is particularly preferred that the genomic sub-regions are selected by a method according to the steps a) to g) as described herein. A person skilled in the art will appreciate that preferred embodiments disclosed for the method equally apply to the cell-type specific reporter vector described herein. The method of the invention leads to structural features of the vector, unique in this field.
A preferred embodiment of the invention relates to the construct design, where transcription factor binding sites from genomic subregions have a length of 100 to 1500 bp or 100 to 1250 bp, preferably 100 to 1000 bp, more preferably 120 bp to 300 bp, more preferably 130 bp to 170 bp, most preferably essentially 150 bp, combined with the origin of the genomic subregions from non-adjacent regions of the same genome. Through this combination, the constructs of the invention are defined by a novel de novo and non-biased construction, by pulling together distinct/separated but highly relevant regulatory regions, that reflect the relevant size of regulatory information, in particular for sizes of preferably 120 bp to 300 bp, more preferably 130 bp to 170 bp, most preferably 150 bp, which approximate the size of a histone particle upon which DNA is wrapped.
A preferred embodiment of the invention relates to the construct design, where 5 or more transcription factor binding sites are used, i.e. the higher numbers of TFBSs reflect a novel de novo and non-biased construction, by pulling together sufficient numbers of TFBSs to cover a large regulatory portion of relevant TFs in any given cell type/state.
The genomic sub-regions are characterized in that they originate from separate locations in the same genome of a cell type and cumulatively comprise binding sites for at least 5, preferably at least 10, most preferably at least 20, or more, transcription factors. In some embodiments, the 2-10 (i.e. 2, 3, 4, 5, 6, 7, 8, 9 or 10) genomic sub-regions are compiled to form a sLCR comprising at least 5, 10, 15, 20, 25, 30, 35, 40, or more, transcription factor binding sites. Thereby the genomic sub-regions cover binding sites for a large amount of transcription factors typically sufficient to cover the regulatory information of a cell type of interest. It is preferred that the binding sites for the transcription factors refer to transcription factors that characteristically expressed in the cell type of interest. To determine transcription factors that are characteristically expressed in the cell type of interest e.g. steps a) through d) of the method described herein may be employed.
Using synthetic regulatory regions comprising 2 to 10 of such genomic sub-regions with a length of 100 bp to 1000 bp have proven an optimal regime in terms of minimizing the size of the vector, while maintaining a high amount of regulatory information as represented by the transcription factor binding sites.
In this regard also the positioning the genomic sub-regions adjacently without a linker or with a linker sequence of less than 100 bp ensures a compact design of the reporter vector and an efficient transduction without comprising on the amount of regulatory information.
In a particular preferred embodiment of the invention the vector is characterized in that each of the genomic sub-regions has a length of 120 bp to 300 bp, more preferably 130 bp to 170 bp, most preferably 150 bp. Such lengths of the genomic sub-regions optimally cover the relevant transcription factor binding sites enriched with statistical significance over the background genomic regions. The optimal size of 150 bp may be due to the fact histones wrap around round 146 base pairs (bp) of the DNA genome around their core particles preventing access to transcription factors. In constrast, nucleosome free regions (NFRs) which are usually associated with active cis-regulatory DNA when upon unwrapping the DNA enables accessibility for transcription factors, which are therefore minimally 146pb. The average size of cis-regulatory DNA is generally inferred by the average size of NFRs—otherwise referred to as DNAsel hypersensitive sites—which is about 1000 bp and usually contains a clustering of relevant transcription factor binding sites on these length scales.
In a further preferred embodiment of the invention the vector is characterized in that the genomic sub-region adjacent to the reporter or effector gene comprises a transcription start site. This ensures that the effector and reporter are in frame and may positively be regulated by the upstream synthetic regulatory region.
The unique design of the invention described herein has the advantage that a variety of reporter or effector genes can be coupled to the synthetic regulatory region comprising the genomic sub-regions depending on the desired application.
In a preferred embodiment of the invention the vector is characterized in that the reporter or effector gene encodes a protein selected from a group comprising a fluorescent protein, a suicide gene, a luciferase, a β-galactosidase, a chloramphenicol acetyltransferase, a surface receptor, a protein tag, including but not limited to 6×His tag, V5 tag, GFP tag, a self-processing ribozyme cassette, a mevalonate kinase and derivates thereof, a biotin ligase and derivates thereof including but not limited to BirA, a engineered peroxidase and derivates thereof including but not limited to APEX2, an endonuclease or site-specific recombinase and derivates thereof, including but not limited to restriction enzymes, Cre, Flp, Tn5, SpCas9, SaCas9, TALENs, a gene correcting a monogenic disease, a viral antigen such as E1A and E1B to induce cell-type specific vaccination, or adjuvant cytockines/chemockines to enhance immune recognition, such as GM-CSF or IL-12.
Fluorescent proteins may be particularly useful for any kind of optical measurement of a signal indicative of the expression of the reporter gene. To this end the method may profit from using the state of the art microscopic and/or fluorescence-activated cell sorting devices and quantification techniques.
Furthermore, the invention can be readily employed using different kind of vector system and easily adapted to the cells of interests.
In a preferred embodiment of the invention the vector is a viral vector, preferably a lentiviral or Adeno-associated viral vector.
In a further preferred embodiment of the invention the vector comprises a nucleic acid sequence according to SEQ ID NO 1-6 or a nucleic acid sequence with an identity of at least 80%, preferably of at least 90%, to any one of SEQ ID NO 1-6.
As described herein the invention allows for the provision of cell-type specific vector construct that mediate a reliable expression of desired reporter or effector genes in the cell type of interest without the need of a prior knowledge. As such the vector construct allow for a variety of different application ranging from basic research to clinical studies or therapeutic strategies.
For instance the vector constructs can be used for the identification of a cell type or the determination of an intrinsic cell state or developmental state of cells. The vectors also allow to study how cells react to external signals or chemicals. Moreover, the vectors can be used in diagnostics, for example to determine the state or type of a cancer, e.g. whether an epithelial or mesenchymal glioblastoma is present and thereby allow for more effective therapeutic guidance. Furthermore, the vectors may also be employed as pharmaceutical agents themselves for instance in gene therapeutic approaches.
In a preferred embodiment the invention relates to the use of a vector for transforming a cell and/or determining a property of a cell, preferably a cell type, state or fate transition, for gene and viral therapy, drug discovery or validation.
The presence of a vector or sLCR as described herein inside an already-transformed cell, is covered in embodiments of the invention.
In one embodiment the invention relates to a method for determining a property of a cell, preferably a cell type, state or fate transition, comprising the steps of
Any suitable measurement technique may be employed. For instance the reporter or effector gene may be a fluorescent protein, in which case microscopic devices may be used to quantitatively assess the fluorescent signal and thereby the expression of the reporter or effector gene in the cells probed.
In one embodiment the invention relates to a method for determining an intrinsic cell state, comprising the steps of
In one embodiment the invention relates to a method for determining cell fate transitions, comprising the steps of
In one embodiment the invention relates to a method for determining cell fate reprogramming factors, comprising the steps of
In one embodiment the invention relates to a method for determining the minimal requirements for in vitro cellular propagation of an intended phenotype, comprising the steps of
In one embodiment the invention relates to a method for a targeted correction of diseased cells, comprising the steps of
In one embodiment the invention relates to a method for Oncolytic viral therapy, comprising a comprising the steps of:
The methods described herein, for example those for determining a property of a cell, preferably a cell type, state or fate transition, may be employed in various biological, biotechnological or pharmaceutical (screening) settings.
A further embodiment of the invention relates to using DNA methylation and/or ATAC-seq profiles as an input for signature genes discovery.
ATAC-seq (Assay for Transposase-Accessible Chromatin using sequencing) is a technique used to assess genome-wide chromatin accessibility by probing open chromatin with hyperactive mutant Tn5 transposase that inserts sequencing adapters into open regions of the genome. The mutant Tn5 transposase excises any sufficiently long DNA in a process called tagmentation, whereby the simultaneous fragmentation and tagging of DNA is performed by Tn5 transposase pre-loaded with sequencing adaptors. The tagged DNA fragments are then purified, amplified by PCR and sent for sequencing. Sequencing reads can then be used to infer regions of increased accessibility as well as to map regions of transcription-factor binding sites and nucleosome positions.
The chromatin accessibility of several classes of cis-regulatory elements is a predictive marker of in vivo DNA binding by transcription factors. The repertoire of all accessible sites in chromatin is the strongest predictor of cell identity. Indeed, in cancer, chromatin accessibility is the strongest predictor of cancer type similarity and can be used to identify subtype identities within the common dimensional space of individual cancer types. To investigate whether the acquired heterogeneity depicted by sLCRs is accompanied by changes in genome-wide chromatin accessibility, ATAC-seq can be performed cells sorted according to expression levels of the reporter constructs described herein. Differential analysis of chromatin accessibility can therefore uncover many genes undergoing remodeling. These results described in the examples below highlight the efficacy of sLCRs in revealing e.g. intra-tumoral heterogeneity and enabling in-depth cellular and molecular characterization of tumor models together with primary cancer data.
A further embodiment of the invention relates to target discovery and validation for drug targets in the area of stress responses (e.g. killing cells with high ER stress or inflammatory signaling) and senolitics (e.g. killing senescent cells).
Using the method of the present invention, specific regulatory profiles can be identified for any given cell state, and a reporter construct effectively generated. In some embodiments, a sLCR can be generated for a cell type/state with high ER stress, or inflammatory signaling, or undergoing senescence. Such a reporter can therefore be used to measure whether any given drug candidate, ie.e. applied during a screen, leads to change in the cell state.
A further embodiment of the invention relates to target discovery and validation for drug targets in the area of cell identity/fate changes. As described herein in detail, specific regulatory profiles can be identified for any given cell identity, or for states before and after identity or fate changes, and a reporter constructs effectively generated. In some embodiments, sLCRs can be generated for cell types before and after identity change. Such reporters can therefore be used to measure whether any given drug candidate, ie.e. applied during a screen, leads to change in the cell state.
A further embodiment of the invention relates to target discovery and validation for synthetic peptides, using the methods and constructs described herein.
A further embodiment of the invention relates to target discovery and validation for therapeutic exosomes and anti-sense oligonucleotides, using the methods and constructs described herein.
A further embodiment of the invention relates to discovery of therapeutic potential of drug candidates in immunotherapy, including but not limited to, the role for innate immune cells in therapeutic response and resistance, and the use of sLCRs to engineer therapeutic adaptive immune cells (T-cells, NK) to resist exhaustion and main target specificity.
In some embodiments sLCRs can be generated as a readout for immune cell activity and/or target specificity, and candidate molecules can be tested and changes in sLCR readout measured in order to assess if immune cells (T-cells, NK) can resist exhaustion when enhanced/treated with a candidate compound.
In a further embodiment the invention relates to a computer-implemented method for determining the sequence of a synthetic locus control region (sLCR), comprising the steps a) to g) of the method as described herein. The invention therefore also relates to computer software products capable and adapted to carry out the method steps a) through g) as described herein as well as a computer program for use in a methods described herein comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of a) to g) of the method described herein.
The present invention is directed a method for generating cell-type specific expression cassettes, cell-type specific vectors using such an expression cassette as well as application of such vectors. Before the present invention is described with regards to the examples, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
All cited documents of the patent and non-patent literature are hereby incorporated by reference in their entirety. All terms are to be given their ordinary technical meaning, unless otherwise described herein.
As used herein the term “expression cassette” refers to a nucleic acid construct comprising nucleic acid elements sufficient for the expression of a gene product. The expression cassette also encompasses an electronic representation of an expression cassette, as described herein. Typically, an expression cassette comprises a nucleic acid (sequence) encoding as a gene product a reporter gene or a functional effector operatively linked to the selected genomic sub-regions comprising transcriptional binding sites that act as regulatory elements for the expression of the gene product.
