Patent Application
20190376060
The present invention relates in general to methods of modulating expression of a target nucleic acid sequence in a cell such as by using a compact AAV CRISPR system.
Methods of modulating expression of a target nucleic acid sequence in a cell are known. The CRISPR-Cas system has recently been developed as a flexible tool for modulating expression of target nucleic acid sequences in a cell. In one regard, the RNA-guided bacterial nuclease Cas9 can be reengineered as a programmable transcription factor by a series of modifications to the Cas9 protein including the direct fusion of modified Cas9 protein to a synthetic transcriptional activation domain (AD).1-5 However, the modest levels of gene activation achieved by the first generation Cas9 activators have limited their potential applications.6,7 A versatile, improved transcriptional regulator through the rational design of a tripartite activator, VP64-p65-RTA (VPR), fused to Cas9 was developed.8 This Cas9-tripartite activator has been demonstrated in activating expression of endogenous coding and non-coding genes, such as in stimulating neuronal differentiation of induced pluripotent stem cells (iPSCs), and having the ability to target several genes simultaneously.
Numerous zinc fingers (ZFs) and transcriptional activator like effectors (TALEs) have been fused to effector domains in order to programmably target and activate, repress, or epigenetically modify endogenous genes, laying the foundation for precision regulation of epigenetic state9-16. Unfortunately, inefficient production pipelines prevent widespread use of these tools. For example, ZFs engineered to target an arbitrary sequence must be constructed in large oligonucleotide pool arrays that are expensive, labor-intensive to generate, and are not guaranteed to be specific to the intended sequence17,18. Similarly, TALEs, while a powerful platform, pose a significant challenge for assembly, sequence verification, and genetic stability due to their highly repetitive nature. Modern methods have managed to automate labor-intensive steps of construction19. Yet, even with an automated approach, the construction of a TALE library designed to target every protein coding locus in the human genome would require over 1 million dollars and 200 days19.
Recently discovered, CRISPR-Cas systems have provided a quantum leap forward for programmable DNA-binding tools. In nature, CRISPR-Cas systems serve as archaeal and bacterial immune systems20-25. Although five different types of CRISPR-Cas systems have been discovered to date, the type II system has almost exclusively been used due to the small number of components required for DNA-targeting26. Programmable DNA-targeting by the type II CRISPR-Cas system only requires three components: Cas9 nuclease, CRISPR RNA (crRNA), and trans-activating crRNA (tracrRNA)27-30.
To initiate programmed DNA targeting, Cas9 binds both crRNA and tracrRNA in an RNA-duplex. The first 20 nucleotides of the crRNA guide Cas9 to cleave any complementary genomic sequence located next to a short protospacer adjacent motif (PAM)31,32. A convenient fusion of the crRNA and tracrRNA produces a chimeric single guide RNA (sgRNA) that is sufficient to target Cas9 as well.27
Sequence specific sgRNAs are quick and easy to construct33, and scaling up to produce tens of thousands of sgRNAs is a straightforward process. Today, a library of sgRNAs targeting every protein coding locus in the human genome can be constructed via chip-based oligonucleotide synthesis for roughly 5 thousand dollars, within a few weeks33-35. As such, the two component Cas9 and sgRNA system has been adopted as the standard genome editing tool for a wide range of organisms27,36,37.
Following the widespread adoption of Cas9 as a programmable tool for genome editing, mutated Cas9 involving residues in DNA cleavage located within each of two nuclease domains of Cas9 have been developed2,27. Mutation of these catalytic residues generated a nuclease-null ‘dead’ Cas9 (dCas9) variant, disabling its ability to cleave DNA, while retaining the ability to bind DNA in a sequence specific manner. Fusion of the dCas9 protein to effector domains, such as transcription enhancing factors, repressors, and epigenetic modulators, has enabled unprecedented ease of eukaryotic transcriptome and epigenome manipulation.
Beyond applications to cellular programming, Cas9 transcriptional and epigenetic activators hold tremendous promise for in vivo gain of function studies as well as therapeutics. However, the most convenient and only approved vector for human delivery is the Adeno-associated Virus (AAV). This convenient virus allows for targeting of various tissue types with high efficiency and little risk of integration or immunogenicity. Unfortunately, the virus is limited to a genomic payload of 4.7 kb, which can be pushed to 5 kb but not much further. The most commonly used Cas9 ortholog from S. pyogenes is 4.2 kb alone, leaving very little room for an additional promoter let alone an sgRNA expression cassette or accessory activation domains. Therefore, there is a continuing need for efficient methods and effective vector systems that allow precise manipulation of transcriptional and epigenetic state of a target nucleic acid sequence in a cell.
According to one aspect, the present disclosure provides a method of modulating expression of a target nucleic acid sequence in a cell. In one embodiment, the method includes introducing into the cell a nucleic acid sequence encoding a Cas9 protein and a guide RNA, wherein the Cas9 protein and the guide RNA are expressed and co-localize at a target site and modulate the expression of the target nucleic acid sequence. According to another aspect, a method of modulating expression of a target nucleic acid sequence in a cell is provided. In one embodiment, the method comprises introducing into the cell a nucleic acid sequence encoding a Cas9 fusion protein and a guide RNA, wherein the Cas9 fusion protein comprises Cas9 fused with at least one modified activation domain of VP64, p65 or RTA, or Cas9 fused with a combination of at least two modified activation domains of VP64, p65 and RTA, wherein the Cas9 fusion protein and the guide RNA are expressed and co-localize at a target site and modulate the expression of the target nucleic acid sequence.
In some embodiments, the Cas9 protein comprises Cas9 orthologs from Streptococcus pyogenes (Sp), Streptococcus thermophiles (St1), and Staphylococcus aureus (Sa). In one embodiment, the guide RNA is a chimeric single guide RNA (sgRNA). In an exemplary embodiment, the Cas9 protein is further fused with a transcriptional regulator. In some embodiments, the transcriptional regulator comprises a transcriptional activator, a transcriptional repressor or an epigenetic modifier. In other embodiments, the transcriptional activator comprises functional domains of multiple activators fused together. In some embodiments, the transcriptional activator comprises functional domains of VP64, p65, RTA or their various fusion combinations. In an exemplary embodiment, the transcriptional activator is a tripartite VP64-p65-RTA (VPR) activator. In some embodiments, the Cas9 is a Cas9 nickase or a nuclease null Cas9 (dCas9). In one embodiment, expression of Cas9 protein is inducible. In one embodiment, the Cas9 coding sequence is flanked by a promoter sequence at its 5′ end and a terminator sequence at its 3′ end. In an exemplary embodiment, the nucleic acid sequence encoding the Cas9 protein and the guide RNA are included on a single vector. In one embodiment, the single vector is packaged in a recombinant AAV (rAAV). In some embodiments, expression of a plurality of target nucleic acid sequences can be modulated. In one embodiment, the promoter sequence is truncated to reduce its length. In some embodiments, the promoter sequence comprises SCP1 (Super Core Promoter 1) promoter, EFS (Elongation Factor Short) promoter, or a CMV (Cytomegalovirus) promoter. In other embodiments, the terminator sequence is truncated to reduce its length. In some embodiments, the terminator sequence comprises a short 17nt sNRP-1, a 34nt dual sNRP-1, a 50nt synthetic, or a 250 nt bGHR terminator. In some embodiments, the rAAV is tissue specific. In one embodiment, the cell is from an embryo. In other embodiments, the cell is a stem cell, zygote, or a germ line cell. In some embodiments, the stem cell is an embryonic stem cell or pluripotent stem cell. In one embodiment, the cell is a somatic cell. In another embodiment, the somatic cell is a eukaryotic cell. In one embodiment, the eukaryotic cell is an animal cell.
In certain embodiments, the nucleic acid sequence encoding the Cas9 fusion protein and the guide RNA are included on a single vector that is capable of being packaged into a recombinant AAV (rAAV). In other embodiments, the activation domain of VP64, p65 or RTA is modified by truncation to reduce length while retaining activity as a transcriptional activator. In certain other embodiments, the combination of modified activation domains of VP64, p65 and RTA comprises a tripartite VP64-p65-RTA (VPR) fusion wherein each of the activation domains of VP64, p65 and RTA is truncated. In one embodiment, the Cas9 is a nuclease null Cas9 (dCas9). In another embodiment, expression of the Cas9 fusion protein is inducible. In one embodiment, the Cas9 fusion protein coding sequence is flanked by a promoter sequence at its 5′ end and a terminator sequence at its 3′ end. In another embodiment, expression of a plurality of target nucleic acid sequences can be modulated. In one embodiment, the promoter sequence is truncated to reduce its length suitable for packaging into an rAAV. In exemplary embodiments, the promoter sequence comprises SCP1 (Super Core Promoter 1) promoter (SEQ ID NO: 33), EFS (Elongation Factor Short) promoter (SEQ ID NO: 34), or a CMV (Cytomegalovirus) promoter. In certain embodiments, the terminator sequence is truncated to reduce its length suitable for packaging into an rAAV. In other embodiments, the terminator sequence comprises a short 17nt sNRP-1 (SEQ ID NO: 35), a 34nt dual sNRP-1 (SEQ ID NO: 36), a 50nt synthetic (SEQ ID NO: 37), or a 250 nt bGHR terminator.
