Patent Application
20090053718
The present invention relates to ribonucleic acids and oligonucleotide probes useful for detection and analysis of microRNAs and their target mRNAs, as well as small interfering RNAs (siRNAs). The invention furthermore relates to oligonucleotide probes for detection and analysis of other non-coding RNAs, as well as mRNAs, mRNA splice variants, allelic variants of single transcripts, mutations, deletions, or duplications of particular exons in transcripts, e.g. alterations associated with human disease, such as cancer.
The present invention relates to the detection and analysis of target nucleotide sequences in a wide variety of nucleic acid samples and more specifically to the methods employing the design and use of oligonucleotide probes that are useful for detecting and analysing target nucleotide sequences, especially RNA target sequences, such as microRNAs and their target mRNAs and siRNA sequences of interest and for detecting differences between nucleic acid samples (e.g., such as samples from a cancer patient and a healthy patient).
The expanding inventory of international sequence databases and the concomitant sequencing of nearly 200 genomes representing all three domains of life—bacteria, archea and eukaryota—have been the primary drivers in the process of de-constructing living organisms into comprehensive molecular catalogs of genes, transcripts and proteins. The importance of the genetic variation within a single species has become apparent, extending beyond the completion of genetic blueprints of several important genomes, culminating in the publication of the working draft of the hu-man genome sequence in 2001 (Lander, Linton, Birren et al., 2001 Nature 409: 860-921; Venter, Adams, Myers et al., 2001 Science 291: 1304-1351; Sachidanandam, Weissman, Schmidt et al., 2001 Nature 409: 928-933). On the other hand, the increasing number of detailed, large-scale molecular analyses of transcription originating from the human and mouse genomes along with the recent identification of several types of non-protein-coding RNAs, such as small nuclear RNAs, siRNAs, microRNAs and antisense RNAs, indicate that the transcriptomes of higher eukaryotes are much more complex than originally anticipated (Wong et al. 2001, Genome Research 11: 1975-1977; Kampa et al. 2004, Genome Research 14: 331-342).
As a result of the Central Dogma: ‘DNA makes RNA, and RNA makes protein’, RNAs have been considered as simple molecules that just translate the genetic information into protein. Recently, it has been estimated that although most of the genome is transcribed, almost 97% of the genome does not encode proteins in higher eukaryotes, but putative, non-coding RNAs (Wong et al. 2001, Genome Research 11: 1975-1977). The non-coding RNAs (ncRNAs) appear to be particularly well suited for regulatory roles that require highly specific nucleic acid recognition. Therefore, the view of RNA is rapidly changing from the merely informational molecule to comprise a wide variety of structural, informational and catalytic molecules in the cell.
Recently, a large number of small non-coding RNA genes have been identified and designated as microRNAs (miRNAs) (for review, see Ke et al. 2003, Curr. Opin. Chem. Biol. 7:516-523). The first miRNAs to be discovered were the lin-4 and let-7 that are heterochronic switching genes essential for the normal temporal control of diverse developmental events (Lee et al. 1993, Cell 75:843-854; Reinhart et al. 2000, Nature 403: 901-906) in the roundworm C. elegans. miRNAs have been evolutionarily conserved over a wide range of species and exhibit diversity in expression profiles, suggesting that they occupy a wide variety of regulatory functions and exert significant effects on cell growth and development (Ke et al. 2003, Curr. Opin. Chem. Biol. 7:516-523). Recent work has shown that miRNAs can regulate gene expression at many levels, representing a novel gene regulatory mechanism and supporting the idea that RNA is capable of performing similar regulatory roles as proteins. Understanding this RNA-based regulation will help us to understand the complexity of the genome in higher eukaryotes as well as understand the complex gene regulatory networks.
miRNAs are 19-25 nucleotide (nt) RNAs that are processed from longer endogenous hairpin transcripts (Ambros et al. 2003, RNA 9: 277-279). To date more than 1345 microRNAs have been identified in humans, worms, fruit flies and plants according to the miRNA registry database release 5.0 in September 2004, hosted by Sanger Institute, UK, and many miRNAs that correspond to putative genes have also been identified. Some miRNAs have multiple loci in the genome (Reinhart et al. 2002, Genes Dev. 16: 1616-1626) and occasionally, several miRNA genes are arranged in tandem clusters (Lagos-Quintana et al. 2001, Science 294: 853-858). The fact that many of the miRNAs reported to date have been isolated just once suggests that many new miRNAs will be discovered in the future. A recent in-depth transcriptional analysis of the human chromosomes 21 and 22 found that 49% of the observed transcription was outside of any known annotation, and furthermore, that these novel transcripts were both coding and non-coding RNAs (Kampa et al. 2004, Genome Research 14: 331-342). The identified miRNAs to date represent most likely the tip of the iceberg, and the number of miRNAs might turn out to be very large.