As used herein, the terms “synthetic cis-regulatory DNA”, “synthetic regulatory region” or “synthetic locus control region (sLCR)” refer to an arrangement of multiple genomic sub-regions that comprise validated and/or potential (putative/predicted) cis-regulatory sequences arranged adjacently (with or without a spacer) in a non-naturally occurring order (i.e. not occurring in that order or arrangement in a naturally occurring genome). Examples of cis regulatory sequences are transcription factor binding sites (TFBS), promoters, enhancers, silencers, or other regulatory sequence capable of acting in cis on the expression of a coding region. These regulatory regions, when arranged into a synthetic regulatory region, are typically characteristic for a cell type. The method described herein preferably assembles these regulatory regions into a set of genomic sub-regions that comprises a relevant portion of transcriptional regulatory sequence information within the cell type of interest.
As used herein the term “reporter vector” refers to a nucleic acid construct comprising an expression cassette and further nucleic acid elements that allow for introducing the expression cassette into cells either in vitro or in vivo. The term “reporter vector”, “vector” and “effector vector” may be used interchangeably. A “vector” can have one or more restriction endonuclease recognition sites (whether type I, II or IIs) at which the sequences can be cut in a determinable fashion without loss of an essential biological function of the vector, and into which a nucleic acid fragment can be spliced or inserted in order to bring about its replication and cloning. Vectors can also comprise one or more recombination sites that permit exchange of nucleic acid sequences between two nucleic acid molecules. Vectors can further provide primer sites, e.g., for PCR, transcriptional and/or translational initiation and/or regulation sites, recombinational signals, replicons, selectable markers, etc. A vector can further contain one or more selectable markers suitable for use in the identification of cells transformed with the vector. Vectors known in the art and those commercially available (and variants or derivatives thereof) can be used with the expression cassettes described herein. Such vectors can be obtained from, for example, Vector Laboratories Inc., Invitrogen, Promega, Novagen, NEB, Clontech, Boehringer Mannheim, Pharmacia, EpiCenter, OriGenes Technologies Inc., Stratagene, PerkinElmer, Pharmingen, and Research Genetics, or can be freely distributed among scientists through Addgene.
As used herein, the term “viral vector” refers to a nucleic acid vector construct that includes at least one element of viral origin and has the capacity to be packaged into a viral vector particle, encodes at least an exogenous nucleic acid. The vector and/or particle can be utilized for the purpose of transferring any nucleic acids into cells either in vitro or in vivo. Numerous forms of viral vectors are known in the art. The term virion is used to refer to a single infective viral particle. “Viral vector”, “viral vector particle” and “viral particle” also refer to a complete virus particle with its DNA or RNA core and protein coat as it exists outside the cell.
The term “transfection” refers preferably to the delivery of DNA into eukaryotic (e.g., mammalian) cells. The term “transformation” refers preferably to delivery of DNA into prokaryotic (e.g., E. coli) cells. The term “transduction” refers preferably to infecting cells with viral particles. The nucleic acid molecule can be stably integrated into the genome generally known in the art. The terms “transduction”, “transfection” and “transformation” may however be used interchangeably herein and refer to the process of introducing a vector comprising an expression cassette into a cell.
As used herein the term “cell-type specific” relates to the specificity of the expression of a reporter or effector gene, when an expression cassette as described-herein is introduced into a cell of interest in comparison to other (e.g. reference cells). The term cell-type specific encompasses an expression (level) specific to the cell type of the cell of interest as well as its cell state or fate. The term cell-type specific expression cassette or vector therefore encompasses as well cell-state specific as well as cell-fate specific expression cassette or vectors.
The terms “reporter”, “effector” or “reporter or effector gene”, as used herein, refer to gene products, encoded by a nucleic acid comprised in an expression construct as provided herein, that can be detected by an assay or method known in the art, thus “reporting” expression of the construct and/or “effecting” the state or fate of the cell they are expressed in. Reporters and effectors and nucleic acid sequences encoding reporters are well known in the art. Reporters or effectors include, for example, fluorescent proteins, such as green fluorescent protein (GFP), blue fluorescent protein (BFP), yellow fluorescent protein (YFP), red fluorescent protein (RFP), enhanced fluorescent protein derivatives (e.g. eGFP, eYFP, mVenus, eRFP, mCherry, etc.), enzymes (e.g. enzymes catalyzing a reaction yielding a detectable product, such as luciferases, beta-glucuronidases, chloramphenicol acetyltransferases, aminoglycoside phosphotransferases, aminocyclitol phosphotransferases, or puromycin N-acetyl-tranferases), and surface antigens. Appropriate reporters or effectors will be apparent to those of skill in the related arts. Preferred proteins are selected from a group comprising a fluorescent protein, a suicide gene including but not limited to thymidine kinase, a luciferase, a β-galactosidase, a chloramphenicol acetyltransferase, a surface receptor, a protein tag, including but not limited to 6×His tag, V5 tag, GFP tag, a self-processing ribozyme cassette, a mevalonate kinase and derivates thereof, a biotin ligase and derivates thereof including but not limited to BirA, a engineered peroxidase and derivates thereof including but not limited to APEX2, an endonuclease or site-specific recombinase and derivates thereof, including but not limited to restriction enzymes, Cre, Flp, Tn5, SpCas9, SaCas9, TALENs, a gene correcting a monogenic disease, a tumour-associated antigen or a gene encoding for an immune modulator to facilitate immunotherapy including but not limited to MAGEA3m GM-CSF, IFNγ, IFNβ, CXCL-9-10-11.
The term “gene” means essentially the coding nucleic acid sequence which is transcribed (DNA) and translated (mRNA) into a polypeptide in vitro or in vivo when operably linked to appropriate regulatory sequences. The gene may or may not include regions preceding and following the coding region, e.g. 5′ untranslated (5′UTR) or “leader” sequences and 3′ UTR or “trailer” sequences, as well as intervening sequences (introns) between individual coding segments (exons).
“Gene expression” as used herein refers to the absolute or relative levels of expression and/or pattern of expression of a gene. The expression of a gene may be measured at the level of DNA, cDNA, RNA, mRNA, proteins or combinations thereof. Gene expression may also be inferred from protein expression.
“Gene expression profile” refers to the levels of expression of multiple different genes measured for a cell type of interest. Gene expression profiles may be measured in a sample, such as samples comprising a variety of cell types, different tissues, different organs, or fluids (e.g., blood, urine, spinal fluid, sweat, saliva or serum) by various methods including but not limited to RNA-SEQ by massively parallel signature sequencing (MPSS), Serial Analysis of Gene Expression (SAGE) technology, microarray technologies, microfluidic technologies, in situ hybridization methods, quantitative and semi-quantitative RT-PCR techniques or mass-spectrometry.
Any methods available in the art for detecting expression of the genes are encompassed herein. By “detecting expression” is intended determining the quantity or presence of an RNA transcript or its expression product e.g. on the protein level.
As used herein, the term “expression level” as applied to a gene refers to the normalized level of a gene product, e.g. the normalized value determined for the RNA expression level of a gene or for the polypeptide expression level of a gene.
The term “gene product” or “expression product” are used herein to refer to the RNA transcription products (transcripts) of the gene, including mRNA, and the polypeptide translation products of such RNA transcripts. A gene product can be, for example, an unspliced RNA, an mRNA, a splice variant mRNA, a microRNA, a fragmented RNA, a polypeptide, a post-translationally modified polypeptide, a splice variant polypeptide, etc. The term “RNA transcript” as used herein refers to the RNA transcription products of a gene, including, for example, mRNA, an unspliced RNA, a splice variant mRNA, a microRNA, and a fragmented RNA.
Methods for detecting expression of the genes of the invention, that is, gene expression profiling, include methods based on hybridization analysis of polynucleotides, methods based on sequencing of polynucleotides, immunohistochemistry methods, and proteomics-based methods. The methods generally detect expression products (e.g., mRNA) of the genes.
Many expression detection methods use isolated RNA. The starting material is typically total RNA isolated from a biological sample, such as the cell type of interest, and a reference cell type, respectively.
General methods for RNA extraction are well known in the art and are disclosed in standard textbooks of molecular biology, including Ausubel et al., ed., Current Protocols in Molecular Biology, John Wiley & Sons, New York 1987-1999. Methods for RNA extraction from paraffin embedded tissues are disclosed, for example, in Rupp and Locker (Lab Invest. 56:A67, 1987) and De Andres et al. (Biotechniques 18:42-44, 1995). In particular, RNA isolation can be performed using a purification kit, a buffer set and protease from commercial manufacturers, such as Qiagen (Valencia, Calif.), according to the manufacturers instructions.
Isolated RNA can be used in hybridization or amplification assays that include, but are not limited to, PCR analyses and probe arrays. One method for the detection of RNA levels involves contacting the isolated RNA with a nucleic acid molecule (probe) that can hybridize to the mRNA encoded by the gene being detected. The nucleic acid probe can be, for example, a full-length cDNA, or a portion thereof, such as an oligonucleotide of at least 7, 15, 30, 60, 100, 250, or 500 nucleotides in length and sufficient to specifically hybridize under stringent conditions to an intrinsic gene of the present invention, or any derivative DNA or RNA. Hybridization of an mRNA with the probe indicates that the intrinsic gene in question is being expressed.
An alternative the level of gene expression in a cell type of interest involves the process of nucleic acid amplification, for example, by RT-PCR (U.S. Pat. No. 4,683,202), ligase chain reaction (Barany, Proc. Natl. Acad. Sci. USA 88:189-93, 1991), self sustained sequence replication (Guatelli et al., Proc. Natl. Acad. Sci. USA 87:1874-78, 1990), transcriptional amplification system (Kwoh et al., Proc. Natl. Acad. Sci. USA 86:1173-77, 1989), Q-Beta Replicase (Lizardi et al., Bio/Technology 6:1197, 1988), rolling circle replication (U.S. Pat. No. 5,854,033), or any other nucleic acid amplification method, followed by the detection of the amplified molecules using techniques well known to those of skill in the art. These detection schemes are especially useful for the detection of nucleic acid molecules if such molecules are present in very low numbers.
In particular, gene expression may be assessed by quantitative RT-PCR. Numerous different PCR or QPCR protocols are known in the art. Generally, in PCR, a target polynucleotide sequence is amplified by reaction with at least one oligonucleotide primer or pair of oligonucleotide primers. The primer(s) hybridize to a complementary region of the target nucleic acid and a DNA polymerase extends the primer(s) to amplify the target sequence. Under conditions sufficient to provide polymerase-based nucleic acid amplification products, a nucleic acid fragment of one size dominates the reaction products (the target polynucleotide sequence which is the amplification product). The amplification cycle is repeated to increase the concentration of the single target polynucleotide sequence. The reaction can be performed in any thermocycler commonly used for PCR. However, preferred are cyclers with real-time fluorescence measurement capabilities.
Quantitative PCR (QPCR) (also referred as real-time PCR) is preferred under some circumstances because it provides not only a quantitative measurement, but also reduced time and contamination. As used herein, “quantitative PCR (or “real time QPCR”) refers to the direct monitoring of the progress of PCR amplification as it is occurring without the need for repeated sampling of the reaction products. In quantitative PCR, the reaction products may be monitored via a signaling mechanism (e.g., fluorescence) as they are generated and are tracked after the signal rises above a background level but before the reaction reaches a plateau. The number of cycles required to achieve a detectable or “threshold” level of fluorescence varies directly with the concentration of amplifiable targets at the beginning of the PCR process, enabling a measure of signal intensity to provide a measure of the amount of target nucleic acid in a sample in real time.
Furthermore microarrays may be used for gene expression profiling. By “microarray” is intended an ordered arrangement of hybridizable array elements, such as, for example, polynucleotide probes, on a substrate. The term “probe” refers to any molecule that is capable of selectively binding to a specifically intended target biomolecule, for example, a nucleotide transcript or a protein encoded by or corresponding to an intrinsic gene. Probes can be synthesized by one of skill in the art, or derived from appropriate biological preparations. Probes may be specifically designed to be labeled. Examples of molecules that can be utilized as probes include, but are not limited to, RNA, DNA, proteins, antibodies, and organic molecules.