According to another aspect, the present disclosure provides a nucleic acid construct comprises nucleic acid sequences encoding a Cas9 protein and a guide RNA. In one embodiment, the guide RNA is a chimeric single guide RNA (sgRNA). In some embodiments, the Cas9 protein is further fused with a transcriptional regulator. In other embodiments, the transcriptional regulator comprises a transcriptional activator, a transcriptional repressor or an epigenetic modifier. In some embodiments, the transcriptional activator comprises functional domains of multiple activators fused together. In other embodiments, the transcriptional activator comprises functional domains of VP64, p65, RTA or their various fusion combinations. In an exemplary embodiment, the transcriptional activator is a tripartite VP64-p65-RTA (VPR) activator. In one embodiment, the Cas9 is a Cas9 nickase or a nuclease null Cas9 (dCas9). In exemplary embodiment, the Cas9 coding sequence is flanked by a promoter sequence at its 5′ end and a terminator sequence at its 3′ end. In certain embodiments, the promotor sequence is truncated to reduce its length. In other embodiments, the promoter sequence comprises SCP1 (Super Core Promoter 1) promoter, EFS (Elongation Factor Short) promoter, or a CMV (Cytomegalovirus) promoter. In some embodiments, the terminator sequence is truncated to reduce its length. In other embodiments, the terminator sequence comprises a short 17nt sNRP-1, a 34nt dual sNRP-1, a 50nt synthetic, or a 250 nt bGHR terminator. In one embodiment, the guide RNA and/or the Cas9 fusion protein is introduced into the cell.
According to still another aspect, the present disclosure provides a recombinant AAV (rAAV) comprising a nucleic acid construct comprising the nucleic acid sequences encoding the Cas9 protein and the guide RNA according to the embodiments of the disclosure. In some embodiments, the rAAV is tissue specific.
According to one aspect, the target nucleic acid sequence of the present disclosure includes genomic DNA, mitochondrial DNA, viral DNA, or exogenous DNA.
According to another aspect, the present disclosure provides a method of treating a disease of a subject comprising administering a therapeutically effective amount of a recombinant AAV(rAAV) in the subject in need thereof. In one embodiment, the rAAV comprises a nucleic acid sequence encoding a Cas9 protein or a Cas9 fusion protein and a guide RNA. In another embodiment, the Cas9 protein is fused with a transcriptional regulator and the guide RNA comprises complementary sequences to a target site. In one embodiment, the Cas9 fusion protein and the guide RNA are expressed and co-localize at a target site and modulate the expression of a target gene. In another embodiment, the transcriptional regulator comprises a transcriptional activator, a transcriptional repressor or an epigenetic modifier. In an exemplary embodiment, the transcriptional activator is a tripartite VP64-p65-RTA (VPR) activator. In one embodiment, the Cas9 is a nuclease null Cas9 (dCas9). In one embodiment, the disease is a monogenetic disease. In some embodiments, the monogenetic disease includes monogenetic muscle wasting diseases. In other embodiments, the monogenetic muscle wasting diseases comprise Nemaline Myopathy, Duchenne Muscular Dystrophy, and McArdle's Disease. In some embodiments, the target gene comprises the cardiac actin gene, the utrophin gene, and the brain glycogen phosphorylase gene. In other embodiments, expression of cardiac actin gene, utrophin gene, or brain glycogen phosphorylase gene of the subject is modulated.
According to one aspect, a nucleic acid construct is provided. In one embodiment, the nucleic acid construct comprises nucleic acid sequences encoding a Cas9 fusion protein and a guide RNA. In another embodiment, the guide RNA is a chimeric single guide RNA (sgRNA). In certain embodiments, the Cas9 fusion protein comprises Cas9 fused with at least one modified activation domain of VP64, p65 or RTA, or Cas9 fused with a combination of at least two modified activation domains of VP64, p65 and RTA. In some embodiments, the activation domain of VP64, p65 or RTA is modified by truncation to reduce length while retaining activity as a transcriptional activator. In certain embodiments, the combination of modified activation domains of VP64, p65 and RTA comprises a tripartite VP64-p65-RTA (VPR) fusion wherein each of the activation domains of VP64, p65 and RTA is truncated. In one embodiment, the Cas9 is a nuclease null Cas9 (dCas9). In other embodiment, the Cas9 fusion protein coding sequence is flanked by a promoter sequence at its 5′ end and a terminator sequence at its 3′ end. In certain embodiments, the promotor sequence is truncated to reduce its length suitable for packaging into an rAAV. In exemplary embodiments, the promoter sequence comprises a Super Core Promoter 1 (SCP1) (SEQ ID NO: 33), an Elongation Factor Short (EFS) promoter (SEQ ID NO: 34), or a Cytomegalovirus (CMV) promoter. In other embodiments, the terminator sequence is truncated to reduce its length suitable for packaging into an rAAV. In exemplary embodiments, the terminator sequence comprises a short 17nt sNRP-1 (SEQ ID NO: 35), a 34nt dual sNRP-1 (SEQ ID NO: 36), a 50nt synthetic (SEQ ID NO: 37), or a 250 nt bGHR terminator. In one embodiment, the modified activation domain of VP64 is encoded by nucleic acid sequence of SEQ ID NO: 1. In certain embodiments, the modified activation domain of p65 is encoded by nucleic acid sequence of SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, or SEQ ID NO: 10, respectively. In other embodiments, the modified activation domain of RTA is encoded by nucleic acid sequence of SEQ ID NO: 3, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, or SEQ ID NO: 16, respectively.
According to one other aspect, a recombinant AAV comprising a nucleic acid comprising nucleic acid sequences encoding a Cas9 fusion protein and a guide RNA according to the various embodiments as disclosed herein is provided. In one embodiment, the AAV is tissue specific.
In one embodiment, the modified activation domain of VP64 comprises protein sequence of SEQ ID NO: 17, which is encoded by nucleic acid sequence of SEQ ID NO: 1. In another embodiment, the modified activation domain of p65 comprises p65 deletion protein. In certain embodiments, the p65 deletion protein comprises protein sequence of SEQ ID NO: 18, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, or SEQ ID NO: 26, which are encoded by nucleic acid sequence of SEQ ID NO: 2, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, or SEQ ID NO: 10, respectively. In one embodiment, the modified activation domain of RTA comprises RTA deletion protein. In certain embodiments, the RTA deletion protein comprises protein sequence of SEQ ID NO: 19, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 31, or SEQ ID NO: 32, which are encoded by nucleic acid sequence of SEQ ID NO: 3, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, or SEQ ID NO: 16, respectively.
In some embodiments, the Cas9 fusion protein comprises the activation domain of VP64 or its variants, the activation domain of p65 or its deletion variants, and/or the activation domain of RTA or its deletion variants.
Further features and advantages of certain embodiments of the present invention will become more fully apparent in the following description of embodiments and drawings thereof, and from the claims.
The foregoing and other features and advantages of the present embodiments will be more fully understood from the following detailed description of illustrative embodiments taken in conjunction with the accompanying drawings in which:
Embodiments of the present disclosure provides methods and systems for modulating expression of a target nucleic acid sequence in a cell. According to one aspect, the present disclosure provides CRISPR based DNA targeting tools. In exemplary embodiments, a nucleic acid sequence encoding a Cas9 protein and a guide RNA is provided on a single vector, such as an engineered DNA plasmid vector. This vector is then packaged into a recombinant adeno-associated virus (rAAV) for delivery of the nucleic acid sequence encoding the Cas9 protein and the guide RNA into the desired cells or tissues. According to another aspect, the Cas9 is fused with transcriptional regulators or epigenetic modifiers. Once delivered into the cell, the Cas9 or Cas9 fusion protein and the guide RNA are expressed. The guide RNA comprises portion that is complementary to a sequence of a target site and guides the Cas9 or Cas9 fusion protein to the target site where expression of a target nucleic acid sequence can be modulated. Since the Cas9 will cleave the target nucleic acid sequence, a nuclease null Cas9 (dCas9) is employed to form fusion protein with a transcriptional regulator or an epigenetic modifier. In this manner, expression of the target nucleic acid sequence is modulated depending on the specific transcriptional regulator or epigenetic modifier fused with the dCas9. In one embodiments, the transcriptional regulator is a transcriptional activator. In another embodiment, the transcriptional regulator is a transcriptional repressor. In still another embodiment, the transcriptional regulator is an epigenetic modifier. In some embodiments, the transcriptional activator can be engineered to include functional domains of multiple activators fused together. In exemplary embodiments, the transcriptional activator includes functional domains of VP64, p65, RTA, or their various fusion combinations. In an exemplary embodiment, the transcriptional activator is a tripartite VP64-p65-RTA (VPR) activator.