The combined characteristics of microRNAs characterized to date (Ke et al. 2003, Curr. Opin. Chem. Biol. 7:516-523; Lee et al. 1993, Cell 75:843-854; Reinhart et al. 2000, Nature 403: 901-906) can be summarized as:
Several lines of evidence suggest that the enzymes Dicer and Argonaute are crucial participants in miRNA biosynthesis, maturation and function (Grishok et al. 2001, Cell 106: 23-24). Mutations in genes required for miRNA biosynthesis lead to genetic developmental defects, which are, at least in part, derived from the role of generating miRNAs. The current view is that miRNAs are cleaved by Dicer from the hairpin precursor in the form of duplex, initially with 2 or 3 nt overhangs in the 3′ ends, and are termed pre-miRNAs. Cofactors join the pre-miRNP and unwind the pre-miRNAs into single-stranded miRNAs, and pre-miRNP is then transformed to miRNP. miRNAs can recognize regulatory targets while part of the miRNP complex. There are several similarities between miRNP and the RNA-induced silencing complex, RISC, including similar sizes and both containing RNA helicase and the PPD proteins. It has therefore been proposed that miRNP and RISC are the same RNP with multiple functions (Ke et al. 2003, Curr. Opin. Chem. Biol. 7:516-523). Different effectors direct miRNAs into diverse pathways. The structure of pre-miRNAs is consistent with the observation that 22 nt RNA duplexes with 2 or 3 nt overhangs at the 3′ ends are beneficial for reconstitution of the protein complex and might be required for high affinity binding of the short RNA duplex to the protein components (for review, see Ke et al. 2003, Curr. Opin. Chem. Biol. 7:516-523).
Growing evidence suggests that miRNAs play crucial roles in eukaryotic gene regulation. The first miRNAs genes to be discovered, lin-4 and let-7, base-pair incompletely to repeated elements in the 3′ untranslated regions (UTRs) of other heterochronic genes, and regulate the translation directly and negatively by antisense RNA-RNA interaction (Lee et al. 1993, Cell 75:843-854; Reinhart et al. 2000, Nature 403: 901-906). Other miRNAs are thought to interact with target mRNAs by limited complementary and suppressed translation as well (Lagos-Quintana et al. 2001, Science 294: 853-858; Lee and Ambros 2001, Science 294: 858-862). Many studies have shown, however, that given a perfect complementarity between miRNAs and their target RNA, could lead to target RNA degradation rather than inhibit translation (Hutvagner and Zamore 2002, Science 297: 2056-2060), suggesting that the degree of complementarity determines their functions. By identifying sequences with near complementarity, several targets have been predicted, most of which appear to be potential transcriptional factors that are crucial in cell growth and development. The high percentage of predicted miRNA targets acting as developmental regulators and the conservation of target sites suggest that miRNAs are involved in a wide range of organism development and behaviour and cell fate decisions (for review, see Ke et al. 2003, Curr. Opin. Chem. Biol. 7:516-523). For example, John et al. 2004 (PLOS Biology 2: e363) used known mammalian miRNAs to scan the 3′ untranslated regions (UTRs) from human, mouse and rat genomes for potential miRNA target sites using a scanning algorithm based on sequence complementarity between the mature miRNA and the target site, binding energy of the miRNA:mRNA duplex and evolutionary conservation. They identified a total of 2307 target mRNAs conserved across the mammals with more than one target site at 90% conservation of target site sequence and 660 target genes at 100% conservation level. Scanning of the two fish genomes; Danio rerio (zebrafish) and Fugu rubripes (Fugu) identified 1000 target genes with two or more conserved miRNA sites between the two fish species (John et al. 2004 PLoS Biology 2: e363). Among the predicted targets, particularly interesting groups included mRNA encoding transcription factors, components of the miRNA machinery, other proteins involved in the translational regulation as well as components of the ubiquitin machinery. Wang et al. 2004 (Genome Biology 5:R65) have developed and applied a computational algorithm to predict 95 Arabidopsis thaliana miRNAs, which included 12 known ones and 83 new miRNAs. The 83 new miRNAs were found to be conserved with more than 90% sequence identity between the Arabidopsis and rice genomes. Using the Smith-Waterman nucleotide-alignment algorithm to predict mRNA targets for the 83 new miRNAs and by focusing on target sites that were conserved in both Arabidopsis and rice, Wang et al. 2004 (Genome Biology 5:R65) predicted 371 mRNA targets with an average of 4.8 targets per miRNA. A large proportion of these mRNA targets encoded proteins with transcription regulatory activity.