DNA microarrays provide one method for the simultaneous measurement of the expression levels of large numbers of genes. Each array consists of a reproducible pattern of capture probes attached to a solid support. Labeled RNA or DNA is hybridized to complementary probes on the array and then detected by laser scanning. Hybridization intensities for each probe on the array are determined and converted to a quantitative value representing relative gene expression levels. See, for example, U.S. Pat. Nos. 6,040,138, 5,800,992 and 6,020,135, 6,033,860, and 6,344,316. High-density oligonucleotide arrays are particularly useful for determining the gene expression profile for a large number of RNAs in a sample.
Serial analysis of gene expression (SAGE) is a method that allows the simultaneous and quantitative analysis of a large number of gene transcripts, without the need of providing an individual hybridization probe for each transcript. First, a short sequence tag (about 10-14 bp) is generated that contains Sufficient information to uniquely identify transcript, provided that the tag is obtained from a unique position within each transcript. Then, many transcripts are linked together to form long serial molecules, that can besequenced, revealing the identity of the multiple tags simultaneously. The expression pattern of any population of transcripts can be quantitatively evaluated by determining the abundance of individual tags, and identifying the gene corresponding to each tag. For more details see, e.g. Velculescu et al., Science 270:484-487 (1995); and Velculescu et al., Cell 88:243-51 (1997).
Nucleic acid sequencing technologies are suitable methods for analysis of gene expression. The principle underlying these methods is that the number of times a cDNA sequence is detected in a sample is directly related to the relative expression of the mRNA corresponding to that sequence.
These methods are sometimes referred to by the term Digital Gene Expression (DGE) to reflect the discrete numeric property of the resulting data. Early methods applying this principle were Serial Analysis of Gene Expression (SAGE) and Massively Parallel Signature Sequencing (MPSS). See, e.g., S. Brenner, et al., Nature Biotechnology 18(6):630-634 (2000).
The advent of “next generation” sequencing technologies has made DGE simpler, higher throughput, and more affordable. As a result, more laboratories are able to utilize DGE to screen the expression of more genes in more cell types of interest than previ ously possible. See, e.g., J. Marioni, Genome Research 18(9): 1509-1517 (2008); R. Morin, Genome Research 18(4):610 621 (2008); A. Mortazavi, Nature Methods 5(7):621-628 (2008): N. Cloonan, Nature Methods 5(7):613-619 (2008).
Next generation sequencing typically allows much higher throughput than the traditional Sanger approach. See Schuster, Next-generation sequencing transforms today's biology, Nature Methods 5:16-18 (2008); Metzker, Sequencing technologies the next generation. Nat Rev Genet. 2010 January; 11(1):31-46. These platforms can allow sequencing of clonally expanded or non-amplified single molecules of nucleic acid fragments. Certain platforms involve, for example, sequencing by ligation of dyemodified probes (including cyclic ligation and cleavage), pyrosequencing, and single-molecule sequencing. Nucleotide sequence species, amplification nucleic acid species and detectable products generated there from can be analyzed by such sequence analysis platforms. Next-generation sequencing can be used in the methods of the invention, e.g. to determine the gene expression profile or the genomic sequence data of the cell type of interest.
RNA Sequencing (RNA-Seq) uses massively parallel sequencing to allow for example transcriptome analyses of genomes at typically a far higher resolution than is available with Sanger sequencing- and microarray-based methods. In the RNA-Seq method, complementary DNAs (cDNAs) generated from the RNA of interest are directly sequenced using next-generation sequencing technologies. RNA-Seq has been used successfully to precisely quantify transcript levels, confirm or revise previously annotated 5′ and 3′ ends of genes, and map exon/intron boundaries (Eminaga et al., 201 3. Quantification of microRNA Expression with Next-Generation Sequencing. Current Protocols in Molecular Biology. 103:4.1 7.1-4.1 7.14).
As used herein, “sequencing” thus refers to any technique known in the art that allows the identification of consecutive nucleotides of at least part of a nucleic acid. Exemplary sequencing techniques include Illumina™ sequencing, direct sequencing, random shotgun sequencing, Sanger dideoxy termination sequencing, whole-genome sequencing, massively parallel signature sequencing (MPSS), RNA-seq (also known as whole transcriptome sequencing), sequencing by hybridization, pyrosequencing, capillary electrophoresis, gel electrophoresis, duplex sequencing, cycle sequencing, single-base extension sequencing, solid-phase sequencing, high-throughput sequencing, massively parallel signature sequencing, emulsion PCR, sequencing by reversible dye terminator, paired-end sequencing, near-term sequencing, exonuclease sequencing, sequencing by ligation, short-read sequencing, single-molecule sequencing, sequencing-by-synthesis, real-time sequencing, reverse-terminator sequencing, nanopore sequencing, 454 sequencing, Solexa Genome Analyzer sequencing, SOLiD™ sequencing, Illumina Hiseq4000, Illumina NextSeq500, Illumina MiSeq and Miniseq, MS-PET sequencing, mass spectrometry, and a combination thereof.
Gene expression profiles may also be deduced from information on the proteome. The term “proteome” is defined herein as the totality of the proteins present in a cell type at a certain point of time. Proteomics includes, among other things, study of the global changes of protein expression in a sample (also referred to as “expression proteomics”). Proteomics typically includes the following steps: (1) separation of individual proteins in a sample by 2-D gel electrophoresis (2-D PAGE); (2) identification of the individual proteins recovered from the gel, e.g. my mass spectrometry or N-terminal sequencing, and (3) analysis of the data using bioinformatics.
The term “genome,” as used herein, generally refers to the complete set of genetic information in the form of one or more nucleic acid sequences, including text or in silico representations thereof. A genome may include either DNA or RNA, depending upon its organism of origin. Most organisms have DNA genomes while some viruses have RNA genomes. As used herein, the term “genome” need not comprise the complete set of genetic information. The term may also refer to at least a majority portion of a genome such as at least 50% to 100% of an entire genome or any whole or fractional percentage therebetween.
The term “genomic sequence data” refers to data, including text or in silico representations thereof, on a genome, wherein the genomic sequence data may also relate to a genome preferably the majority of the genome, such as at least 50% to 100% of an entire genome or any whole or fractional percentage therebetween.
The provision of genomic sequence data of may include the actual sequencing of the genome of a cell type of interest or the reliance upon publically available data bases on genome sequence data such as the annotated Genome Sequence DataBase (GSDB), operated by the National Center for Genome Resources (NCGR). The provision of genomic sequence data for a large number of species is publicly available through The UCSC Genome Browser created by the UCSC Genome Browser Group of UC Santa Cruz (CA, USA).
The term “genomic region” as used herein, generally refers to a region a genome. Typically a genomic region refers to a continuous nucleic acid sequence stretch of the genome of the cell type of interest comprising at least one gene.
The term “genomic sub-region” refers to a portion of the a genomic region that is identified as described herein to comprise one or more binding sites for one or more of the transcription factors that have been identified as signature genes based upon the gene expression profile(s).
The term “nucleic acid” refers to any nucleic acid molecule, including, without limitation, DNA, RNA and hybrids or modified variants and polymers (“polynucleotides”) thereof in either single- or double-stranded form. Unless specifically limited, the term encompasses nucleic acids containing known analogues of natural nucleotides that have similar binding properties as the reference nucleic acid and are metabolized in a manner similar to naturally occurring nucleotides. Unless otherwise indicated, a particular nucleic acid molecule/polynucleotide also implicitly encompasses conservatively modified variants thereof (e.g. degenerate codon substitutions) and complementary sequences as well as the sequence explicitly indicated. Specifically, degenerate codon substitutions may be achieved by generating sequences in which the third position of one or more selected (or all) codons is substituted with mixed-base and/or deoxyinosine residues (Batzer et al., Nucleic Acid Res. 19: 5081 (1991); Ohtsuka et al., J. Biol. Chem. 260: 2605-2608 (1985); Rossolini et al., Mol. Cell. Probes 8: 91-98 (1994)). Nucleotides are indicated by their bases by the following standard abbreviations: adenine (A), cytosine (C), thymine (T), and guanine (G).
An “exogenous nucleic acid” or “exogenous genetic element” relates to any nucleic acid introduced into the cell, which is not a component of the cells “original” or “natural” genome. Exogenous nucleic acids may be integrated or non-integrated, or relate to stably transfected nucleic acids.
“Functional variants” or “functional analogs” preferably refers to a nucleic acid or protein having a nucleotide sequence or amino acid sequence, respectively, that is “identical,” “essentially identical,” “substantially identical,” “homologous” or “similar” to a reference sequence which can, by way of non-limiting example, be the sequence of an isolated nucleic acid or protein, or a consensus sequence derived by comparison of two or more related nucleic acids or proteins, or a group of isoforms of a given nucleic acid or protein. Non-limiting examples of types of isoforms include isoforms of differing molecular weight that result from, e.g., alternate RNA splicing or proteolytic cleavage; and isoforms having different post-translational modifications, such as glycosylation; and the likes.
As used herein, the term “variants” or “analogs” refers to a nucleic acid or polypeptide differing from a reference nucleic acid or polypeptide, but retaining essential properties thereof. Generally, variants are overall closely similar, and, in many regions, identical to the reference nucleic acid or polypeptide. Thus “variant” forms of a transcription factor are overall closely similar, and capable of binding DNA and activate gene transcription.
As used herein, the term “sense strand” refers to the DNA strand of a gene that is translated or translatable into protein. When a gene is oriented in the “sense direction” with respect to the promoter in a nucleic acid sequence, the “sense strand” is located at the 5′ end downstream of the promoter, with the first codon of the protein is proximal to the promoter and the last codon is distal from the promoter. The opposite is referred to as the “anti-sense” strand.
As used herein, the term “operably linked” refers to that the regulatory elements in the nucleic acid construct are configured to enable functional coupling between the regulatory element and gene, leading to expression of the gene, ie the regulatory element is preferably in-frame with a nucleic acid coding for a protein or peptide.
As used herein the term “comprising” or “comprises” is used in reference to expression cassettes, reporter vectors, and respective component(s) thereof, that are open to the inclusion of unspecified elements.
The term “consisting of” refers to expression cassettes, reporter vectors, and respective component(s) thereof as described herein, which are exclusive of any element not recited in that description of the embodiment.
The term “signature genes” relates to genes that are selected from the genes of the cell type of interest genes that are characteristic for the expression profiles of said cell type of interest. Differentially regulated signature genes may be e.g. selected by identifying genes that are up- or down-regulated compared to the expression levels in the reference cell type, or by ranking the gene expression level for the cell type of interest and selecting signature genes based upon a threshold level or predetermined number of genes (e.g. most highly or most lowly expressed).
As used herein the term “transcription factor” refers to a protein that binds to specific DNA sequences and thereby controls the transfer (or transcription) of genetic information from DNA to mRNA. The function of transcription factors is primarily to regulate the expression of genes. Transcription factors may function alone or in combination with further proteins in a complex, by promoting (as an activator), or blocking (as a repressor) the recruitment of RNA polymerase to specific genes. Transcription factors contain at least DNA-binding domain, which attaches to a specific sequence of DNA (“binding sites”) typically adjacent to the genes that they regulate.
The term “microscopic device” relates to a device that comprises means for microscopic analysis of cells. Microscopic analysis can be carried out, without limitation, by a light microscope, binocular stereoscopic microscope, bright field microscope, polarizing microscope, phase contrast microscope, differential interference contrast microscope, automatic microscope, fluorescence microscope, confocal microscope, total internal reflection fluorescence microscope, laser microscope (laser scanning confocal microscope), multiphoton excitation microscope, structured illumination microscope, transmission electron microscope (TEM), scanning electron microscope (SEM), atomic force microscope (AFM), scanning near-field optical microscope (SNOM), X-ray microscope, ultrasonic microscope. Microscopic devices can additionally comprise a camera and/or detector for recording pictures of cells, for example, and a computer system for controlling the microscopic device.