Due to the payload size limit of the nucleic acid sequence that can be packaged into a rAAV, it is desirable to reduce the size of each of the component of the CRISPR system. In certain embodiments, the present disclosure provides that the small Cas9 orthologs are used. For example, small Cas9 orthologs from Streptococcus thermophiles (St1)46 and Staphylococcus aureus (Sa)49 are used in addition to the common Cas9 from Streptococcus pyogenes (Sp)28. According to one aspect, the Cas9 protein includes the sequence as set forth for naturally occurring Cas9 from S. thermophiles (St1), S. aureus (Sa) or S. pyogenes (Sp) and protein sequences having at least 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98% or 99% homology thereto. Small Cas9 can also be engineered so that the non-essential regions of Cas9 is deleted while the functional regions of Cas9 is retained. Such engineering methods are known to a skilled in the art. According to one aspect, the engineered small Cas9 protein includes deletions or mutations of the naturally occurring Cas 9 (wild type) having protein sequences having at least 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98% or 99% homology to the naturally occurring Cas9 from S. thermophiles (St1), S. aureus (Sa) or S. pyogenes (Sp) sequences as set forth. In other embodiments, the guide RNA can be reduced in size using engineering methods known to a skilled in the art. In an exemplary embodiment, a small sized chimeric single guide RNA (sgRNA) is employed46, 49, 28. According to one aspect, the guide RNA can be engineered from naturally occurring guide RNA sequence to reduce in size so that the non-essential regions of the guide RNA is deleted while the functional regions of the guide RNA is retained. The engineered small sized guide RNA include nucleic acid sequences having at least 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98% or 99% homology to the naturally occurring guide RNA counterpart known in the art. The present disclosure provides engineered small guide RNAs that are used in a single vector with the nucleic acid sequence encoding the Cas9 protein for packaging into a rAAV. In some embodiments, the sizes of the promoter sequence and the terminator sequence flanking the Cas9 coding sequence are reduced for fitting into the rAAV. As used herein, a “promoter” refers to a control region of a nucleic acid sequence at which initiation and rate of transcription of the remainder of a nucleic acid sequence are controlled. A promoter may also contain sub-regions at which regulatory proteins and molecules may bind, such as RNA polymerase and other transcription factors. Promoters may be constitutive, inducible, activatable, repressible, tissue-specific or any combination thereof. A promoter drives expression or drives transcription of the nucleic acid sequence that it regulates. As used herein, a promoter is considered to be “operably linked” when it is in a correct functional location and orientation in relation to a nucleic acid sequence it regulates to control (“drive”) transcriptional initiation and/or expression of that sequence. A promoter may be classified as strong or weak according to its affinity for RNA polymerase (and/or sigma factor); this is related to how closely the promoter sequence resembles the ideal consensus sequence for the polymerase. The strength of a promoter may depend on whether initiation of transcription occurs at that promoter with high or low frequency. Different promoters with different strengths may be used to engineer nucleic acids with different levels of gene/protein expression (e.g., the level of expression initiated from a weak promoter is lower than the level of expression initiated from a strong promoter). A promoter may be one naturally associated with a gene or sequence, as may be obtained by isolating the 5′ non-coding sequences located upstream of the coding segment of a given gene or sequence. Such a promoter can be referred to as “endogenous.” In some embodiments, “non-naturally occurring” promoter may be used. Such promoters may include promoters of other genes; promoters isolated from any other cell; and synthetic promoters or enhancers such as those that contain different elements of different transcriptional regulatory regions and/or mutations that alter expression through methods of genetic engineering that are known in the art. In some embodiments, small sized promoters may be used to fit into the packaging AAV. In other embodiments, short tissue specific promoters, either naturally occurring or engineered, may be used to optimize the delivery vectors and constructs for downstream in vivo applications. In some embodiments, the promoter sequence comprises an SCP1 (Super Core Promoter 1) promoter (SEQ ID NO: 33), an EFS (Elongation Factor Short) promoter (SEQ ID NO: 34), or a CMV (Cytomegalovirus) promoter. Other engineered or synthetic promoters of small size can also be used. According to one aspect, the engineered or synthetic promoters of small size include nucleic acid sequences having at least 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98% or 99% homology to the SCP1 promoter (SEQ ID NO: 33) and EFS promoter (SEQ ID NO: 34), respectively. In other embodiments, the terminator sequence is truncated to reduce its length. In some embodiments, the terminator sequence comprises a short 17nt sNRP-1 (SEQ ID NO: 35), a 34nt dual sNRP-1 (SEQ ID NO: 36), a 50nt synthetic (SEQ ID NO: 37), or a 250 nt bGHR terminator. Other engineered or synthetic terminator sequences of small size can also be used. According to one aspect, the engineered or synthetic terminator sequences of small size include nucleic acid sequences having at least 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98% or 99% homology to the short 17nt sNRP-1 (SEQ ID NO: 35), 34nt dual sNRP-1 (SEQ ID NO: 36), or 50nt synthetic (SEQ ID NO: 37), respectively.
According to another aspect, the present disclosure provides a single nucleic acid construct that includes the nucleic acid sequences encoding the Cas9 or Cas9 fusion protein and the guide RNA. In one embodiment, the single nucleic acid construct is an AAV expression plasmid vector which can be packaged into a rAAV according to methods known to a skilled in the art.
According to still another aspect, the present disclosure provides a recombinant AAV (rAAV) comprising a nucleic acid construct comprising the nucleic acid sequences encoding the Cas9 or Cas9 fusion protein and the guide RNA according to the embodiments of the disclosure. The present disclosure provides that the rAAV used is not limited to a certain type. Any type of AAV can be used based on the desired tissue or cell specificity. While AAV is able to infect many different cell or tissue types, the infection efficiency varies based upon serotype, which is determined by the sequence of the capsid protein. The present disclosure provides that native AAV serotypes 1-9 and engineered AAV systems such as AAV-DJ and AAV-DJ/8 can be used to provide tissue specific delivery of the compact CRISPR system according to the disclosure.
According to one aspect, the target nucleic acid sequence of the present disclosure includes genomic DNA, mitochondrial DNA, viral DNA, or exogenous DNA.
RNA guided DNA binding proteins are readily known to those of skill in the art to bind to DNA for various purposes. Such DNA binding proteins may be naturally occurring. DNA binding proteins having nuclease activity are known to those of skill in the art, and include naturally occurring DNA binding proteins having nuclease activity, such as Cas9 proteins present, for example, in Type II CRISPR systems. Such Cas9 proteins and Type II CRISPR systems are well documented in the art. See Makarova et al., Nature Reviews, Microbiology, Vol. 9, June 2011, pp. 467-477 including all supplementary information hereby incorporated by reference in its entirety.
In general, bacterial and archaeal CRISPR-Cas systems rely on short guide RNAs in complex with Cas proteins to direct degradation of complementary sequences present within invading foreign nucleic acid. See Deltcheva, E. et al. CRISPR RNA maturation by trans-encoded small RNA and host factor RNase III. Nature 471, 602-607 (2011); Gasiunas, G., Barrangou, R., Horvath, P. & Siksnys, V. Cas9-crRNA ribonucleoprotein complex mediates specific DNA cleavage for adaptive immunity in bacteria. Proceedings of the National Academy of Sciences of the United States of America 109, E2579-2586 (2012); Jinek, M. et al. A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity. Science 337, 816-821 (2012); Sapranauskas, R. et al. The Streptococcus thermophilus CRISPR/Cas system provides immunity in Escherichia coli. Nucleic acids research 39, 9275-9282 (2011); and Bhaya, D., Davison, M. & Barrangou, R. CRISPR-Cas systems in bacteria and archaea: versatile small RNAs for adaptive defense and regulation. Annual review of genetics 45, 273-297 (2011). A recent in vitro reconstitution of the S. pyogenes type II CRISPR system demonstrated that crRNA (“CRISPR RNA”) fused to a normally trans-encoded tracrRNA (“trans-activating CRISPR RNA”) is sufficient to direct Cas9 protein to sequence-specifically cleave target DNA sequences matching the crRNA. Expressing a gRNA homologous to a target site results in Cas9 recruitment and degradation of the target DNA. See H. Deveau et al., Phage response to CRISPR-encoded resistance in Streptococcus thermophilus. Journal of Bacteriology 190, 1390 (February, 2008).
Three classes of CRISPR systems are generally known and are referred to as Type I, Type II or Type III). According to one aspect, a particular useful enzyme according to the present disclosure to cleave dsDNA is the single effector enzyme, Cas9, common to Type II. See K. S. Makarova et al., Evolution and classification of the CRISPR-Cas systems. Nature reviews. Microbiology 9, 467 (June, 2011) hereby incorporated by reference in its entirety. Within bacteria, the Type II effector system consists of a long pre-crRNA transcribed from the spacer-containing CRISPR locus, the multifunctional Cas9 protein, and a tracrRNA important for gRNA processing. The tracrRNAs hybridize to the repeat regions separating the spacers of the pre-crRNA, initiating dsRNA cleavage by endogenous RNase III, which is followed by a second cleavage event within each spacer by Cas9, producing mature crRNAs that remain associated with the tracrRNA and Cas9. TracrRNA-crRNA fusions are contemplated for use in the present methods.
According to one aspect, the enzyme of the present disclosure, such as Cas9 unwinds the DNA duplex and searches for sequences matching the crRNA to cleave. Target recognition occurs upon detection of complementarity between a “protospacer” sequence in the target DNA and the remaining spacer sequence in the crRNA. Importantly, Cas9 cuts the DNA only if a correct protospacer-adjacent motif (PAM) is also present at the 3′ end. According to certain aspects, different protospacer-adjacent motif can be utilized. For example, the S. pyogenes system requires an NGG sequence, where N can be any nucleotide. S. thermophilus Type II systems require NGGNG (see P. Horvath, R. Barrangou, CRISPR/Cas, the immune system of bacteria and archaea. Science 327, 167 (Jan. 8, 2010) hereby incorporated by reference in its entirety and NNAGAAW (see H. Deveau et al., Phage response to CRISPR-encoded resistance in Streptococcus thermophilus. Journal of bacteriology 190, 1390 (February, 2008) hereby incorporated by reference in its entirety), respectively, while different S. mutans systems tolerate NGG or NAAR (see J. R. van der Ploeg, Analysis of CRISPR in Streptococcus mutans suggests frequent occurrence of acquired immunity against infection by M102-like bacteriophages. Microbiology 155, 1966 (June, 2009) hereby incorporated by refernece in its entirety. Bioinformatic analyses have generated extensive databases of CRISPR loci in a variety of bacteria that may serve to identify additional useful PAMs and expand the set of CRISPR-targetable sequences (see M. Rho, Y. W. Wu, H. Tang, T. G. Doak, Y. Ye, Diverse CRISPRs evolving in human microbiomes. PLoS genetics 8, e1002441 (2012) and D. T. Pride et al., Analysis of streptococcal CRISPRs from human saliva reveals substantial sequence diversity within and between subjects over time. Genome research 21, 126 (January, 2011) each of which are hereby incorporated by reference in their entireties.