Analysis of the genomic location of miRNAs indicates that they play important roles in human development and disease. Several human diseases have already been pinpointed in which miRNAs or their processing machinery might be implicated. One of them is spinal muscular atrophy (SMA), a paediatric neurodegenerative disease caused by reduced protein levels or loss-of-function mutations of the survival of motor neurons (SMN) gene (Paushkin et al. 2002, Curr. Opin. Cell Biol. 14: 305-312). Two proteins (Gemin3 and Gemin4) that are part of the SMN complex are also components of miRNPs, whereas it remains to be seen whether miRNA biogenesis or function is dysregulated in SMA and what effect this has on pathogenesis. Another neurological disease linked to mi/siRNAs is fragile X mental retardation (FXMR) caused by absence or mutations of the fragile X mental retardation protein (FMRP) (Nelson et al. 2003, TIBS 28: 534-540), and there are additional clues that miRNAs might play a role in other neurological diseases. Yet another interesting finding is that the miR-224 gene locus lies within the minimal candidate region of two different neurological diseases: early-onset Parkinsonism and X-linked mental retardation (Dostie et al. 2003, RNA: 9: 180-186). Links between cancer and miRNAs have also been recently described. The most frequent single genetic abnormality in chronic lymphocytic leukaemia (CLL) is a deletion localized to chromosome 13q14 (50% of the cases). A recent study determined that two different miRNA (miR15 and miR16) genes are clustered and located within the intron of LEU2, which lies within the deleted minimal region of the B-cell chronic lymphocytic leukaemia (B-CLL) tumour suppressor locus, and both genes are deleted or down-regulated in the majority of CLL cases (Calin et al. 2002, Proc. Natl. Acad. Sci. U.S.A. 99: 15524-15529). It has been anticipated that connections between miRNAs and human diseases will only strengthen in parallel with the knowledge of miRNAs and the gene networks that they control. Moreover, the understanding of the regulation of RNA-mediated gene expression is leading to the development of novel therapeutic approaches that will be likely to revolutionize the practice of medicine (Nelson et al. 2003, TIBS 28: 534-540).
Some of the recent attention paid to small RNAs in the size range of 21 to 25 nt is due to the phenomenon RNA interference (RNAi), in which double-stranded RNA leads to the degradation of any RNA that is homologous (Fire et al. 1998, Nature 391: 806-811). RNAi relies on a complex and ancient cellular mechanism that has probably evolved for protection against viral attack and mobile genetic elements. A crucial step in the RNAi mechanism is the generation of short interfering RNAs (siRNAs), double-stranded RNAs that are about 22 nt long each. The siRNAs lead to the degradation of homologous target RNA and the production of more siRNAs against the same target RNA (Lipardi et al. 2001, Cell 107: 297-307). The present view for the mRNA degradation pathway of RNAi is that antiparallel Dicer dimers cleave long double-stranded dsRNAs to form siRNAs in an ATP-dependent manner. The siRNAs are then incorporated in the RNA-induced silencing complex (RISC) and ATP-dependent unwinding of the siRNAs activates RISC (Zhang et al. 2002, EMBO J. 21: 5875-5885; Nykanen et al. 2001, Cell 107: 309-321). The active RISC complex is thus guided to degrade the specific target mRNAs.