The presence and/or intensity of a signal produced by reporter gene can be determined by means of a microscopic device, but also by other devices that can detect signals generated by reporter genes without limitation, such as flow cytometers, luminometers, spectrometers, photometers, or colorimeters.
As used herein the term “topological associating domains” preferably refers to a self-interacting genomic region, meaning that DNA sequences within a topological associating domain physically interact with each other more frequently than with sequences outside the topological associating domain, thereby forming a three-dimensional chromosome structures. Topological associating domains can range in size from thousands to millions of DNA bases. A number of proteins are known to be associated with topological associating domains formation including the protein CTCF and the protein complex cohesin. In preferred embodiments the topological associating domains refers to a genomic sequence between two CTFC or cohesin binding sites.
As used herein, the term “generating a cell-type specific expression cassette” relates in some embodiments to the design of a cell-type specific expression cassette without physically producing the corresponding nucleic acid molecule, for example the method may be a computer-implemented method or may comprise one or more computer-implemented steps in the method.
As used herein, the term “generating a cell-type specific expression cassette” relates in some embodiments to the design and physical production of a nucleic acid molecule, preferably by de novo synthesis of the nucleic acid molecule.
Artificial gene synthesis (or de novo synthesis) is a preferred method of generating a cassette of the present invention and relates to methods used in synthetic biology to create any given nucleic acid sequence. In some cases based on solid-phase DNA synthesis, artificial synthesis differs from molecular cloning and polymerase chain reaction (PCR) in that the user does not have to begin with pre-existing DNA sequences. Therefore, it is possible to make a completely synthetic double-stranded DNA molecule with no major limits on either nucleotide sequence or size. Gene synthesis approaches may be based on a combination of organic chemistry and molecular biological techniques and entire genes may be synthesized “de novo”, without the need for precursor template DNA. The method has been used to generate functional bacterial chromosomes containing approximately one million base pairs. Gene synthesis has become an important tool in many fields of recombinant DNA technology including heterologous gene expression, vaccine development, gene therapy, vector construction and various forms of molecular engineering. The synthesis of nucleic acid sequences is often more economical than classical cloning and mutagenesis procedures. Multiple techniques are well-established and known to a skilled person.
The term “gene therapy” preferably refers to the transfer of DNA into a subject in order to treat a disease. The person skilled in the art knows strategies to perform gene therapy using gene therapy vectors. Such gene therapy vectors are optimized to deliver foreign DNA into the host cells of the subject. In a preferred embodiment the gene therapy vectors may be a viral vector. Viruses have naturally developed strategies to incorporate DNA in to the genome of host cells and may therefore be advantageously used. Preferred viral gene therapy vectors may include but are not limited to retroviral vectors such as moloney murine leukemia virus (MMLV), adenoviral vectors, lentiviral, adenovirus-associated viral (AAV) vectors, pox virus vectors, herpes simplex virus vectors or human immunodeficiency virus vectors (HIV-1). However also non-viral vectors may be preferably used for the gene therapy such as plasmid DNA expression vectors driven by eukaryotic promoters or plasmid DNA sequence containing homology to the host genome in order to directly integrate the expression cassette at preferred locations in the genome of interest. DNA transfer may also be carried out using liposomes or similar extra-cellular vescicles. Furthermore preferred gene therapy vectors may also refer to methods to transfer of the DNA such as electroporation or direct injection of nucleic acids into the subject. The person skilled in the art knows how to choose preferred gene therapy vectors according the need of application as well as the methods on how to implement nucleic acid constructs such as the expression cassettes described herein into the gene therapy vector. (P. Seth et al., 2005, N. Koostra et, al. 2009., W. Walther et al. 2000, Waehler et al. 2007).
The method, system, or other computer implemented aspects of the invention may in some embodiments comprise and/or employ one or more conventional computing devices having a processor, an input device such as a keyboard or mouse, memory such as a hard drive and volatile or nonvolatile memory, and computer code (software) for the functioning of the invention.
The system may comprise one or more conventional computing devices that are pre-loaded with the required computer code or software, or it may comprise custom-designed software and/or hardware. The system may comprise multiple computing devices which perform the steps of the invention. In certain embodiments, a plurality of clients such as desktop, laptop, or tablet computers can be connected to a server such that, for example, multiple users can provide data or perform calculations at different steps of the method. The computer system may also be networked with other computers or necessary databases, such as genomic databases, over a local area network (LAN) connection or via an Internet connection. The system may also comprise a backup system which retains a copy of the data obtained by the invention. The data connections necessary between the various steps of the method may be conducted or configured via any suitable means for data transmission, such as over a local area network (LAN) connection or via an Internet connection, either wired or wireless.
A client or user computer can have its own processor, input means such as a keyboard, mouse, or touchscreen, and memory, or it may be a terminal which does not have its own independent processing capabilities, but relies on the computational resources of another computer, such as a server, to which it is connected or networked. Depending on the particular implementation of the invention, a client system can contain the necessary computer code to assume control of the system if such a need arises. In one embodiment, the client system is a tablet or laptop.
The components of the computer system for carrying out the method may be conventional, although the system may be custom-configured for each particular implementation. The computer implemented method steps or system may run on any particular architecture, for example, personal/microcomputer, minicomputer, or mainframe systems. Exemplary operating systems include Apple Mac OS X and iOS, Microsoft Windows, and UNIX/Linux; SPARC, POWER and Itanium-based systems; and z/Architecture. The computer code to perform the invention may be written in any programming language or model-based development environment, such as but not limited to C/C++, C#, Objective-C, Java, Basic/VisualBasic, MATLAB, R, Simulink, StateFlow, Lab View, or assembler. The computer code may comprise subroutines which are written in a proprietary computer language which is specific to the manufacturer of a circuit board, controller, or other computer hardware component used in conjunction with the invention.
The information processed and/or produced by the method, ie as digital representations of nucleic acid sequences, gene expression profiles, lists of genes and/or particular sequence elements such as TF binding sites, can employ any kind of file format which is used in the industry. For example, the digital representations can be stored in a proprietary format, DXF format, XML format, or other format for use by the invention. Any suitable computer readable medium may be utilized. The computer-usable or computer-readable medium may be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a transmission media such as those supporting the Internet or an intranet, cloud storage or a magnetic storage device.
In Table 1 the nucleotide sequence of preferred embodiments of minimal sets of genomic subregions for a cell-type specific reporter vector (i.e. synthetic locus regions) are listed
In one embodiment the invention therefore encompasses a vector comprising a nucleic acid molecule selected from the group consisting of:
Functionally analogous sequences refer preferably to the ability of the synthetic regulatory regions to promote transcription of an operably coupled reporter or effector gene in a cell type of interest.
In one embodiment the invention encompasses a vector for oncolytic viral therapy comprising a nucleic acid molecule selected from the group consisting of:
Functionally analogous sequences refer preferably to the ability of the synthetic regulatory regions to promote transcription of viral essential genes and/or effector genes such as co-stimulatory molecules (e.g. cytokines/chemokines) in the diseases target cell of interest and not in non-diseased cells.
The invention is further described by the following figures. These are not intended to limit the scope of the invention but represent preferred embodiments of aspects of the invention provided for greater illustration of the invention described herein.
The invention is further described by the following examples. These are not intended to limit the scope of the invention but represent preferred embodiments provided for greater illustration of the invention described herein. The examples show that the methods and reporter vectors described herein allow for cell-type specific expression of reporter and effectors genes in various cell types of interest.
Materials and Methods Used in the Examples:
sLCRs generation and TFBS discovery: High-affinity, TF-binding sites in defined genomic regions (DRG loci; table X) were identified using FIMO (PMID: 21330290) with -output-pthresh 1e-4-no-qvalue. A database of 1,818 models representing known transcription factor binding preferences (position weight matrices, PWM) was generated from the literature (Portales-Casamar et al., 2010; Badis et al., 2009; Berger et al., 2008; Bucher, 1990; Jolma et al., 2010). PWMs were pre-selected based on subtype-specific TFs. Regions corresponding to DRGs were retrieved from the UCSC genome browser (hg19; Refseq table downloaded on Oct. 5, 2012) and scanned with windows of 150 bp and 50 bp steps (hereafter refer as cis-units). The scanned area surrounding each signature gene was delimited by two distal CTCF sites, positioned >10 kb away from the TSS or TES. Subtype-specific PWMs were mapped to the genomic regions using FIMO. PWMs best significantly over-represented regions (adj. p.value <0.01; multiple backgrounds). For each window, whenever multiple matches for the same PWM were identified, the p-value of the best match was considered as a proxy for the affinity of that TF over that region. Given a region, an overall score was calculated based on the sum of the best−log 10(p-value) for each PWM considered. Significantly over-represented regions (multiple backgrounds) were determined by comparing motifs/background (empirical p-value <0.01). TFBS pairwise correlation heatmaps in
Automation of sLCRs generation: To focus on cell intrinsic gene signatures, in a pilot approach, we filtered out genes lowly expressed in GBM stem-like cells (GSCs) from our previous experiments whereas current implementations of the method involve focusing on a validated Glioma-intrinsic signature20. The first sLCRs were designed with manual selection of the top scoring cis-units based on PWM score and diversity. Also, the selection of the TSS-containing region was done manually. The automated sLCR generation is written in python (URL GitHub/GitLab). The script takes as input a list of TFs, PWM, and the phenotype gene signature. With these, it generates cis-units from the defined cis-regulatory regions (default parameters: 150 bp windows/50 bp steps). The selection of the best cis-units for any given a phenotype is generated by using an algorithm based on defined selection rules. The algorithm first generates the ranking and the selection of the best cis-unit by applying the following formula: [Sum of scores−log 10(pvalue)*diversity (number of different TFBS)]. Iteratively, it removes the TFBS included in the selected cis-units. In order to increase the chances of successful transcriptional firing, the algorithm ranks cis-units also based on 5′ CAGE data. The ranked list is the output of the algorithm. The automated procedure returned overlapping results with the manual selection (
RNA-seq generation: RNA was extracted using Trizol (Invitrogen), precipitated using Isopropanol and purified using RNAClean XP beads. RNA-seq libraries generated for this study were constructed using the TruSeq Stranded Total RNA library prep kit. Beads-based approach was used for rRNA depletion (Ribo-Zero Gold; Illumina) and PCR amplification was performed as per the manufacturer's protocol. Final libraries were analyzed on Bioanalyzer or TapeStation and barcoded libraries were pooled and sequenced on an Illumina HiSeq2500 or HiSeq4000 platforms with either single-read 51 bp or paired-end 100-base protocols. Illumina adaptors were trimmed using from the raw reads with Cutadapt, and raw reads were aligned to the human genome (Hg19 or Hg38) with TopHat. HTSeq was used to assess the number of uniquely assigned reads for each gene; expression values were then normalized to 107 total reads and log 2 transformed to obtain counts per millions (CPM).