In S. pyogenes, Cas9 generates a blunt-ended double-stranded break 3 bp upstream of the protospacer-adjacent motif (PAM) via a process mediated by two catalytic domains in the protein: an HNH domain that cleaves the complementary strand of the DNA and a RuvC-like domain that cleaves the non-complementary strand. See Jinek et al., Science 337, 816-821 (2012) hereby incorporated by reference in its entirety. Cas9 proteins are known to exist in many Type II CRISPR systems including the following as identified in the supplementary information to Makarova et al., Nature Reviews, Microbiology, Vol. 9, June 2011, pp. 467-477: Methanococcus maripaludis C7; Corynebacterium diphtheriae; Corynebacterium efficiens YS-314; Corynebacterium glutamicum ATCC 13032 Kitasato; Corynebacterium glutamicum ATCC 13032 Bielefeld; Corynebacterium glutamicum R; Corynebacterium kroppenstedtii DSM 44385; Mycobacterium abscessus ATCC 19977; Nocardia farcinica IFM10152; Rhodococcus erythropolis PR4; Rhodococcus jostii RHA1; Rhodococcus opacus B4 uid36573; Acidothermus cellulolyticus 11B; Arthrobacter chlorophenolicus A6; Kribbella flavida DSM 17836 uid43465; Thermomonospora curvata DSM 43183; Bifidobacterium dentium Bd1; Bifidobacterium longum DJO10A; Slackia heliotrinireducens DSM 20476; Persephonella marina EX H1; Bacteroides fragilis NCTC 9434; Capnocytophaga ochracea DSM 7271; Flavobacterium psychrophilum JIP02 86; Akkermansia muciniphila ATCC BAA 835; Roseiflexus castenholzii DSM 13941; Roseiflexus RS1; Synechocystis PCC6803; Elusimicrobium minutum Pei191; uncultured Termite group 1 bacterium phylotype Rs D17; Fibrobacter succinogenes S85; Bacillus cereus ATCC 10987; Listeria innocua; Lactobacillus casei; Lactobacillus rhamnosus GG; Lactobacillus salivarius UCC118; Streptococcus agalactiae A909; Streptococcus agalactiae NEM316; Streptococcus agalactiae 2603; Streptococcus dysgalactiae equisimilis GGS 124; Streptococcus equi zooepidemicus MGCS10565; Streptococcus gallolyticus UCN34 uid46061; Streptococcus gordonii Challis subst CH1; Streptococcus mutans NN2025 uid46353; Streptococcus mutans; Streptococcus pyogenes M1 GAS; Streptococcus pyogenes MGAS5005; Streptococcus pyogenes MGAS2096; Streptococcus pyogenes MGAS9429; Streptococcus pyogenes MGAS10270; Streptococcus pyogenes MGAS6180; Streptococcus pyogenes MGAS315; Streptococcus pyogenes SSI-1; Streptococcus pyogenes MGAS10750; Streptococcus pyogenes NZ131; Streptococcus thermophiles CNRZ1066; Streptococcus thermophiles LMD-9; Streptococcus thermophiles LMG 18311; Clostridium botulinum A3 Loch Maree; Clostridium botulinum B Eklund 17B; Clostridium botulinum Ba4 657; Clostridium botulinum F Langeland; Clostridium cellulolyticum H10; Finegoldia magna ATCC 29328; Eubacterium rectale ATCC 33656; Mycoplasma gallisepticum; Mycoplasma mobile 163K; Mycoplasma penetrans; Mycoplasma synoviae 53; Streptobacillus moniliformis DSM 12112; Bradyrhizobium BTAi1; Nitrobacter hamburgensis X14; Rhodopseudomonas palustris BisB18; Rhodopseudomonas palustris BisB5; Parvibaculum lavamentivorans DS-1; Dinoroseobacter shibae DFL 12; Gluconacetobacter diazotrophicus Pal 5 FAPERJ; Gluconacetobacter diazotrophicus Pal 5 JGI; Azospirillum B510 uid46085; Rhodospirillum rubrum ATCC 11170; Diaphorobacter TPSY uid29975; Verminephrobacter eiseniae EF01-2; Neisseria meningitides 053442; Neisseria meningitides alpha14; Neisseria meningitides Z2491; Desulfovibrio salexigens DSM 2638; Campylobacter jejuni doylei 269 97; Campylobacter jejuni 81116; Campylobacter jejuni; Campylobacter lari RM2100; Helicobacter hepaticus; Wolinella succinogenes; Tolumonas auensis DSM 9187; Pseudoalteromonas atlantica T6c; Shewanella pealeana ATCC 700345; Legionella pneumophila Paris; Actinobacillus succinogenes 130Z; Pasteurella multocida; Francisella tularensis novicida U112; Francisella tularensis holarctica; Francisella tularensis FSC 198; Francisella tularensis tularensis; Francisella tularensis WY96-3418; and Treponema denticola ATCC 35405. The Cas9 protein may be referred by one of skill in the art in the literature as Csn1. An exemplary S. pyogenes Cas9 protein sequence is provided in Deltcheva et al., Nature 471, 602-607 (2011) hereby incorporated by reference in its entirety.
Modification to the Cas9 protein is contemplated by the present disclosure. CRISPR systems useful in the present disclosure are described in R. Barrangou, P. Horvath, CRISPR: new horizons in phage resistance and strain identification. Annual review of food science and technology 3, 143 (2012) and B. Wiedenheft, S. H. Sternberg, J. A. Doudna, RNA-guided genetic silencing systems in bacteria and archaea. Nature 482, 331 (Feb. 16, 2012) each of which are hereby incorporated by reference in their entireties.
According to certain aspects, the DNA binding protein is altered or otherwise modified to inactivate the nuclease activity. Such alteration or modification includes altering one or more amino acids to inactivate the nuclease activity or the nuclease domain. Such modification includes removing the polypeptide sequence or polypeptide sequences exhibiting nuclease activity, i.e. the nuclease domain, such that the polypeptide sequence or polypeptide sequences exhibiting nuclease activity, i.e. nuclease domain, are absent from the DNA binding protein. Other modifications to inactivate nuclease activity will be readily apparent to one of skill in the art based on the present disclosure. Accordingly, a nuclease-null DNA binding protein includes polypeptide sequences modified to inactivate nuclease activity or removal of a polypeptide sequence or sequences to inactivate nuclease activity. The nuclease-null DNA binding protein retains the ability to bind to DNA even though the nuclease activity has been inactivated. Accordingly, the DNA binding protein includes the polypeptide sequence or sequences required for DNA binding but may lack the one or more or all of the nuclease sequences exhibiting nuclease activity. Accordingly, the DNA binding protein includes the polypeptide sequence or sequences required for DNA binding but may have one or more or all of the nuclease sequences exhibiting nuclease activity inactivated.
According to one aspect, a DNA binding protein having two or more nuclease domains may be modified or altered to inactivate all but one of the nuclease domains. Such a modified or altered DNA binding protein is referred to as a DNA binding protein nickase, to the extent that the DNA binding protein cuts or nicks only one strand of double stranded DNA. When guided by RNA to DNA, the DNA binding protein nickase is referred to as an RNA guided DNA binding protein nickase. An exemplary DNA binding protein is an RNA guided DNA binding protein nuclease of a Type II CRISPR System, such as a Cas9 protein or modified Cas9 or homolog of Cas9. An exemplary DNA binding protein is a Cas9 protein nickase. An exemplary DNA binding protein is an RNA guided DNA binding protein of a Type II CRISPR System which lacks nuclease activity. An exemplary DNA binding protein is a nuclease-null or nuclease deficient Cas9 protein.
According to an additional aspect, nuclease-null Cas9 proteins are provided where one or more amino acids in Cas9 are altered or otherwise removed to provide nuclease-null Cas9 proteins. According to one aspect, the amino acids include D10 and H840. See Jinek et al., Science 337, 816-821 (2012). According to an additional aspect, the amino acids include D839 and N863. According to one aspect, one or more or all of D10, H840, D839 and H863 are substituted with an amino acid which reduces, substantially eliminates or eliminates nuclease activity. According to one aspect, one or more or all of D10, H840, D839 and H863 are substituted with alanine. According to one aspect, a Cas9 protein having one or more or all of D10, H840, D839 and H863 substituted with an amino acid which reduces, substantially eliminates or eliminates nuclease activity, such as alanine, is referred to as a nuclease-null Cas9 (“Cas9Nuc”) and exhibits reduced or eliminated nuclease activity, or nuclease activity is absent or substantially absent within levels of detection. According to this aspect, nuclease activity for a Cas9Nuc may be undetectable using known assays, i.e. below the level of detection of known assays.
According to one aspect, the Cas9 protein, Cas9 protein nickase or nuclease null Cas9 includes homologs and orthologs thereof which retain the ability of the protein to bind to the DNA and be guided by the RNA. According to one aspect, the Cas9 protein includes the sequence as set forth for naturally occurring Cas9 from S. thermophiles, S. aureus or S. pyogenes and protein sequences having at least 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98% or 99% homology thereto and being a DNA binding protein, such as an RNA guided DNA binding protein.