Detection and Analysis of microRNAs and siRNAs
The current view that miRNAs may represent a newly discovered, hidden layer of gene regulation has resulted in high interest among researchers around the world in the discovery of miRNAs, their targets and mechanism of action. Detection and analysis of these small RNAs is, however not trivial. Thus, the discovery of more than 1400 miRNAs to date has required taking advantage of their special features. First, the research groups have used the small size of the miRNAs as a primary criterion for isolation and detection. Consequently, standard cDNA libraries would lack miRNAs, primarily because RNAs that small are normally excluded by sixe selection in the cDNA library construction procedure. Total RNA from fly embryos, worms or HeLa cells have been size fractionated so that only molecules 25 nucleotides or smaller would be captured (Moss 2002, Curr. Biology 12: R138-R140). Synthetic oligomers have then been ligated directly to the RNA pools using T4 RNA ligase. Then the sequences have been reverse-transcribed, amplified by PCR, cloned and sequenced (Moss 2002, Curr. Biology 12: R138-R140). The genome databases have subsequently been queried with the sequences, confirming the origin of the miRNAs from these organisms as well as placing the miRNA genes physically in the context of other genes in the genome. The vast majority of the cloned sequences have been located in intronic regions or between genes, occasionally in clusters, suggesting that the tandemly arranged miRNAs are processed from a single transcript to allow coordinate regulation. Furthermore, the genomic sequences have revealed the fold-back structures of the miRNA precursors (Moss 2002, Curr. Biology 12: R138-R140).
The size and often low level of expression of different miRNAs require the use of sensitive and quantitative analysis tools. Due to their small size of 19-25 nt, the use of quantitative real-time PCR for monitoring expression of mature miRNAs is excluded. Therefore, most miRNA researchers currently use Northern blot analysis combined with polyacrylamide gels to examine expression of both the mature and pre-miRNAs (Reinhart et al. 2000, Nature 403: 901-906; Lagos-Quintana et al. 2001, Science 294: 853-858; Lee and Ambros 2001, Science 294: 862-864). Primer extension has also been used to detect the mature miRNA (Zeng and Cullen 2003, RNA 9: 112-123). The disadvantage of all the gel-based assays (Northern blotting, primer extension, RNase protection assays etc.) as tools for monitoring miRNA expression includes low throughput and poor sensitivity. Consequently, a large amount of total RNA per sample is required for Northern analysis of miRNAs, which is not feasible when the cell or tissue source is limited.
DNA microarrays would appear to be a good alternative to Northern blot analysis to quantify miRNAs in a genome-wide scale, since microarrays have excellent throughput. Krichevsky et al. 2003 used cDNA microarrays to monitor the expression of miRNAs during neuronal development with 5 to 10 μg aliquot of input total RNA as target, but the mature miRNAs had to be separated from the miRNA pre-cursors using micro concentrators prior to microarray hybridizations (Krichevsky et al. 2003, RNA 9: 1274-1281). Liu et al 2004 (Liu et al. 2004, Proc. Natl. Acad. Sci, U.S.A 101:9740-9744) have developed a microarray for expression profiling of 245 human and mouse miRNAs using 40-mer DNA oligonucleotide capture probes. Thomson et al. 2004 (Thomson et al. 2004, Nature Methods 1:1-6) describe the development of a custom oligonucleotide microarray platform for expression profiling of 124 mammalian miRNAs conserved in human and mouse using oligonucleotide capture probes complementary to the mature microRNAs. The microarray was used in expression profiling of the 124 miRNAs in question in different adult mouse tissues and embryonic stages. A similar approach was used by Miska et al. 2004 (Genome Biology 2004; 5:R68) for the development of an oligoarray for expression profiling of 138 mammalian miRNAs, including 68 miRNAs from rat and monkey brains. Yet another approach was taken by Barad et al. 2004 (Genome Research 2004; 14: 2486-2494), who developed a 60-mer oligonucleotide microarray platform for known human mature miRNAs and their precursors. The drawback of all DNA-based oligonucleotide arrays regardless of the capture probe length is the requirement of high concentrations of labelled input target RNA for efficient hybridization and signal generation, low sensitivity for rare and low-abundant miRNAs, and the necessity for post-array validation using more sensitive assays such as real-time quantitative PCR, which is not currently feasible. In addition, at least in some array platforms discrimination of highly homologous miRNA differing by just one or two nucleotides could not be achieved, thus presenting problems in data interpretation, although the 60-mer microarray by Barad et al. 2004 (Genome Research 2004; 14: 2486-2494) appears to have adequate specificity.