Analysis: For the heatmap in
In
ATAC-seq: ATAC-seq on FACS sorted populations was performed on 20-50,000 cells from the in vivo experiment, and 50-100,000 from the in vitro experiment. Cells were centrifuged in PBS and gently resuspend the pellet in 50 μl of master mix (25 μL 2×TD buffer, 2.5 μL transposase and 22.5 μL nuclease-free water, Nextera DNA Library Prep, Illumina), incubated 60 min, 37° C. with moderate shaking (500-800 rpm). Transposition was stopped by 5 μl of Proteinase K and 50 ul of AL buffer (Quiagen), incubated at 56 C for 10 min and DNA purified using 1.8× vol/vol AMPure XP beads and eluted in 18 ul. The optimal number of PCR cycles for library amplification was determined per each sample using 2 ul of template followed by qPCR amplification using heat activated Kappa Hifi polymerase and EvaGreen 1×. Final amplification was performed in 50 ul qPCR volume and 8-12 ul of template DNA. Primers were previously described (Buenrostro et al. 201). Libraries were individually quantified using Qubit (Life Technologies) and appropriate ladder distribution was determined on TapeStation (Agilent) using the High Sensitivity D1000 ScreenTapes. Sequencing was performed on an Illumina NextSeq 500 using V2 chemistry for 150 cycles (paired-end 75nt). ATAC-seq scatter analysis in
ATAC-seq analysis Reads were adapter removed using trim-galore v0.6.2-nextera, then mapped using bowtie2 v2.3.5 (reference) default parameters. ATAC-seq analysis was performed using SeqMonk, by using as probes TSS±5 kb final annotation on ENSEMBL mRNAs (2019 assembly). Counts were normalized using Read Count Quantitation function, and reads were corrected for total count only in probes per million reads, log transformed and further transformed by size factor normalization. Integration of sLCR ATAC-seq and TCGA ATAC-seq of
Vector generation: The sLCRs were synthetized initially at IDT and later at GenScript. MGT #1-mVenus was cloned in the Pacl-BsrGl fragment of the Mammalian Expression, Lentiviral FUGW (gift from David Baltimore; Addgene #14883). Additional modifications, such as swapping of mVenus to mCherry, or MGT #1 with all other sLCR used either restriction enzyme digestion or Gibson cloning. The sLCRs vectors are 3rd gen lentiviral system and have been used together with pCMV-G (Addgene #8454), pRSV-REV (Addgene #12253) and pMDLG/pRRE (Addgene #12251). Sall2 (ccsbBroad304_11117) Pou3f2 (ccsbBroad304_14774) were obtained from the CCSB-Broad Lentiviral Expression Library.
Cell lines: The MES-hGICs and PN-hGICs were generated by our lab and will be described elsewhere. Briefly, a PN-hGICs were generated by transforming human NPC, by means of: pLenti6.2/V5-IDH1-R132H, TP53R173H and TP53R273H (point mutations introduced into TP53 ccsbBroad304_07088 from the CCSB-Broad Lentiviral Expression Library, and pRS-Puro-sh-PTEN(#1). MES-hGICs were generated by transforming human NPC pRSPURO-sh-PTEN(#1), pLKO.1-sh-TP53 (TRCN0000003754) and pRS-shNF1. For these lines, thorough genetic, transcriptional and epigenetic characterization has been performed, as well as in vivo tumor formation and phenotypic mimicking ability. In vitro, GICs were propagated as described76 with one modification. In addition to with EGF (20 ng/ml; R&D), bFGF (20 ng/ml; R&D), heparin (1 μg/ml; Sigma) and 5% penicillin and streptomycin, PDGF-AA (20 ng/ml; R&D) is also supplemented to RHB-A (Takara). This medium composition will be referred to as RHB-A complete. hGICs were cultured at 37° C. in a 5% CO2, 3% O2 and 95% humidity incubator.
The T98G and U87MG (kindly provided by the van Tellingen lab, NKI) were propagated in EMEM medium. For the experiments in
The MCF7, MDA-231, A549 and H1944, cell lines (kindly provided by the Rene Bernards lab, NKI) were cultured in RPMI medium. All cell lines were supplemented with 10% FBS, and 5% penicillin and streptomycin at 37° C. in a 5% CO2-95% air incubator.
Immortalized primary human Microglia C20 were cultured in RHB-A medium (Takara) supplemented with 1% FBS, 2.5 mM Glutamine (Thermofisher; 35050038), 1 μM Dexamethasone (Sigma; D1756) and 1% penicillin and streptomycin at 37° C. in a 5% CO2, 19% O2 and 95% humidity incubator.
Donor-derived CD34 cells were propagated in SFEM II (StemCell), SCF, FLT3-L, TPO, IL6 (all 100 ng/ml; easyexperiments.com), UM171 (Selleck, 0.035 μM), SR1 (Selleck, 0.75 μM), 19-deoxy-9-methylene-16,16-dimethyl PGE2 (Cayman, 10 μM).
Genome-wide CRISPR Knock-out in vitro screen: For the genome-wide pooled CRISPR Knock-out screen, we utilized the Brunello library consisting of 77,441 sgRNAs targeting 19,114 genes (average of 4 sgRNAs per gene) and 1000 non-targeting controls. To achieve a library representation over 100×, we transduced a total of 16×106 MES-hGICs-MGT #1low cells at a MOI of ˜0.5 and amplified the cells for 10 days prior introducing the treatment. At day 10, the cells were either treated with TNFa (10 ng/ml) and FBS (0.5%); Temozolomide (50 μM) and Irradiation (20 Gy) or left untreated. Before the gDNA extraction, we performed a FACs sorting of each condition, collecting the MES-hGICs-MGT #1low, MES-hGICs-MGT #1high and the unsorted populations. The genomic DNA was extracted by lysing the cell pellets for 10′ at 56° C. in AL buffer (Qiagen), supplemented with Proteinase K (Invitrogen) and RNAse A (Thermo Scientific), subsequently purified with AMPure beads and eluted in EB buffer (Qiagen). NGS libraries were constructed in a two-step PCR setup, where the PCR1 is used to amplify the sgRNA scaffold and insert a stagger sequence to increase library complexity across the flow cell, while the PCR2 introduced Illumina compatible adaptors with unique P7 barcodes, allowing sample multiplexity. For the PCR1, 5 μg of each gDNA sample were divided over 5 parallel reactions, that were subsequently pooled together and purified using AMPure beads. The optimal cycle numbers for PCR2 were determined for 1 μl of each PCR1 individually by conducting a qPCR amplification using KAPA HiFi HotStart Ready Mix (Roche) and 1× EvaGreen (Biotium). 10 μl of the purified PCR1 of each sample were used as input for the final PCR2. Both PCR1 and PCR2 were performed using KAPA HiFi HotStart Ready Mix. Primers are available upon request. Quality control of the final libraries was performed using the Qubit dsDNA HS kit (Invitrogen) for quantification and TapeStation High Sensitivity D1000 ScreenTapes (Agilent) for determination of PCR fragment size. The barcoded libraries were pooled together in equal molarities and sequenced on an Illumina NextSeq500 using the 75 cycles V2 chemistry (1×75 nt single read mode).
Transwell co-culture: Co-cultures of hGICs and immortalized primary human Microglia C20 were set up using hydrophilic PTFE 6-well cell culture inserts with a pore size of 0.4 μm (Merck). Human Microglia were seeded at 1.5×105 cells/well for 24 h on 6-well plates in respective medium. Medium was aspirated and cells were washed once with PBS before 1 ml of RHB-A complete medium was added. Transwell inserts were placed into plates and 5×105 single hGICs in a total volume of 1 ml of RHB-A complete medium were plated on insert surface. hGICs and C20 human Microglia were harvested after 48 h of co-culture for further analysis.
Transfection-Transduction: Transfection and transduction were previously described in detail. Briefly, 12 μg of DNA mix (lentivector, pCMV-G, pRSV-REV, pMDLG/pRRE were incubated with the FuGENE-DMEM/F12 mix for 15 min at RT, added to the antibiotic-free medium covering the 293T cells and the a first-tap of viral supernatant was collected at 40 h after transfection. Titer was assessed using Lenti-X p24 Rapid Titer Kit (Takara) according to the manufacturer's instructions. We applied viral particles to target cells in the appropriate complete medium supplemented with 2.5 μg/ml protamine sulfate. After 12-14 h of incubation with the viral supernatant, the medium was refreshed with the appropriate complete medium.
Preparation of cryosections: Tumorspheres were allowed to settle by gravity, fixed in fresh prepared formaldehyde in PBS (1.0%), which was blocked with 140 mM glycine 2M, rinsed with 30% sucrose, followed by addition of freezing medium (O. C. T/cryomold). Frozen block were obtained by dry ice freezing and stored at −80° C. until used. The blocks were cut with Leica CM 1950.
Immunohistochemistry: Tissues or tumorspheres were fixed in 4% PFA for 20′. Following fixation, dehydration was performed with increasing EtOH from 70% to 100%, Xylene and overnight Paraffin incubation. Paraffin-embedded samples (PES) were cut using a HM 355S microtome (Thermo Scientific). Hematoxylin/Eosin (HE) staining was performed with standard and slides images were acquired with an automated microscope (Keyence).
Immunofluorescence: At RT, cells were grown on coverslip or spheroids spinned down on glass followed by 4% paraformaldehyde, (PFA, 16005—Sigma Aldrich) in PBS for 10 min fixation, washed in PBS 5 min (3×), permeabilized with 0.5% triton X100 in PBS for 5 min, blocked 15 min with 4% BSA (3854.4 ROTH), stained with primary and secondary antibodies and 20 μm/ml Hoechst 33258 (16756-50, Cayman), and mounted onto glass slides using nail polish and Vectashield (H1000-Linaris). On paraffin-embedded tissues, we performed Deparaffinization and Citrate antigen retrieval with standard protocols. Permeabilization was performed with Triton 0,25% in PBS and—when appropriate—endogenous peroxidases were blocked with 3% H2O2 in water. Typically, we performed blocking with 5% normal goat serum (NGS). Primary antibodies were: anti-GFP (Anti-GFP ab6556, 1:000), anti-MED1 (Abcam ab64965 1:500), anti-Tubulin (BD T5168, 1:2000), and secondary antibodies were: A31573, A11055 and A31571 Alexa Fluor 647, A21206 Alexa Fluor 488, A31570 Alexa Fluor 555.
RNA FISH and dual FISH-IF: Cells were permeabilized in 70% ethanol (RNA FISH only) or with 0.5% triton X-100 (for dual IF-RNA FISH), washed in RNase-free PBS (1×(Life Technologies, AM9932), fixed with 10% Deionized Formamide (EMD Millipore, S4117) in 20% Stellaris RNA FISH Wash Buffer A (Biosearch Technologies, Inc., SMF-WA1-60) and RNase-free PBS, for 5 min at RT. IgK-MGT #1-mVenus and H2B-CFP were probed using SMF-1084-5 CAL Fluor® Red 635 and SMF-1063-5 Quasar® 570 custom Stellaris® FISH Probes (oligo sequence available upon request) in 10% Deionized Formamide 90% Stellaris RNA FISH Hybridization Buffer (Biosearch Technologies, SMF-HB1-10) at 31.5 μM in 100 μL transferred to the coverglass, hybridized at 37° C. in the dark. After 0/N incubation, slides were washed with RNase-free PBS 5 min (3×). If primary/secondary staining occurred, it was as described above.
Imaging: Microscopes used were Zeiss LSM800, Leica SP5-7-8, Nikon Spinning Disk. Confocal images in Figure S41 were acquired with a Leica SP5. mVenus fluorescence was acquired using Ex=488 nm, Em=535 nm and those in
Phenotypic screening: Tumor cells were propagated as described above until the screening. Then we seeded 15′000/50 μl/well in 384 well plates (Corning), in Gibco FluoroBrite DMEM medium supplemented with the appropriate growth factors. Cells were dispensed as 50 μl suspension into each well using the SPARK20M Injector system (50 μl injection volume; 100 μl/s injection speed). For non-adherent cells (e.g. GICs), cells were further centrifuge at 1500 rpm for 1 h30 min at 37° C. Bottom reading fluorescence was scanned using a SPARM 20M TECAN plate reader at 37° C. in a 5% CO2-95% air (3% for GICs) in a humidified cassette, with the following settings for mVenus: Monochromator, Ex 505 nm±20 nm, Em 535 nm±7.5 nm, manual gain:198, flashes: 35, Integration time:40 μs. In independent replicas, cell viability was measured with 0.02% AlamarBlue solution in FluoroBrite medium with the following settings: Fluorescence Top reading. Monochromator, Ex 565 nm±10 nm, Em 592 nm±10 nm, manual gain: 88, flashes: 30, Integration time:40 μs.