An exemplary CRISPR system includes the S. thermophiles or S. aureus Cas9 nuclease (ST1 Cas9, Sa Cas9) (see Esvelt K M, et al., Orthogonal Cas9 proteins for RNA-guided gene regulation and editing, Nature Methods., (2013) hereby incorporated by reference in its entirety). An exemplary CRISPR system includes the S. pyogenes Cas9 nuclease (Sp. Cas9), an extremely high-affinity (see Sternberg, S. H., Redding, S., Jinek, M., Greene, E. C. & Doudna, J. A. DNA interrogation by the CRISPR RNA-guided endonuclease Cas9. Nature 507, 62-67 (2014) hereby incorporated by reference in its entirety), programmable DNA-binding protein isolated from a type II CRISPR-associated system (see Garneau, J. E. et al. The CRISPR/Cas bacterial immune system cleaves bacteriophage and plasmid DNA. Nature 468, 67-71 (2010) and Jinek, M. et al. A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity. Science 337, 816-821 (2012) each of which are hereby incorporated by reference in its entirety). According to certain aspects, a nuclease null or nuclease deficient Cas 9 can be used in the methods described herein. Such nuclease null or nuclease deficient Cas9 proteins are described in Gilbert, L. A. et al. CRISPR-mediated modular RNA-guided regulation of transcription in eukaryotes. Cell 154, 442-451 (2013); Mali, P. et al. CAS9 transcriptional activators for target specificity screening and paired nickases for cooperative genome engineering. Nature biotechnology 31, 833-838 (2013); Maeder, M. L. et al. CRISPR RNA-guided activation of endogenous human genes. Nature methods 10, 977-979 (2013); and Perez-Pinera, P. et al. RNA-guided gene activation by CRISPR-Cas9-based transcription factors. Nature methods 10, 973-976 (2013) each of which are hereby incorporated by reference in its entirety. The DNA locus targeted by Cas9 (and by its nuclease-deficient mutant, “dCas9” precedes a three nucleotide (nt) 5′-NGG-3′ “PAM” sequence, and matches a 15-22-nt guide or spacer sequence within a Cas9-bound RNA cofactor, referred to herein and in the art as a guide RNA. Altering this guide RNA is sufficient to target Cas9 or a nuclease deficient Cas9 to a target nucleic acid. In a multitude of CRISPR-based biotechnology applications (see Mali, P., Esvelt, K. M. & Church, G. M. Cas9 as a versatile tool for engineering biology. Nature methods 10, 957-963 (2013); Hsu, P. D., Lander, E. S. & Zhang, F. Development and Applications of CRISPR-Cas9 for Genome Engineering. Cell 157, 1262-1278 (2014); Chen, B. et al. Dynamic imaging of genomic loci in living human cells by an optimized CRISPR/Cas system. Cell 155, 1479-1491 (2013); Shalem, O. et al. Genome-scale CRISPR-Cas9 knockout screening in human cells. Science 343, 84-87 (2014); Wang, T., Wei, J. J., Sabatini, D. M. & Lander, E. S. Genetic screens in human cells using the CRISPR-Cas9 system. Science 343, 80-84 (2014); Nissim, L., Perli, S. D., Fridkin, A., Perez-Pinera, P. & Lu, T. K. Multiplexed and Programmable Regulation of Gene Networks with an Integrated RNA and CRISPR/Cas Toolkit in Human Cells. Molecular cell 54, 698-710 (2014); Ryan, O. W. et al. Selection of chromosomal DNA libraries using a multiplex CRISPR system. eLife 3 (2014); Gilbert, L. A. et al. Genome-Scale CRISPR-Mediated Control of Gene Repression and Activation. Cell (2014); and Citorik, R. J., Mimee, M. & Lu, T. K. Sequence-specific antimicrobials using efficiently delivered RNA-guided nucleases. Nature biotechnology (2014) each of which are hereby incorporated by reference in its entirety), the guide is often presented in a so-called sgRNA (single guide RNA), wherein the two natural Cas9 RNA cofactors (gRNA and tracrRNA) are fused via an engineered loop or linker.
According to one aspect, the Cas9 protein is an enzymatically active Cas9 protein, a Cas9 protein wild-type protein, a Cas9 protein nickase or a nuclease null or nuclease deficient Cas9 protein. Additional exemplary Cas9 proteins include Cas9 proteins attached to, bound to or fused with functional proteins such as transcriptional regulators, such as transcriptional activators or repressors, a Fok-domain, such as Fok 1, an aptamer, a binding protein, PP7, MS2 or an epigenetic modifier and the like.
According to certain aspects, the Cas9 protein may be delivered directly to a cell by methods known to those of skill in the art, including injection or lipofection, or as translated from its cognate mRNA, or transcribed from its cognate DNA into mRNA (and thereafter translated into protein). Cas9 DNA and mRNA may be themselves introduced into cells through electroporation, transient and stable transfection (including lipofection) and viral transduction or other methods known to those of skill in the art. In exemplary embodiments, Cas9 coding DNA sequence is packaged into rAAV and delivered to cells in vivo or in vitro.
Embodiments of the present disclosure are directed to the use of a CRISPR/Cas system and, in particular, a guide RNA which may include one or more of a spacer sequence, a tracr mate sequence and a tracr sequence. The term spacer sequence is understood by those of skill in the art and may include any polynucleotide having sufficient complementarity with a target nucleic acid sequence to hybridize with the target nucleic acid sequence and direct sequence-specific binding of a CRISPR complex to the target sequence. The guide RNA may be formed from a spacer sequence covalently connected to a tracr mate sequence (which may be referred to as a crRNA) and a separate tracr sequence, wherein the tracr mate sequence is hybridized to a portion of the tracr sequence. According to certain aspects, the tracr mate sequence and the tracr sequence are connected or linked such as by covalent bonds by a linker sequence, which construct may be referred to as a fusion of the tracr mate sequence and the tracr sequence. The linker sequence referred to herein is a sequence of nucleotides, referred to herein as a nucleic acid sequence, which connect the tracr mate sequence and the tracr sequence. Accordingly, a guide RNA may be a two component species (i.e., separate crRNA and tracr RNA which hybridize together) or a unimolecular species (i.e., a crRNA-tracr RNA fusion, often termed an sgRNA).
According to certain aspects, the guide RNA is between about 10 to about 500 nucleotides. According to one aspect, the guide RNA is between about 20 to about 100 nucleotides. According to certain aspects, the spacer sequence is between about 10 and about 500 nucleotides in length. According to certain aspects, the tracr mate sequence is between about 10 and about 500 nucleotides in length. According to certain aspects, the tracr sequence is between about 10 and about 100 nucleotides in length. According to certain aspects, the linker nucleic acid sequence is between about 10 and about 100 nucleotides in length.
According to one aspect, embodiments described herein include guide RNA having a length including the sum of the lengths of a spacer sequence, tracr mate sequence, tracr sequence, and linker sequence (if present). Accordingly, such a guide RNA may be described by its total length which is a sum of its spacer sequence, tracr mate sequence, tracr sequence, and linker sequence (if present). According to this aspect, all of the ranges for the spacer sequence, tracr mate sequence, tracr sequence, and linker sequence (if present) are incorporated herein by reference and need not be repeated. A guide RNA as described herein may have a total length based on summing values provided by the ranges described herein. Aspects of the present disclosure are directed to methods of making such guide RNAs as described herein by expressing constructs encoding such guide RNA using promoters and terminators and optionally other genetic elements as described herein.
According to certain aspects, the guide RNA may be delivered directly to a cell as a native species by methods known to those of skill in the art, including injection or lipofection, or as transcribed from its cognate DNA, with the cognate DNA introduced into cells through electroporation, transient and stable transfection (including lipofection) and viral transduction. In exemplary embodiments, guide RNA coding sequence is packaged into rAAV and delivered to cells in vivo or in vitro.
According to one aspect, an engineered Cas9-gRNA system is provided which enables RNA-guided DNA regulation in cells by tethering transcriptional activation/repression domains to either a nuclease-null Cas9 or to guide RNAs. According to one aspect of the present disclosure, one or more transcriptional regulatory proteins or domains (such terms are used interchangeably) are joined or otherwise connected to a nuclease-deficient Cas9 or one or more guide RNA (gRNA). The transcriptional regulatory domains correspond to targeted loci. Accordingly, aspects of the present disclosure include methods and materials for localizing transcriptional regulatory domains to targeted loci by fusing, connecting or joining such domains to either Cas9N or to the gRNA.
Foreign nucleic acids (i.e. those which are not part of a cell's natural nucleic acid composition) may be introduced into a cell using any method known to those skilled in the art for such introduction. Such methods include transfection, transduction, viral transduction, microinjection, lipofection, nucleofection, nanoparticle bombardment, transformation, conjugation and the like. One of skill in the art will readily understand and adapt such methods using readily identifiable literature sources. Foreign nucleic acid sequence may include donor nucleic acid sequence. The term “donor nucleic acid” include a nucleic acid sequence which is to be inserted into genomic DNA according to methods described herein. The donor nucleic acid sequence may be expressed by the cell. According to one aspect, the donor nucleic acid is exogenous to the cell. According to one aspect, the donor nucleic acid is foreign to the cell.
Cells according to the present disclosure include any cell into which foreign nucleic acids can be introduced and expressed as described herein. It is to be understood that the basic concepts of the present disclosure described herein are not limited by cell type. In some embodiments, the cell is from an embryo. The cell can be a stem cell, zygote, or a germ line cell. In embodiments where the cell is a stem cell, the stem cell is an embryonic stem cell or pluripotent stem cell. In other embodiments, the cell is a somatic cell. In embodiments, where the cell is a somatic cell, the somatic cell is a eukaryotic cell or prokaryotic cell. The eukaryotic cell can be an animal cell, such as from a pig, mouse, rat, rabbit, dog, horse, cow, non-human primate, human.
Vectors are contemplated for use with the methods and constructs described herein. The term “vector” includes a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. Vectors used to deliver the nucleic acids to cells as described herein include vectors known to those of skill in the art and used for such purposes. Certain exemplary vectors may be plasmids, lentiviruses or adeno-associated viruses known to those of skill in the art. Vectors include, but are not limited to, nucleic acid molecules that are single-stranded, doublestranded, or partially double-stranded; nucleic acid molecules that comprise one or more free ends, no free ends (e.g. circular); nucleic acid molecules that comprise DNA, RNA, or both; and other varieties of polynucleotides known in the art. One type of vector is a “plasmid,” which refers to a circular double stranded DNA loop into which additional DNA segments can be inserted, such as by standard molecular cloning techniques. Another type of vector is a viral vector, wherein virally-derived DNA or RNA sequences are present in the vector for packaging into a virus (e.g. retroviruses, lentiviruses, replication defective retroviruses, adenoviruses, replication defective adenoviruses, and adeno-associated viruses). Viral vectors also include polynucleotides carried by a virus for transfection into a host cell. Certain vectors are capable of autonomous replication in a host cell into which they are introduced (e.g. bacterial vectors having a bacterial origin of replication and episomal mammalian vectors). Other vectors (e.g., non-episomal mammalian vectors) are integrated into the genome of a host cell upon introduction into the host cell, and thereby are replicated along with the host genome. Moreover, certain vectors are capable of directing the expression of genes to which they are operatively linked. Such vectors are referred to herein as “expression vectors.” Common expression vectors of utility in recombinant DNA techniques are often in the form of plasmids. Recombinant expression vectors can comprise a nucleic acid of the invention in a form suitable for expression of the nucleic acid in a host cell, which means that the recombinant expression vectors include one or more regulatory elements, which may be selected on the basis of the host cells to be used for expression, that is operatively-linked to the nucleic acid sequence to be expressed. Within a recombinant expression vector, “operably linked” is intended to mean that the nucleotide sequence of interest is linked to the regulatory element(s) in a manner that allows for expression of the nucleotide sequence (e.g. in an in vitro transcription/translation system or in a host cell when the vector is introduced into the host cell).