A PCR approach has also been used to determine the expression levels of mature miRNAs (Grad et al. 2003, Mol. Cell. 11: 1253-1263). This method is useful to clone miRNAs, but highly impractical for routine miRNA expression profiling, since it involves gel isolation of small RNAs and ligation to linker oligonucleotides. Allawi et al. (2004, RNA 10: 1153-1161) have developed a method for quantitation of mature miRNAs using a modified Invader assay. Although apparently sensitive and specific for the mature miRNA, the drawback of the Invader quantitation assay is the number of oligonucleotide probes and individual reaction steps needed for the complete assay, which increases the risk of cross-contamination between different assays and samples, especially when high-throughput analyses are desired. Schmittgen et al. (2004, Nucleic Acids Res. 32: e43) describe an alternative method to Northern blot analysis, in which they use real-time PCR assays to quantify the expression of miRNA precursors. The disadvantage of this method is that it only allows quantification of the precursor miRNAs, which does not necessarily reflect the expression levels of mature miRNAs. In order to fully characterize the expression of large numbers of miRNAs, it is necessary to quantify the mature miRNAs, such as those expressed in human disease, where alterations in miRNA biogenesis produce levels of mature miRNAs that are very different from those of the precursor miRNA. For example, the precursors of 26 miRNAs were equally expressed in non-cancerous and cancerous colorectal tissues from patients, whereas the expression of mature human miR143 and miR145 was greatly reduced in cancer tissues compared with non-cancer tissues, suggesting altered processing for specific miRNAs in human disease (Michael et al. 2003, Mol. Cancer. Res. 1: 882-891). On the other hand, recent findings in maize with miR166 and miR165 in Arabidopsis thaliana, indicate that microRNAs act as signals to specify leaf polarity in plants and may even form movable signals that emanate from a signalling centre below the incipient leaf (Juarez et al. 2004, Nature 428: 84-88; Kidner and Martienssen 2004, Nature 428: 81-84).
Most of the miRNA expression studies in animals and plants have utilized Northern blot analysis, tissue-specific small RNA cloning and expression profiling by microarrays or real-time PCR of the miRNA hairpin precursors, as described above. However, these techniques lack the resolution for addressing the spatial and temporal expression patterns of mature miRNAs. Due to the small size of mature miRNAs, detection of them by standard RNA in situ hybridization has proven difficult to adapt in both plants and vertebrates, even though in situ hybridization has recently been reported in A. thaliana and maize using RNA probes corresponding to the stem-loop precursor miRNAs (Chen et al. 2004, Science 203: 2022-2025; Juarez et al. 2004, Nature 428: 84-88). Brennecke et al. 2003 (Cell 113: 25-36) and Mansfield et al. 2004 (Nature Genetics 36: 1079-83) report on an alternative method in which reporter transgenes, so-called sensors, are designed and generated to detect the presence of a given miRNA in an embryo. Each sensor contains a constitutively expressed reporter gene (e.g. lacZ or green fluorescent protein) harbouring miRNA target sites in its 3′-UTR. Thus, in cells that lack the miRNA in question, the transgene RNA is stable allowing detection of the reporter, whereas cells expressing the miRNA, the sensor mRNA is targeted for degradation by the RNAi pathway. Although sensitive, this approach is time-consuming since it requires generation of the expression constructs and transgenes. Furthermore, the sensor-based technique detects the spatiotemporal miRNA expression patterns via an indirect method as opposed to direct in situ hybridization of the mature miRNAs.
The large number of miRNAs along with their small size makes it difficult to create loss-of-function mutants for functional genomics analyses. Another potential problem is that many miRNA genes are present in several copies per genome occurring in different loci, which makes it even more difficult to obtain mutant phenotypes. Boutla et al. 2003 (Nucleic Acids Research 31: 4973-4980) describe the use of DNA antisense oligonucleotides complementary to 11 different miRNAs in Drosophila as well as their use to inactivate the miRNAs by injecting the DNA oligonucleotides into fly emryos. Of the 11 DNA antisense oligonucleotides, only 4 constructs showed severe interference with normal development, while the remaining 7 oligonucleotides didn't show any phenotypes presumably due to their inability to inhibit the miRNA in question. Thus, the success rate for using DNA antisense oligonucleotides to inhibit miRNA function would most likely be too low to allow functional analyses of miRNAs on a larger, genomic scale. An alternative approach to this has been reported by Hutvagner et al. 2004 (PLoS Biology 2: 1-11), in which 2′-O-methyl antisense oligonucleotides could be used as potent and irreversible inhibitors of siRNA and miRNA function in vitro and in vivo in Drosophila and C. elegans, thereby inducing a loss-of-function phenotype. A drawback of this method is the need of high 2′-O-methyl oligonucleotide concentrations (100 micromolar) in transfection and injection experiments, which may be toxic to the animal.