DMSO-soluble compounds such as GSK126, were robotically aliquoted using a D300e, whereas cytokines were robotically aliquoted to each well using an Andrew pipetting robot (AndrewAlliance), using the following concentrations:
Data were imported in PRISM7 (GraphPad). Fluorescence intensity from control dead cells was subtracted as background from all values. Individual values were normalized to the mean of controls and represented as Fold change.
Drug dose-response screening: Transduced hGICs from transwell co-culture experiments were harvested into single cell suspension and sorted into mVenus high and low populations using a BD FACSAria III. Cells were counted and 7000 cells/50 μl/well were seeded onto 384-well black walled plates in RHB-A complete medium using the SPARK20M Injector system (50 μl injection volume; 100 μl/s injection speed). Drugs were typically dissolved as a 10 mM stock in DMSO and dispensed using the D300e compound printer (TECAN) for targeted dose-response with plate randomization and DMSO normalization. After 72 h of incubation, cell viability was measured after 2-6 h incubation with 10 μl of Cell-Titer-Blu (Promega) assay reagent with the following settings: Fluorescence top reading. Monochromator, Ex 565 nm±10 nm, Em 592 nm±10 nm, gain setting: optimal scanning, flashes: 30, Integration time: 40 μs. Data were imported in PRISM7 (GraphPad). Fluorescence intensities from empty wells was subtracted as background from all values. Concentrations were log 10-transformed into log[M] scale and individual values were normalized to the mean of untreated positive and SDS treated negative control conditions. Non-linear regression modelling (log(inhibitor) vs. normalized response—Variable slope) was used to derive dose-response curve and IC50 values.
Irradiation of hGICs: Irradiation was delivered using the XenX irradiator platform (XStrahl Life Sciences), equipped with a 225 kV X-ray tube for targeted irradiation. hGICs cultured in either 6-well plates or 96-well plates were placed in the focal plane of the beamline and exposed to irradiation for a specific time, depending on the target dosage, as calculated with an internal calculation software.
Generation of Matrigel organoids: To generate organoids with co-culture of C20 human Microglia and hGICs, growth-factor reduced and phenol-red free Matrigel (BD; 734-1101) droplets were used as an extracellular matrix support. Target cells were harvested and single cell suspensions with 1.5×105 of C20 human Microglia and 3.5×105 of hGICs in a volume of 500 μl were prepared. Using pre-cooled consumables and pipette tips, 30 μl of Matrigel, thawed on ice, was added to each well of cold 60-well Minitrays (Thermofisher; 439225). 5000 cells per droplet were injected using 5 μl of the prepared cell suspension into each organoid and mixed by pipetting. Droplets were cultured for up to 14 days at 37° C. in a 5% CO2, 3% O2 and 95% humidity incubator and RHB-A complete medium was changed every 2-3 days. Live-cell imaging was performed on day 10 using a Leica SP8 confocal microscope.
RT-qPCR: cDNA was generated using SuperScript™ VILO™MasterMix RNA (0.5-2.5 μg) in 20 μL incubated at 25° C. for 10′, at 42° C. for 60′ and at 85° C. for 5′. RT-qPCR was performed with 10 ng cDNA/well, in a 384w ViiA™ 7 System using 1× PowerUp SYBR Green Master Mix (Applied Biosystems), in 10μ/well. Primers are available upon request.
Tissue dissection and Cell surface staining: Brain tumor dissection was previously described in detail77. Briefly, the tissue was dissected with a scalpel, digested in Accutase/DNasel (947 μl Accutase, 50 μl DNase I Buffer, 3 μl DNase I) at 37° C. until needed. Filtered through a 120 μm cell strainer first and a 40 μm cell strainer before RBC lysis (NH4Cl, 155 mM; KHCO3, 10 mM; EDTA, pH 7.4, 0.1 mM). After washing in cold PBS, viability and cell count were assessed automatically with 0.4% Trypan Blue staining using a TECAN SPARK20M.
When surface markers were assessed, typically, 200.000 cells/antibody were used in 15 ml Falcons. Staining volume was 50 μl in RHB-A medium with primary antibody (e.g. CD133-APC; Miltenyi), on ice, in the dark, for 30′. Unbound antibody was removed with two washes of PBS. Depending on whether cells were analyzed or sorted, data acquisition was performed on the BD LSRFortessa or cells were sorted using the BD Aria II or a Astrios Moflo. The appropriate laser-filter combinations were chosen depending on the fluorophores being analyzed. Typically, to remove dead cells, events were first gated on the basis of shape and granularity (FSC-SSC), and we used as viability dyes either AnnexinV or LIVE/DEAD Fixable Aqua Dead Cell Stain Kit (depending on the fluorophores being analyzed). Analysis was performed with FlowJo_V10.
FACS analysis: Analysis was performed with FlowJo_V10.
FACS sorting: Transduced hGICs were harvested into single cell suspensions and resuspended into cold RHB-A complete and filtered into FACS tubes. Sorting was conducted using BD FACSAria III or Fusion. The appropriate laser-filter combinations were chosen depending on the fluorophores being sorted for. Typically, to remove dead cells, events were first gated on the basis of shape and granularity (FSC-A vs. SSC-A) and doublets were excluded (FSC-A vs. FSC-H). Positive gates were established on PGK-driven and constitutively expressed H2B-CFP as sorting reporter, to sort for populations with low to medium intensity of sLCR-dependent fluorophore expression.
Immunoblot: Cell pellets were lysed in RIPA buffer (20 mM Tris-HCl pH7.5, 150 mM NaCl, 1 mM EDTA, 1 mM EGTA, 1% NP-40) supplemented with a 1× Protease inhibitor cocktail (Roche), 10 mM NaPPi, 10 mM NaF, and 1 mM Sodium orthovanadate. The lysates were sonicated if necessary, and electrophoresis was performed using NuPAGE Bis-Tris precast gels (Life Technologies) in NuPAGE MOPS SDS Running Buffer (50 mM MOPS, 50 mM Tris Base, 0.1% SDS, 1 mM EDTA). Protein was transferred onto Nitrocellulose membranes in transfer buffer (25 mM Tris-HCl pH 7.5, 192 mM Glycine, 20% Methanol) at 120 mA for 1 h. Protein transfer was assessed through staining with Ponceau Red for 5 min, following two washes with TBS-T. Blocking of membranes was done for 1 h at room temperature with 5% BSA in PBS. Dilutions of primary antibodies were prepared in PBS+5% BSA and membranes were incubated over night at 4° C. Following three washes for 5 min with TBS-T, dilutions of appropriate HRP-coupled secondary antibodies were prepared in PBS+5% BSA and membranes were incubated for 45 min at room temperature. After washing three times for 5 min with TBS-T, ECL detection reagent (Sigma; RPN2209) was applied and membranes were exposed to ECL Hyperfilms (Sgima; GE28-9068-37) to detect chemoluminescent signals.
Antibodies:
IncuCyte: IncuCyte automated longitudinal imaging was performed in 96 wells black walls plates (Greiner). 300,000 cells per plate were seeded to reach optimal confluence at the end of the experiment. GSK126 was aliquoted using a D300e, whereas TGFB1+2 were manually aliquoted to each well. Both were refreshed every second day. The last timepoint was independently verified using a plate reader (BMC Clariostar).
CRISPRi screen: For the CRISPRi screens, A549-MGT #1±GSK126±Dox cells were sorted on an Astrios Moflo. We aimed at a library representation of 1000× (>6 million cells) in the 10% of the lowest (dim) and 10% of the highest (bright) cells within each population. The mid population was also sorted and included in the screen analysis, as control. Cells were lysed 10′ at 56 C in AL+ProteinaseK buffer (Quiagen) followed by DNA extractionwas extracted using AMPure beads (Agencourt) and RNAse A treatment. PCR amplification and barcode-tagging of the CRISPRi libraries was done essentially as described, including PCR buffer composition77. For each sample, in PCR1, we used 20 ug of DNA divided over 10 parallel reactions, including from input controls, whereas the plasmid library needed 0.1 ng of DNA in PCR1. Parallel PCR1 reactions were mixed together and 5 ul were used as template for PCR2. We used Phusion Polymerase (NEB), GC buffer and 3% DMSO in both PCR1 and PCR2. Primers are available upon request.
Libraries concentrations were measured and barcoded libraries were pooled and sequenced on an Illumina HiSeq2500 sequencing. Reads were mapped to the in silico library with a custom script (available upon request) to generate read-counts, which were subsequently used as input for Seqmonk. We used a custom genome for Seqmonk analysis (available upon request), and samples were normalized to RPM and Log transformed to generate MA plots, whereas DEseq2 at padj<0.001 was ran on raw read counts. We ran 2 independent CRISPRi screens in A549 and one additional screen in H1944.
CRISPR/Cas9 KO: A549-MGT #1 were knocked-out for CNKSR2 and ARIDIA using a Cas9 RNP Synthego kit following instructions. Electroporation was performed using a BioRad XCell in PBS and using the standard pulse for A549 cells. Optimal gRNAs from the kit were first assessed using T7E1 as well as TIDE calculation (https://tide.nki.nl/). After that, we performed bulk assessment of MGT #1 fluorescence using flow cytometry as well as low confluence plating and manual cloning picking.
Animal experiments: All mouse studies were conducted in accordance with a protocol approved by the Institutional Animal Care and Use Committee and in agreement with regulations by the European Union. Orthotopic glioma xenograft studies were conducted as previously described76 with modifications. NOD-SCID-IL2Rg/(NSG) mice were purchased from The Jackson Laboratory and maintained in specific-pathogen-free (SPF) conditions. We used male and female mice between 7-12 weeks of age.
Gene Knock-out: Gene knock-out were performed using Synthego Gene Knockout Kits. The sgRNAs were dissolved in nuclease free 1×Te buffer to a stock concentration of 30 uM. RNP complexes were formed by mixing the Cas9 nuclease-gRNAs in a ratio of 6:1. Each RNP complex was electroporated into 250K A549-MGT1#1 in 2 mm cuvettes in 1×PBS using the Biorad GenePulser xCell (150 volts, 10 ms). After electroporation the cells were cultured in RPMI supplemented with 10% Fetal Bovine Serum and 1% of penicillin/streptomycin. Approximately 7 days after electroporation g DNA was extracted using the Invisorb spin tissue isolation kit (Stratec), eluted in 50 ul of elution buffer and PCR was performed on target genes of interest using 800 to 1200 bp products centered around the gRNA target loci (primers available upon request). Knock-out efficiency was calculated using TIDE (NKI) and T7E1 assays. Individual clones were established or bulk KO cells were directly assayed by FACS using a BD LSRFortessa and FlowJo program.
A high degree of cellular and molecular heterogeneity is believed to contribute to resistance to standard therapy in solid tumors and it poses a hurdle to development of targeted approaches. Glioblastoma Multiforme (GBM) is the most common primary adult brain tumor, it is exceptionally heterogeneous and it is resistant to therapy13. GBM is also one of the cancers with the highest degree of genomic and epigenomic characterization14-16. Based on the transcriptome, GBM tumors were recurrently classified into three subtypes, with the Mesenchymal and Proneural being more often cross-validated52,53,54. Several studies debated on the correlation between subtype-specific gene expression signatures and differential response to therapy as well as overall survival of patients. This suggests that GBM subtype identities and fate changes may hold therapeutic potential. Within a GBM tumor, a predominant subtype and tumor cells with different subtype identities may coexist17,18. Moreover, tumors can change the dominant expression profile upon recurrence19,20.
Lineage tracing previously had major impact in our understanding GBM biology in mouse models, informing on—among others—the cellular origin of individual subtypes5, as well as on how aberrant homeostatic regulation may affect response to standard of care in vivo10.
In the example, we describe a systems biology approach to design a synthetic system to genetically label any cell state or transition in complex developmental and disease settings and test this system in the quest for biological principles underlying the molecular subtypes of human GBM.