Methods of non-viral delivery of nucleic acids or native DNA binding protein, native guide RNA or other native species include lipofection, microinjection, biolistics, virosomes, liposomes, immunoliposomes, polycation or lipid:nucleic acid conjugates, naked DNA, artificial virions, and agent-enhanced uptake of DNA. Lipofection is described in e.g., U.S. Pat. Nos. 5,049,386, 4,946,787; and 4,897,355) and lipofection reagents are sold commercially (e.g., Transfectam™ and Lipofectin™). Cationic and neutral lipids that are suitable for efficient receptor-recognition lipofection of polynucleotides include those of Felgner, WO 91/17424; WO 91/16024. Delivery can be to cells (e.g. in vitro or ex vivo administration) or target tissues (e.g. in vivo administration). The term native includes the protein, enzyme or guide RNA species itself and not the nucleic acid encoding the species.
Regulatory elements are contemplated for use with the methods and constructs described herein. The term “regulatory element” is intended to include promoters, enhancers, internal ribosomal entry sites (IRES), and other expression control elements (e.g. transcription termination signals, such as polyadenylation signals and poly-U sequences). Such regulatory elements are described, for example, in Goeddel, GENE EXPRESSION TECHNOLOGY: METHODS IN ENZYMOLOGY 185, Academic Press, San Diego, Calif. (1990). Regulatory elements include those that direct constitutive expression of a nucleotide sequence in many types of host cell and those that direct expression of the nucleotide sequence only in certain host cells (e.g., tissue-specific regulatory sequences). A tissue-specific promoter may direct expression primarily in a desired tissue of interest, such as muscle, neuron, bone, skin, blood, specific organs (e.g. liver, pancreas), or particular cell types (e.g. lymphocytes). Regulatory elements may also direct expression in a temporal-dependent manner, such as in a cell-cycle dependent or developmental stage-dependent manner, which may or may not also be tissue or cell-type specific. In some embodiments, a vector may comprise one or more pol III promoter (e.g. 1, 2, 3, 4, 5, or more pol III promoters), one or more pol II promoters (e.g. 1, 2, 3, 4, 5, or more pol II promoters), one or more pol I promoters (e.g. 1, 2, 3, 4, 5, or more pol I promoters), or combinations thereof. Examples of pol III promoters include, but are not limited to, U6 and H1 promoters. Examples of pol II promoters include, but are not limited to, the retroviral Rous sarcoma virus (RSV) LTR promoter (optionally with the RSV enhancer), the cytomegalovirus (CMV) promoter (optionally with the CMV enhancer) [see, e.g., Boshart et al, Cell, 41:521-530 (1985)], the SV40 promoter, the dihydrofolate reductase promoter, the β-actin promoter, the phosphoglycerol kinase (PGK) promoter, and the EF1α promoter and Pol II promoters described herein. Also encompassed by the term “regulatory element” are enhancer elements, such as WPRE; CMV enhancers; the R-U5′ segment in LTR of HTLV-I (Mol. Cell. Biol., Vol. 8(1), p. 466-472, 1988); SV40 enhancer; and the intron sequence between exons 2 and 3 of rabbit (3-globin (Proc. Natl. Acad. Sci. USA., Vol. 78(3), p. 1527-31, 1981). It will be appreciated by those skilled in the art that the design of the expression vector can depend on such factors as the choice of the host cell to be transformed, the level of expression desired, etc. A vector can be introduced into host cells to thereby produce transcripts, proteins, or peptides, including fusion proteins or peptides, encoded by nucleic acids as described herein (e.g., clustered regularly interspersed short palindromic repeats (CRISPR) transcripts, proteins, enzymes, mutant forms thereof, fusion proteins thereof, etc.).
Aspects of the methods described herein may make use of terminator sequences. A terminator sequence includes a section of nucleic acid sequence that marks the end of a gene or operon in genomic DNA during transcription. This sequence mediates transcriptional termination by providing signals in the newly synthesized mRNA that trigger processes which release the mRNA from the transcriptional complex. These processes include the direct interaction of the mRNA secondary structure with the complex and/or the indirect activities of recruited termination factors. Release of the transcriptional complex frees RNA polymerase and related transcriptional machinery to begin transcription of new mRNAs. Terminator sequences include those known in the art and identified and described herein.
Aspects of the methods described herein may make use of epitope tags and reporter gene sequences. Non-limiting examples of epitope tags include histidine (His) tags, V5 tags, FLAG tags, influenza hemagglutinin (HA) tags, Myc tags, VSV-G tags, and thioredoxin (Trx) tags. Examples of reporter genes include, but are not limited to, glutathione-S-transferase (GST), horseradish peroxidase (HRP), chloramphenicol acetyltransferase (CAT) beta-galactosidase, betaglucuronidase, luciferase, green fluorescent protein (GFP), HcRed, DsRed, cyan fluorescent protein (CFP), yellow fluorescent protein (YFP), and autofluorescent proteins including blue fluorescent protein (BFP).
Embodiments of the present disclosure are directed to a method of delivering a nucleic acid sequence encoding the Cas9 protein and guide RNA to cells within a subject comprising administering to the subject, such as systemically administering to the subject, such as by intravenous administration or injection, intraperitoneal administration or injection, intramuscular administration or injection, intracranial administration or injection, intraocular administration or injection, subcutaneous administration or injection, the nucleic acid sequence that is packaged in rAAV.
Diseases and detrimental conditions may be characterized by abnormal loss of expression or underexpression of a particular protein or abnormal gain or overexpression of a particular protein. Such diseases or detrimental conditions can be treated by upregulation or down regulation of the particular protein. Accordingly, methods of treating a disease or detrimental condition are provided where the co-localization complex as described herein associates or otherwise binds to target DNA including a target nucleic acid, and the transcriptional activator of the co-localization complex upregulates expression of the target nucleic acid or the transcriptional repressor of the co-localization complex downregulates expression of the target nucleic acid. One of skill in the art will readily identify such diseases and detrimental conditions associated with target DNA based on the present disclosure.
Mutations in genomic DNA are known to result in alteration and pathological development in cellular function and diseases, as well as cancer, diabetes, cardiovascular diseases, neurodegenerative disorders, aging or genetic disorders (See, Alexeyev M. et al., The Maintenance of Mitochondrial DNA Integrity—Critical Analysis and Update, Cold Spring Harb Perspect Biol, (2013); 5:a012641). Accordingly, methods of treating a disease or detrimental condition are provided where foreign DNA is integrated into a target nucleic acid sequence of a eukaryotic cell via providing to the cell a guide RNA sequence complementary to a target nucleic acid sequence, providing to the cell a donor sequence, providing to the cell a Cas9 enzyme that interacts with the guide RNA sequence and cleaves the target nucleic acid sequence in a site specific manner, wherein the guide RNA sequence binds to the complementary target nucleic acid sequence and the Cas9 enzyme cleaves the target mitochondrial nucleic acid sequence in a site specific manner; and wherein the donor sequence is integrated into the nucleic acid sequence. In this manner, the mutation can be corrected by the donor sequence.
The following examples are set forth as being representative of the present disclosure. These examples are not to be construed as limiting the scope of the present disclosure as these and other equivalent embodiments will be apparent in view of the present disclosure, figures and accompanying claims.
To design an enhanced activator, a small library of transcription factor ADs and members of the mediator and RNA polymerase II complexes for potential use as transcriptional effectors were screened42. More than 20 individual candidates were fused to the C-terminus of Streptococcus pyogenes (SP)-dCas9. These putative dCas9-activator constructs were transfected into mammalian cells and their potency assessed by quantifying fluorescence from a transcriptional reporter by flow cytometry2 (
1.2 Engineer Activator with Improved Efficiency Over dCas9-VP64
As neither of the most potent hybrid Cas9-ADs showed activity above the VP64 fusion, an alternative method could be found by taking advantage of the innately cooperative transcriptional mechanism which exists in nature. In natural systems, transcriptional initiation occurs through the coordinated recruitment of the necessary machinery by a group of locally concentrated transcription factor ADs44. Hence, it was hypothesized that joining multiple activation domains to a single dCas9 molecule would result in an increase in transcriptional activation by mimicking the natural cooperative recruitment process. Taking dCas9-VP64 as a starting scaffold, an additional nuclear localization signal/sequence was introduced to ensure efficient targeting. In some embodiments, the nuclear localization signal/sequence may be optimized to increase the targeting efficiency of the Cas9 and transcription activation fusion protein. The C-terminal fusion was subsequently extended with the addition of either the p65 or Rta AD. As predicted, when p65 or Rta was joined to dCas9-VP64, an increase in transcriptional output was observed. Further improvement was observed when both p65 and Rta were fused in tandem to VP64, generating a hybrid VP64-p65-Rta tripartite activator (hereinafter referred to as VPR) (
To begin characterizing VPR, the importance of each of its constituent parts (VP64, p65, and Rta) was confirmed by replacing each member with mCherry and measuring the resulting protein's activity by reporter assay. All fusions containing mCherry showed a decrease in activity relative to VPR but exhibited higher levels of activity with respect to the VP64 activation domain alone, demonstrating the essentiality of all members of the VPR complex (data not shown). While the VPR fusion showed a clear improvement in transcriptional activation, the optimal ordering of the individual ADs remained unknown. To test the role of domain order, a set of dCas9-VPR constructs was designed in which the positions of VP64, p65, and Rta were shuffled to generate all possible non-repeating rearrangements. Evaluation of the VPR permutations confirmed that the original VP64-p65-Rta order was indeed the optimal configuration (data not shown).