First, we assumed that subtype-specific GBM genes would substantially comprise the regulatory activity required to specific the subtype identity (i.e. cis-regulatory elements). We further assumed that the transcription factor genes (TFs) expressed in each subtype would be chiefly responsible for establishing and maintaining subtype identity.
To design a genetic cassette that would intercept the minimal signaling and regulatory information, we determined the subtype-specific GBM genes with the highest fold change compared to all other subtypes from TCGA datasets16. Calling MES, CL and PN subtype-specific genes can be achieved using an arbitrary stringent cut off (i.e. >6 Log 2 FC;
To identify genomic regions bearing high intrinsic cis-regulatory potential within the subtype differentially-regulated genes (DGRs), we computed all paired frequencies for best position weight matrix (PWM) associated with TFs expressed in each subtype (
To assemble a synthetic cis-regulatory element driving a subtype-specific expression using the above-described TFBS analysis, such synthetic Locus Control Regions (sLCRs) should ideally comprise the minimal set of cis-units with the highest number (i) and diversity (ii). Ideally, at least one cis-unit composing one sLCR would also include a natural transcriptional start site (TSS), and would be placed immediately upstream the reported element (
A typical lentiviral vector carrying a sLCR such as MGT #1, drives the subtype-expression of fluorescent reporters mVenus or mCherry. To facilitate the genetic tracing in vivo, mVenus is driven to the plasma membrane (by Igk leader and platelet-derived growth factor receptor (PDGFR) transmembrane sequences tagging;
As a prototypical testing, we produced lentiviral particles in HEK293T cells with MGT #1-mVenus sLCR, and used viral particles to infect human Glioma-initiating cells with a MES genotype (MES-hGICs). Membranous mVenus expression was observed in both transient transfection as well as in stably transduced and cryosected tumorspheres (
Next, near-isogenic and characterized MES-hGICs and PN-hGICs were transduced with MGT #1 lentiviral particles. PN-hGICs bear a combination of IDH1 and TP53 point mutations, which is only found in PN GBM, whereas MES-hGICs have triple knockdown of TP53, PTEN and NF1, featuring a MES GBM background. Interestingly, we observed a minor but measurable increase in basal fluorescence in MES-hGICs, suggesting that MGT #1 reflects a basal higher intrinsic signaling in these cells (
Human GICs and GSCs are consistently propagated under “NBE” conditions, which stands for serum-free Neurobasal media supplemented with basic FGF and EGF25. We further supplement our GICs with PDGF-AA, as this is the signaling pathway most often genetically amplified in GBM26. To investigate the ground state of MES-GBM signaling using our genetic strategy, we performed a medium-throughput cytokine screening in MES-hGICs-MGT #1low and PN-hGICs-MGT #1low cells. GICs were propagated under standard conditions and reseeded them into a 384-well format. Next, GICs were stimulated with individual cytokines in biological and technical replica followed by continuous fluorescence bottom reading in a pre-defined time course experiment. In a typical experiment, we longitudinally acquired MGT #1 fluorescence emission up to 48 hours from stimulation, and then we normalized the fluorescence to the naive GICs. In line with previous reports and above-mentioned experiments, MES-hGICs-MGT #1low turned into MES-hGICs-MGT #1high in presence of TNFα signaling (
Under the same experimental conditions, a second independent reporter (MGT #2) showed consistent results (
The in vivo source for TNFα in mouse models for Glioma is believed to be the tumor microenvironment (TME), notably glioblastoma-associated microglia/monocytes (GAMs)27. TNFα expression has been also observed in hGAMs28. Interestingly, IDH1-wild type GBM infiltration by GAMs was recently correlated with NF1 deficiency and a MEG GBM subtype identity14. To provide experimental support to the hypothesis GAMs recruited to GBM would drive a MES differentiation in NF-deficient GBM cells, we performed in vitro co-culture of IDH1-wild type and NF1-depleted MES-hGICs-MGT #1dim cells with MACS-purified CD11b cells purified from a patient with GBM. Strikingly, co-culture of hGICs-MGT #1dim cells with CD11b+ hGAMs induced MGT #1 expression in presence of IL-6 stimulation (
Our data support sLCRs as a valid readout for investigating intrinsic and adaptive responses in GICs but do not exclude the possibility that this readout is largely restricted to the sole regulation of the reporter. To understand whether the reporter regulation is accompanied by a difference in cell identity, we performed immunoblotting, globlal gene expression profiling and targeted mRNA validation in MES-hGICs-MGT #1low and PN-hGICs-MGT #1low cells. Despite being propagated under the same experimental conditions, by all experimental means tested, MES-hGICs-MGT #1low and PN-hGICs-MGT #1low cells consistently showed a limited but measurable basal difference in signaling pathway activation and gene expression (
Mesenchymal Differentiation in GBM was originally described as a dominant event at recurrence after radiotherapy19 and later linked to acquired radio-resistance via TNF-driven NFKB activation20. Repeatedly, correlative evidences support a link between inflammatory signaling, EMT and radio-resistance34. To functionally test whether irradiation may induce Mesenchymal transdifferentiation in cell autonomous manner, MES-hGICs-MGT #1low and PN-hGICs-MGT #1low cells were exposed to Ionizing Radiation (IR), alone or in combination with TNFα. For this experiment, we revolved around delivering a single radiation dose of 10 Gy for two reasons: (i) we experimentally determined this to be sub lethal (alone and in combination with other treatments, including TNFα or Temozolomide; data not shown), and (ii) 10 Gy is close to the dosages experimentally proved to unleash secondary responses as a means of intrinsic radio-resistance as well as enhanced repair capacity in multiple human GSCs34,35. The residual DNA damage marker H2A phosphorylation twenty-four hours post irradiation confirmed the occurrence of both double-strand breaks and repair. However, only a minor proportion of GICs turned to a MGT #1high state from either genetic background (
The Proneural GBM is thought to represent the common GBM ancestor subtype and also to reflect an oligodendrocytic cell-of-origin26′37. Previous studies revealed that longstanding propagation in FBS affects the phenotypic identity of individual cell lines25,16. To test whether a PN sLCR would mirror the Proneural state, we decided to induce reprogramming of a FBS-driven conventional cell line into a PN-GICs using the master TFs underlying the PN identity38. To this end, we transduced either MGT #1 or PNGT #2 into the T98G cell line, which is characterized by TP53 mutations (https://portals.broadinstitute.org/ccle), which are more likely to be associated with a PN phenotype16. In line with the genotype-driven prediction, when switched from a FBS to a NBE propagation condition, T98 cells showed a basal expression of PNGT #2 but not of MGT #1 (
Overall, these experiments indicate that multiple intrinsic and external triggers known to play a critical role in GBM biology can be intercepted by an individual sLCRs in GBM cells using the systems and synthetic biology approach described herein.
The Mesenchymal transdifferentiation is a physiologic process hijacked by multiple tumors of epithelial origin39. To investigate whether our genetic tracing strategy extends beyond the GBM homeostasis, we next transduce MGT #1 into well characterized Epithelial and Mesenchymal breast cancer cells.
Tumor subtypes are genetically engraved in breast cancer cells40. Consistently, after a first round of lentiviral transduction, epithelial MCF7 cells showed lower MGT #1 expression compared to MDA-231 cells, which are believed to have undergone EMT (
Ezh2 inhibition can support Kras-driven EMT in several mouse and human lung cancer cells41. In this setting, we tested the use of sLCRs in reflecting cellular and molecular responses to biological and chemical stimuli. Consistent with previous findings, longitudinal measurement in epithelial A549 cells revealed that high MGT #1 fluorescence was cooperatively induced by the Ezh2 inhibitor GSK126 and TFGB signaling (
Epithelial lung cancer cells exposed to TGFB signaling readily changed their morphology as well as started expressing high levels of MGT #1 as gauged by flow cytometry (
To exploit Ezh2 inhibition and MGT #1 as a framework to clarify the signaling basis of EMT in NSCLC cells, we next performed a cytokine screening in GSK126- and vehicle-treated A549-MGT #1low cells. In keeping with above-mentioned data and our recently published observations (Serresi et al., J. Exp. Med, 2018, doi:10.1084/jem.20180801), TNFα proved to be the leading signaling towards MGT #1 expression also in epithelial lung cancer cells, with a modest additive effect of GSK126 to the overall high fluorescence output measured in a longitudinal medium-throughput microplate reader screening. Simultaneously, we confirmed that A549 cells respond to TLR stimulation via bacterial LPS differently when GSK126 is present and —also under these experimental conditions—we show that TGFB1 induces MGT #1 more substantially when combined with GSK126. The systematical analysis of the screening with several cytokines and their combinations reveals that Ezh2 inhibition enhances the transcriptional response to external signaling towards EMT (
Next, we wished to exploit Ezh2 inhibition and MGT #1 as a framework for high-throughput screening to clarify the genetic basis of EMT in NSCLC cells. First, we transduced both A549 and H1944 Kras-driven NSCLC cells with the MGT #1 reporter. Subsequently, we introduced in both cell lines a Tet-inducible KRAB-dCas9 and a library of sgRNAs targeting the full complement of the human kinome (543 genes, 5,901 gRNAs in total; ˜5 gRNAs/gene). Moreover, we also included essential and non-essential genes targeting gRNAs to serve as control for the screening procedure. This system allows the systematic knock-down of individual genes in individual cells (
Taken together, the results obtained with the Epithelial-Mesenchymal transition in three different cancer types underscore the tissue-independent ability of our sLCRs to reveal tumor such homeostates.
Having demonstrated the utility of sLCRs in the dissection of cellular and molecular states ex vivo, we next wished to test the role for MGT #1 as a genetic tracing reporter for tumor homeostates in vivo. We intracranially transplanted MES-hGICs-MGT #1dim cells into NSG mice and longitudinally monitored tumor formation. At the onset of neurological signs of high-grade disease stage, we sacrificed the animals and performed histochemical and immunohistochemical as well as endogenous and surface marker analyses. Histologically, all tumors appeared as grade IV GBM, with a large proportion of mouse brain infiltrated by malignant cells, indicating extensive proliferation and invasion (
Given that response to virus, chromatin modification and gene silencing may all potentially affect sLCR expression, to confirm that MGT #1 reflect functional intratumoral heterogeneity and rule out that the MGT #1 expressing cells are simply escapers, we used two approaches. First, we inspected all the dense areas in which MES GBM signaling was absent for expression of other markers as well as of the MGT #1-independent H2B-CFP. We confirmed that the vast majority of the stained tumor tissue was accessible to antigens in immunostaining by means of Tubulin staining and we confirmed that several MGT #1 “dark” cells in which active proliferation could be inferred by chromatin condensation were indeed H2B-CFP positive (
Overall, our experiments underscore the ability of the sLCRs to illustrate intratumoral heterogeneity (
Further Experiments to Demonstrate the Feasibility and Implementation of the Invention:
sLCRs are designed to mimic endogenous CREs such as the alpha-globin LCR, which shows position-independent-cell-type- and developmental-stage-specific expression and engages transcription factories. These elements are often defined as super-enhancers and condensate into coactivator puncta. To test whether sLCRs share features with the endogenous LCRs, we measured nascent RNA in MGT #1-transduced cells by RNA-FISH and searched for BRD4 or MED1 condensates using IF. Dual IF and RNA-FISH identified co-localization between BRD4 or MED1 and the nascent RNA of MGT #1 in fixed MGT #1-expressing tumor cells (
Next, we transduced Proneural (PNGT #1-2) and Mesenchymal (MGT #1-2) sLCRs lentiviral particles into spontaneously immortalized human neural progenitor cells that acquired high copy number of PDGFRA, c-Myc and CDK4. To recapitulate the common PN and MES GBM genetic backgrounds, we further engineered hGICs to be depleted of PTEN and either bear IDH1R132 and TP53R273H point mutations or be further depleted of TP53 and NF1, thereby generating PN-hGICs and MES-hGICs, respectively. These cells show DNA methylation profiles similar to GBM patients and acquire subtype-specific gene-expression in vivo and therefore represent two distinct GBM subtypes. Under growth-factor defined conditions in vitro, PNGT #1-2 showed strong expression in both cell types, whereas MGT #1-2 displayed an overall low expression in both genotypes, underscoring the design specificity towards different regulatory networks. Of note, MGT #1 had higher basal expression in MES-hGICs compared to PN-hGICs, indicating a genotype-specific response (
Thus, we devised a method to systematically generate synthetic LCRs reflecting a given cell identity while preserving critical features of endogenous CREs.