Having performed initial characterization of our SP-dCas9-VPR fusion, it was next sought to assess its ability to activate endogenous coding and non-coding targets relative to VP64. To this end, 3-4 gRNAs were constructed against a set of factors related to cellular reprogramming, development, and gene therapy. When compared to the dCas9-VP64 activator, dCas9-VPR showed 22-to-320 fold improved activation of endogenous targets. Induced genes include the long-noncoding RNA (lncRNA) MIAT, the largest protein-coding gene in the human genome, TTN, several transcription factors, NEUROD1, ASCL1, RHOXF2, and a structural protein, ACTC1 (
Beyond single gene activation, a primary advantage of the Cas9 system is the ability to target several loci in tandem. Cas9 enables multiplexed activation through the simple introduction of a collection of guide RNAs against a desired set of genes. To determine the efficiency of multi-gene targeting, a pooled activation experiment was performed simultaneously inducing four of our initially characterized genes MIAT, NEUROD1, ASCL1, and RHOXF2. VPR allowed for robust multi-locus activation, exhibiting several-fold higher expression levels than VP64 across the panel of genes. Despite the general performance decrease resulting from multiplex transcriptional modulation, our system still directed the induction of all targets to greater than 450-fold over their basal expression levels in the control cells (
Given the activation efficiency of our SP-dCas9-VPR fusion, it was investigated whether the VPR construct would exhibit similar potency when fused to other DNA-binding scaffolds. Fusion of VPR to a nuclease-null Streptococcus thermophilus (ST1)-dCas9, a designer transcription activator like effector (TALE), or a zinc-finger protein allowed for a respective ˜6×, ˜4×, and ˜2× increase in activation relative to VP64, as determined by a reporter assay45,46. (Data not shown.)
Given the activation efficiency of our SP-dCas9-VPR fusion in the human HEK 293T cell line, it was investigated whether the VPR construct would exhibit similar potency when targeted to genes in fly, yeast, and mouse cell lines. Targeting to Drosophila melongaster Schneider 2 (S2) cells allowed for 3300-fold up-regulation of the Cecal gene and 32,600-fold up-regulation of the Mtk gene, corresponding to a respective 300-fold and 120-fold improvement upon dCas9-VP64 activation of the same loci. Targeting to Saccharomyces cervisae enabled 96-fold up-regulation of Gal7 and 39-fold up-regulation of Hed1, corresponding to a respective 9-fold and 5-fold improvement upon dCas9-VP64 activation. Targeting to Mus musculus Neuro-2a cell (N2A) allowed for 1200-fold up-regulation above background expression level of Actc1, corresponding to a 67-fold improvement upon dCas9-VP64. Remarkably, the ultimate cardiac actin expression level induced by dCas9-VPR was 11-fold higher than mouse B-actin as measured by qPCR—an unprecedented result. (
1.7 iPSC Reprogramming to Neurons as Proof of Principle
The ability to regulate gene expression levels through transcriptional activation provides a powerful means to reprogram cellular identity for regenerative medicine and basic research purposes. Previous work has shown that the ectopic expression of several cDNAs enables cellular reprogramming of terminally differentiated cells to a pluripotent state, and can similarly induce differentiation of stem cells into multiple cell types25. While such studies typically require multiple factors, it was recently shown that exogenous expression of single transcription factors, Neurogenin2 (NGN2) or Neurogenic differentiation factor 1 (NEUROD1), is sufficient to induce differentiation of human iPS cells into induced neurons (iNeurons)47. It was previously attempted to recapitulate this same differentiation paradigm using dCas9-VP64 based activators and observed minimal differentiation activity (data not shown). It was hypothesized this was due to insufficient activation and therefore postulated that VPR might overcome this barrier and enable differentiation of iPS cells to iNeurons by more potently activating either NGN2 or NEUROD1.
Stable PGP1 iPS doxycycline-inducible dCas9-VP64 and dCas9-VPR cell lines were generated and transduced with lentiviral vectors containing a mixed pool of 30 gRNAs directed against either NGN2 or NEUROD1. To determine differentiation efficiency, gRNA containing dCas9-AD iPS cell lines were cultured in the presence of doxycycline for four days and monitored for phenotypic changes. It was observed that VPR, in contrast to VP64, enabled rapid and robust differentiation of iPS cells into a neuronal phenotype consistent with previously published reports. Additionally, these cells stained positively for the neuronal markers Beta III tubulin and neurofilament 20048. Quantification of Beta III tubulin staining revealed that dCas9-VPR cell lines showed either ˜22.5× or ˜10× improvement in the amount of iNeurons observed through activation of NGN2 or NEUROD1, respectively. Similar results were observed with neurofilament 200 staining. Analysis by qRT-PCR four days after doxycycline-induction revealed a ˜10-fold and ˜18-fold increase in mRNA expression levels for NGN2 and NEUROD1, respectively, within dCas9-VPR cells over their dCas9-VP64 counterparts (data not shown.)
2.1 Repurpose Tool with Small Staphylococcus aureus Cas9
While SpCas9 is most commonly employed for genome editing and transcriptional regulation applications, the St1 and Sa Cas9 orthologs are more suitable to in vivo applications due to their minimal size46,49. While the SpCas9 is 4.2 kb, barely able to fit in an AAV vector, the St1 ortholog is 3.4 kb, and the SaCas9 is 3.2 kb—both of which are able to comfortably fit within the size limit of AAV.
Even with the 1 kb gain in sequence space from replacing dSpCas9 with dSaCas9, the entire dSaCas9-VPR tool stands at 4.9 kb to express the activator gene alone. With the packaging limit of AAV being 4.7 kb, this tool is impossible to package, let alone with the necessary constitutive promoter (the standard is a 600 bp CMV promoter), poly adenlyation signal (the signal used to express SaCas9 for in vivo editing is the bGHR signal of 250 bp), and sgRNA expression cassette consisting of the 250 bp RNA pol II U6 promoter and 100 bp sgRNA sequence. As such, all elements required minimization. It was hypothesized that the activation domains (p65 and RTA, originally identified to build the VPR activator) could be truncated to isolate only necessary elements for activator domain function. Sliding window truncations were performed on p65 and RTA to identify several minimal domains that retained activity. Furthermore, it was hypothesized that the truncated domains might retain their ability to induce high levels of gene expression, comparable to the full length VPR activator, when fused together as a synergistic unit.
The size of the Cas9 activator was able to be reduced from the original dSpCas9-VPR tool, standing at 5.9 kb, down to a miniature yet potent dSaCas9-VPR employing the p65 (100-261aa) truncation and the RTA (125-190aa) truncation, leading to a small yet effective tool of 4.2 kb—well below the packaging limit of AAV. While the dSa-VPR miniature activator is below the packaging limit of AAV, one other activator has been identified in the literature that is below the packaging limit of AAV, and that is the dSa-VP64 activator. To confirm the relative superiority of the dSa-VPR miniature activator over the dSa-VP64 tool, both tools were targeted to a set of 4 genes and compared relative levels of induction.
While the activator tool is below the packaging limit of AAV, other elements must be incorporated into the final design. As such, several short promoters were screened, and identified two small constitutive promoters that would allow for high levels of dSa-VPR miniature expression, without compromising the tools ability to activate genes as compared to when expressed off of the gold-standard CMV promoter. The two promoters, SCP1 and EFS, are 80 and 200 bp long respectively, compared to CMV which is 600 bp in length.
Similarly, several poly adenlyation signals were screened, and identified an extremely short dual function polyadenlyation (pA) signal/stop codon that is efficient for termination of gene transcription and translation.50,51 The short 17nt terminator was previously shown to work efficiently in vivo, and a dual repeat (34nt) version was shown to work comparatively efficiently to several other polyadenlyation signals including the popular SV40 polyA sequence. The single repeat sNRP-1 polyA signal, dual repeat version, the synthetic polyA signal, and the commonly used bGHR polyA signal were compared for ability to stabilize activator transcripts and therefore enable downstream activation of targeted genes.
2.6 Activate Endogenous Genes with Single Vector System
With a small 3.2 kb Staphylococcus aureus Cas9, a 1 kb miniature yet potent VPR activator, constitutive yet unprecedentedly small 80 bp SCP1 promoter, and a novel extremely short dual function transcription and translation 34 bp 2×sNRP1 terminator, a theoretical activator expression cassette totaling just above 4.3 kb was reached—well below the packaging limit of AAV. In order to create a single vector system, all elements were combined, alongside a 350 bp sgRNA expression cassette, to create a 4.7 kb tool ready for packaging in to AAV. The new single vector cassette for the ability of all elements to efficiently work together were validated by comparing the design to the only other activator that will currently fit within the packaging limit of AAV—the dSa-VP64 tool. Due to the smaller size of the dSa-VP64 tool, full-length CMV promoter and bGHR signals, along with the sgRNA expression cassette were able to be included, making the most of the space available when using the smaller activator. Then the two single vector tools were compared for ability to activate several target genes via transfection, to validate the enhanced potency of our novel single vector activator expression system, relative to the only other small activator available using gold standard expression elements.
The new tool performs far better than the alternative standard activator tool that would be available for packaging in to an AAV expression cassette. While many applications of in vivo transcriptional regulation will undoubtedly occur in neuronal cell types, it was wished to validate the efficacy of the SCP1 promoter, the novel miniature Cas9 activator, the compact sNRP-1 terminator, and guide RNA expression system in a variety of cell lines, to confirm the relevance of the tool for use in other tissue types. Thus, our novel activator was targeted to a panel of genes in 3 additional cell lines, C2C12 mouse myocytes, GC-1 mouse spermatogonial cells, and Hepa 1-6 mouse hepatocarcinoma cells, as well as Neuro-2A cells. Since the target genes will be present in a variety of epigenetic states when targeted in different cell types, and it is possible that genomic rearrangements in immortalized cell lines might even lead to a loss of the targeted locus in a new cell line, it was not expected that all targets to be activated in every cell line. However, at least one target was activated extremely well in each cell line, validating that each element is working in all four lines, albeit at different efficiencies depending on the locus.
With the tool validated in 4 separate mouse cell lines in vitro, the new Cas9 activator expression system was packaged in to high titer AAV. AAV has 12 serotypes available for packaging, with a variety of tropisms specific to targeting a variety of tissue types including neuronal cells, muscle, liver, retinal cells, etc. However, an alternative serotype AAV-DJ has been developed, which allows for relatively efficient delivery to in vitro cell lines. In order to more rapidly validate that the tool packaged efficiently, could be delivered via AAV, and could mediate activation of target genes when packaged in AAV, it was chosen to initially package a tool targeting the mouse Actc1 gene in to AAV-DJ. To validate the packaging efficiency, the vector was titered by running qPCR on the packaged virus alongside qPCR of linearized vector standards, with defined copy numbers. Additionally, the AAV virus was denatured, and ran the packaged genomes on a 1% agarose e-gel with SYBR Gold stain, which visualizes single stranded DNA, alongside cut vector standards. a titer of roughly 10{circumflex over ( )}12 total viral particles isolated for the mActc1 targeting activator tool was detected, and it was observed a roughly 5 kb clean band on the electrophoresis gel, indicating that the vector has been correctly packaged.
To validate the packaged Actc1 targeting activator tool, packaged in AAV-DJ, the virus was delivered to C2C12, Hepa 1-6, GC-1, and Neuro-2A cells, and assayed for expression of the targeted gene.
Following in vitro activation of target genes, it was aimed to validate the tool for activation of targeted genes in vivo. A batch of AAV-9 was produced, which targets cardiac tissue, with the mHbb targeting activator. The viral yield was 2×10{circumflex over ( )}11, which is roughly 1 order of magnitude lower than typical viral prep. The pups were injected with the AAV preps, and collected heart, liver, and additional tissues a week post injection, to assay for Hbb expression. The results of this pilot experiment are shown in
3.1 Identify gRNAs for Activation of Targets with Single Vector Activator In Vitro
Aspects of the present disclosure provides methods and systems that can be used for treating diseases such as monogenetic muscle wasting diseases. In exemplary embodiments, the present disclosure provides methods and systems for activating three target genes, Cardiac actin, Utrophin, and Brain Glycogen Phosphorylase for the treatment of monogenetic muscle wasting diseases in mouse models (Nemaline Myopathy, Duchenne Muscular Dystrophy, and McArdle's Disease, respectively.) Each of these diseases is caused by a mutation in a single gene coding for either a structural or enzymatic protein; the mutations lead to non-functional alleles and loss of muscle cell integrity. However, all three genes have alternative fetal isoforms, located in distal positions within the genome that are expressed throughout gestation. In to adulthood, the fetal isoforms are silenced, and the adult isoforms are induced—if the adult isoform contains debilitating mutations, the individual begins suffering from symptoms of the muscle wasting disease. However, there is good evidence that overexpression of the original fetal isoform may be a viable therapeutic avenue, as the fetal isoform is functionally equivalent to the adult isoform—and perfectly intact (as mutations in the fetal isoform would have been lethal during gestation.) In the case of Duchenne Muscular Dystrophy, it is not possible to deliver either a fully intact copy of either DMD cDNA (a corrected version of the diseased gene) or Utrophin cDNA (the alternative isoform of the disease gene) due to the sheer size of the two genes. Thus, attempts at activating endogenous Utrophin gene expression have begun—and a small molecule aimed at inducing Utrophin in adults suffering from Duchenne Muscular Dystrophy are currently in progress. However, the levels of gene activation are suboptimal. The methods and the miniature CRISPR Cas9 activator AAV system can be developed to target each of these three genes, as a proof of principle for application in transcriptional activation based gene therapy.
A single potent gRNA for targeting of Actc1 (Cardiac Actin) was identified. Further, appropriate gRNAs for Utrn (Utrophin), or Pygb (Brain glycogen phosphorylase) will be identified. Data for Actc1 using the isolated gRNA is shown in
The single vector activator targeting Actc1 construct was packaged in AAV-DJ, as shown in
As shown in
Once the AAV6 is packaged with the activator tool targeting Actc1, it will be delivered both locally to hind limb muscle, and systemically. Mice will be assayed for over expression of the Actc1 gene in adult muscle tissue, liver, and additional organs. The same will be done with the Utrn and Pygb targeting viruses, once they are produced.
Once activation of the therapeutic target genes is validated in wild type mice in vivo, these AAV packaged constructs will be used in respective mouse disease models. The AAV packaged constructs will be delivered systemically and locally to hind limb muscle in both wild type mice as well as Acta1 knockout mice (which recapitulate the Nemaline Myopathy phenotype, and can be rescued via transgenic over expression of the Actc1 gene.) Additionally, AAV6 packaged constructs that target Utrn will be delivered to the MDX mice (knockout of the Dmd, which recapitulates the Duchenne Muscular Dystrophy phenotype) and AAV packaged with constructs targeting Pygb will be delivered to muscle glygogen phosphorylase knockout mice (recapitulates the McArdle's Disease phenotype.) The expression of the target genes will be detected in the mouse models and assessed for efficacy of disease treatment.
Aspects of the present disclosure provides methods of using the single vector CRISPR AAV based system for modulating target gene expression. CRISPR Cas9 based genetic and epigenetic regulators are known for ease of use and has broad applications. Cas9 transcriptional regulators have been used to tackle several previously challenging biological applications. These regulators have been used to deconstruct genetic networks that confer resistance phenotypes, mediate cellular differentiation by activating endogenous genes, activate latent HIV genomes to improve efficacy of antiretroviral therapy, and induce a morphological phenotype in vivo. The present disclosure thus provides for applications to genome wide screening of poorly understood classes of genes, as well as transcriptional and epigenetic paradigms for human gene therapy using the single vector CRISPR AAV based system.
According to some aspects, the present disclosure contemplates treating diseases based on the single vector CRISPR AAV based system such as using Cas9 transcriptional regulators. Diseases such as Prader-Willi and Angelman Syndrome are caused by a pathogenic deletion in one parental allele, while the other fully functional allele is silenced due to genomic imprinting (the process by which certain alleles are silenced, depending on which parent it was inherited from). In such cases, the present disclosure provides methods of Cas9 based activators in the single vector CRISPR AAV based system which can activate expression from the silenced allele, providing expression of a fully intact copy of the missing gene.
According to other aspects, the present disclosure contemplates treating monogenetic diseases based on the single vector CRISPR AAV based system such as using Cas9 transcriptional regulators. The Cas9 transcriptional regulators can mediate modest overexpression of compensatory genes for disease treatment. For example, Duchenne Muscular Dystrophy (DMD) is an X-linked disease caused by mutations in the protein Dystrophin. Pathogenic mutations disrupt the protein Dystrophin, which is responsible for anchoring a cell's actin cytoskeleton to the extracellular matrix in muscle. Since Dystrophin is located on the X chromosome, male patients only have a single copy of Dystrophin; when that copy is mutated, no functional Dystrophin is available, and muscle tissue loses its integrity causing muscle weakness and wasting. As a result, patients have difficulty with walking, respiration, and other daily activities. Currently, there are no commercialized therapies for DMD. The present disclosure provides the single vector CRISPR AAV based system for treating DMD via direct editing of genomic mutations in Dystrophin to correct the faulty sequence38,39.
An alternative approach, which has already been applied in clinical trials, is the up-regulation of a Dystrophin paralog, Utrophin, which can complement the function of mutated Dystrophin40. In clinical trials, small molecule mediated activation of expression is modest in its efficacy; direct activation of endogenous Utrophin expression with the single vector CRISPR AAV based system such as using Cas9 transcriptional activators based on the present disclosure may solve this issue in a straightforward manner. Activators may be delivered episomally via Adeno-associated virus (AAV) to muscle tissue, such as is the case with Glybera (the only approved gene therapy in the Western world, used to deliver a therapeutic gene to treat lipoprotein lipase deficiency)41. While such a method may not be a permanent cure, as the activator would not be stably integrated in to the genome of target cells, it is safer than Cas9 based genome-editing approaches that suffer from greater off-target effects, which are irreversible. Akin to Glybera, such a therapeutic may be delivered via local injection of gene therapy virus, and benefit from relatively long term expression in muscle tissue without the risk of permanent integration41.
Expanding upon this paradigm, the present disclosure contemplates applications of the single vector CRISPR AAV based system such as using Cas9 transcriptional regulators for treating many monogenetic diseases that have genes having compensatory genetic paralogs that may be activated in a similar therapeutic approach. The highly programmable nature of Cas9 regulatory tools will allow for therapies developed for a single disease to be easily repurposed for other diseases that can be treated via activation or suppression of naturally encoded beneficial genes based on the present disclosure.
Sequences for the various activation domains, promoters and terminators used herein are summarized in Tables 1 and 2.
The disclosure of each reference cited is expressly incorporated herein.
The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.
While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
This application claims priority to U.S. Provisional Application No. 62/470,538 filed on Mar. 13, 2017, which is hereby incorporated herein by reference in its entirety for all purposes.
This invention was made with government support under Grant No. 2012143331 awarded by the National Science Foundation and under Grant Nos. HG005550 and HG008525 awarded by the National Institutes of Health. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US18/22220 | 3/13/2018 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62470538 | Mar 2017 | US |