To investigate adaptive responses to external signaling in MES-hGICs-MGT #1low and PN-hGICs-MGT #1low cells, we next performed a phenotypic screening. NBE-propagated hGICs were stimulated with selected factors (cytokines, growth factors, compounds) and FACS analyzed 48 hours after stimulation (
The observation that pro-differentiation signaling (i.e. Human serum or FBS) drives reporter activation is consistent with previous findings showing that a MES-GBM signature could be attributed to FBS cultured astroglial cells but not to any of the mouse brain cells. Of note, washout experiments suggest that the MES-GBM state is reversible within the timeframe of few days (
Mesenchymal trans-differentiation in GBM was discovered as a dominant event at recurrence after standard of care and linked to acquired radio-resistance via TNF-driven NFkB activation. A link between inflammatory signaling, EMT, innate immune cells infiltration and radio-resistance is supported by substantial correlative evidence. To experimentally test whether irradiation can induce mesenchymal trans-differentiation in cell autonomous manner, MES-hGICs-MGT #1low and PN-hGICs-MGT #1low cells were exposed to Ionizing Radiation (IR), alone or in combination with TNFα. MGT #1 activation showed a dose-response to increasing IR, whether single or fractionated dose (
Canonical NFkB activation can occur downstream TNFα signaling as well as by non-canonical genotoxic stress. To provide experimental support to the importance of the NFkB in intrinsic and acquired MES-GBM states, we deleted p65IRELA using CRISPR/Cas9 in MES-hGICs, which resulted in marked downregulation of intrinsic MGT #1 expression (
In patients, the GBM stem cell state is dominant to the genetic repertoire in maintaining tumor homeostasis. Next, we wished to test whether sLCRs can be used to discover genes that regulate the MES GBM state by performing a genome-wide pooled CRISPR/Cas9 screen. The genetic screen in MES-hGICs-MGT #1low was performed in their naïve state or when the MES-GBM state was induced by external signaling or genotoxic stress (i.e. FBS+ TNFalpha or TNZ+IR, respectively;
Overall, these results provide experimental evidence for the Mesenchymal GBM to be a transient and reversible cellular state and support robustness and effectiveness of the designed sLCRs in phenotypic screening applications.
Primary cancer types can be grouped together based on their molecular profile. Chromatin accessibility is the strongest predictor of cancer type similarity and can be used to identify subtype identities within the common dimensional space of individual cancer types. To investigate whether the acquired heterogeneity depicted by sLCRs is accompanied by changes in genome-wide chromatin accessibility, we performed ATAC-seq on MES-hGICs-MGT #1high cells in vitro and in vivo. Differential analysis of chromatin accessibility uncovered many genes undergoing remodeling, notably at driver of PN-to-MES transition WWTR1 (TAZ) and at several TNF receptor gene loci, indicating that genetic tracing for remodeling events that exclusively occur in a physiologically relevant tumor microenvironment (
IDH1-wild type GBM infiltration by Glioblastoma-associated microglia/monocytes (GAMs) was recently correlated with NF1 deficiency and a MES-GBM subtype identity but whether there is causal relationship between GAM and MES-GBM remains unresolved. To experimentally test the hypothesis that innate immune cells are causal to rather than being recruited by MES trans-differentiation in NF1-deficient GBM cells, we performed in vitro co-culture of IDH1-wild type and NF1-depleted MES-hGICs-MGT #1low cells with an immortalized human microglia cell line (hMG; cl. C20).
First, we compared the expression of both PN- and MES-sLCR expression by single cells in GBM tumorspheres and multicellular organoid culture conditions. Whereas spheroid culture supports the expansion of stem and progenitor cells with limited spontaneous differentiation and cell death50,51, glioma organoids give raise to phenotypically diverse cell populations. Resembling the in vivo expression pattern (
Next, we set up a co-culture between homogeneous GBM tumorspheres and hMG cells using trans-well insets. Strikingly, hMG cells drove MGT #1 induction in MES-hGICs to an extent comparable to TNFα (
EMT has been linked to resistance to chemotherapy but also offers therapeutic opportunities. DNA damage stress is the main therapeutic component of the standard of care in GBM, otherwise referred to as the Stupp protocol. A TNF-NFkB signature in GBM was previously linked to the mesenchymal state and radio-resistance in a large cohort of patients and PDX models. Thus, we next exploited sLCRs' ability to identify a MES homeostate in order to explore the therapeutic implications of the microglia-driven GBM state
To this end, we FACS-sorted MGT #1-2high and MGT #1-2low MES- and PN-hGICs cells after hMG-driven conversion and exposed these cells to a selected set of standard and targeted chemotherapeutics. Strikingly, in contrast to their sLCR-low counterpart. both MES-hGICs-MGT #1high or -MGT #2high cells proved to be more resistant to DNA damage-based therapeutics (Olaparib, ATR inhibitor VE-821, Topotecan, Mitomycin C) and LXR623, an LXR agonist regulating cholesterol efflux. (
Collectively, our results casually link the innate immune cells to a MES-GBM state and highlight the potential for sLCR to mechanistically dissect relevant non-cell autonomous interactions in vivo and ex vivo.
Our understanding of complex cellular and molecular mechanisms at organismal level currently rests largely on in vivo experiments and is limited by the available technologies for genetic tracing. We have established a systems biology framework that allows generating synthetic reporters capable of intercepting cell intrinsic and non-cell autonomous signaling. These sLCRs can be used to illustrate genotype-to-molecular and cellular phenotype transitions in vitro and in vivo. Experimentally, sLCR may be used in characterizing molecular mechanisms linking biological, chemical and environmental stimuli to cell fate transitions, including through chemical and forward genetic screens.
We have applied this approach to investigate cellular and molecular features of GBM subtype expression profiles. The identification of Proneural and Mesenchymal GBM subtype has been consistent across expression platform (microarrays, RNA-seq), readouts (gene expression, DNA methylation) and patients' populations (Western and Chinese). Despite such an extensive effort, GBM subtypes' significance remains elusive when it comes to their origin, location or spatiotemporal evolution.
By combining near-isogenic models and a MES sLCR, we show that the most significant component to the MES-GBM specification is adaptive in nature. Despite a genotype-instructed intrinsic MES signaling exemplified by MES-hGICs showing a measurable but moderate difference in expression of a MES sLCRs when compared to PN-hGICs, TNF signaling as well as pro-differentiation stimuli (e.g. FBS) are major triggers of MES signaling. Interestingly, TNFα and FBS both trigger MES trans-differentiation by differentially impacting cell morphology. Both kind of responses appear to be engraved in vivo, as inferred by the extent of heterogeneity in MGT #1 expression and markers of undifferentiated and self-renewing tumor cells. Our experiments link the MGT #1 readout in GBM cells to the expression of migration-associated markers such as CD44, response to pro-inflammatory microenvironment and resistance to sub-lethal doses of genotoxic stress, all of which represent the hallmarks of tumor progression, including in GBM at single cell levels18. These findings illustrate the power of MGT #1 to elucidate cellular and molecular mechanisms in GBM.
This technology enables transforming cellular and molecular profiling into phenotypic maps, which may fulfill the experimental needs associated with the continuous mapping of cellular and molecular features in health and disease, including at single-cell level. In fact, sLCR improve in vivo phenotypic assays that still represent obligatory steps towards the full understanding of complex cellular and molecular mechanisms at organismal level. As such, it offers significant ex vivo opportunities.
We show that sLCRs reflecting in vivo regulatory networks accurately intercepted cell intrinsic and non-cell autonomous signaling and were successfully applied to dissect genotype-to-molecular and cellular phenotype transitions in vitro and in vivo. We demonstrate the utility of this system by investigating the cellular and molecular basis of GBM subtype expression profiles. The identification of Proneural and Mesenchymal GBM subtype has been consistent across expression platform (microarrays, RNA-seq and single-cell RNA-seq), readouts (gene expression, DNA methylation) and patients' ethnicity (Western and Chinese). Despite such an extensive effort, significance of GBM subtypes remains elusive when it comes to their origin, location or spatiotemporal evolution and—more importantly—to their therapeutic significance.
The Proneural and Mesenchymal GBM programs rely on the activity of specific transcription factors. Here, we integrated near-isogenic models and cell lines with sLCRs and the results are consistent with the PN-GBM being the default GBM entity that strongly depends on RTK signaling and is therefore promoted by neural stem cells culture conditions. Instead, we show that the most significant component to the MES-GBM specification is adaptive in nature. In absence of a tumor microenvironment, the PN state appears hardwired even in cells with MEG-GBM genotype (e.g. NF1 depletion) but the MES identity is swiftly amplified by acute inflammatory and pro-differentiation stimuli (e.g. TNF signaling as well as bovine or human serum). Interestingly, in different cell types, MES trans-differentiation measured by sLCRs can occur along with differentially impacting cell morphology. Our experiments link MES-sLCRs readout in GBM cells, feed-forward responses to pro-inflammatory microenvironment, resistance to sub-lethal doses of genotoxic stress and expression of migration-associated markers such as CD44, all of which represent the hallmarks of progression in human cancer, including in GBM at single cell levels. These features appear to be engraved in tissue homeostasis, as inferred by clustered cellular expression pattern (‘homeostases’) and heterogeneity in tumor models in vivo and ex vivo.
Genetic tracing of MES-GBM principle components in three different cancer types underscores the tissue-independent ability of our sLCRs to reveal tumor homeostates and provides further evidence that EMT represents hijacking of a developmental cellular process. These findings illustrate the versatility of sLCRs in elucidating cellular and molecular mechanisms in multifactorial diseases. Further, the use of sLCRs in pharmacogenomics could significantly accelerate translational medicine by uncovering phenotype-specific dependencies and resistance.
Finally, sLCR enabled the mechanistic dissection of the pathophysiologically relevant non-cell autonomous interactions between innate immune cells and tumor cells. GAMs are believed to constitute the source for TNFα in both glioma mouse models and human tumors. Our results provide experimental support to the clinical association between the MES-GBM subtype and specific immune landscapes and uncover TNFα-independent routes to MES GBM. Importantly, the GAM-driven MES-GBM state herewith identified shows an extent of overlap with patients' signatures, which is comparable to that of individual patients' signature themselves.
In summary, sLCR were shown to be of use in characterizing molecular mechanisms by linking biological, chemical and environmental stimuli to cell fate transitions, including through chemical and genetic screens. Previous attempts to generate synthetic reporters using massively parallel sequencing or mixed models revealed the potential use of this approach and the limitations associated with limited control over the design. Our method substantially addressed this problem and represent a base for future development, ranging from the linear improvement on basic design components (e.g. using curated resources of TFBS and cis-elements) to the systematic generation and validation of large numbers sLCR followed by machine learning of successful features. In parallel, robust cell-type- or state-specificity and granularity may be extended by combining sLCR with DNA barcoding. Tunable operations may be achieved by coupling sLCRs transcriptional inputs with synthetic effector proteins enabling Boolean logic outputs. Thus, genetic tracing by sLCRs is scalable and can be extended to virtually any given system, whether ex vivo or in vivo to dissect cell intrinsic and non-cell autonomous mechanisms controlling normal and diseased homeostasis.
Lgr5. Nature 449, 1003-1007 (2007).
| Number | Date | Country | Kind |
|---|---|---|---|
| 18192715.3 | Sep 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/073711 | 9/5/2019 | WO | 00 |