In conclusion, the biggest challenge in detection, quantitation and functional analysis of the mature miRNAs as well as siRNAs using currently available methods is their small size of the of 19-25 nt and often low level of expression
RNA editing is used to describe any specific change in the primary sequence of an RNA molecule, excluding other mechanistically defined processes such as alternative splicing or polyadenylation. RNA alterations due to editing fall into two broad categories, depending on whether the change happens at the base or nucleotide level (Gott 2003, C. R. Biologies 326 901-908). RNA editing is quite widespread, occurring in mammals, viruses, marsupials, plants, flies, frogs, worms, squid, fungi, slime molds, dinoflagellates, kinetoplastid protozoa, and other unicellular eukaryotes. The current list most likely represents only the tip of the iceberg; based on the distribution of homologues of known editing enzymes, as RNA editing almost certainly occurs in many other species, including all metazoa. Since RNA editing can be regulated in a developmental or tissue-specific manner, it is likely to play a significant role in the etiology of human disease (Gott 2003, C. R. Biologies 326 901-908).
A common feature for eukaryotic genes is that they are composed of protein-encoding exons and introns. Introns are characterized by being excised from the pre-mRNA molecule in RNA splicing, as the sequences on each side of the intron are spliced together. RNA splicing not only provides functional mRNA, but is also responsible for generating additional diversity. This phenomenon is called alternative splicing, which results in the production of different mRNAs from the same gene. The mRNAs that represent isoforms arising from a single gene can differ by the use of alternative exons or retention of an intron that disrupts two exons. This process often leads to different protein products that may have related or drastically different, even antagonistic, cellular functions. There is increasing evidence indicating that alternative splicing is very widespread (Croft et al. Nature Genetics, 2000). Recent studies have revealed that at least 80% of the roughly 35,000 genes in the human genome are alternatively spliced (Kampa et al. 2004, Genome Research 14: 331-342). Clearly, by combining different types of modifications and thus generating different possible combinations of transcripts of different genes, alternative splicing together with RNA editing are potent mechanisms for generating protein diversity. Analysis of the alternative splice variants and RNA editing, in turn, represents a novel approach to functional genomics, disease diagnostics and pharmacogenomics.
The detection of the detailed structure of the transcriptional output is an important goal for molecular characterization of a cell or tissue. Without the ability to detect and quantify the splice variants present in one tissue, the transcript content or the protein content cannot be described accurately. Molecular medical research shows that many cancers result in altered levels of splice variants, so an accurate method to detect and quantify these transcripts is required. Mutations that produce an aberrant splice form can also be the primary cause of such severe diseases such as spinal muscular dystrophy and cystic fibrosis.
Much of the study of human disease, indeed much of genetics is based upon the study of a few model organisms. The evolutionary stability of alternative splicing patterns and the degree to which splicing changes according to mutations and environmental and cellular conditions influence the relevance of these model systems. At present, there is little understanding of the rates at which alternative splicing patterns or RNA editing change, and the factors influencing these rates.
Previously, other analysis methods have been performed with the aim of detecting either splicing of RNA transcripts per se in yeast, or of detecting putative exon skipping splicing events in rat tissues, but neither of these approaches had sufficient resolution to estimate quantities of splice variants, a factor that could be essential to an understanding of the changes in cell life cycle and disease. Thus, improved methods are needed for nucleic acid hybridization and quantitation.
RNA-mediated gene regulation is widespread in higher eukaryotes and complex genetic phenomena like RNA interference, co-suppression, transgene silencing, imprinting, methylation, and possibly position-effect variegation and transvection, all involve intersecting pathways based on or connected to RNA signalling (Mattick 2001; EMBO reports 2, 11: 986-991). Recent studies indicate that antisense transcription is a very common phenomenon in the mouse and human genomes (Okazaki et al. 2002; Nature 420: 563-573; Yelin et al. 2003, Nature Biotechnol.). Thus, antisense modulation of gene expression in eukaryotic cells, e.g. human cells appear to be a common regulatory mechanism.
The challenges of establishing genome function and understanding the layers of information hidden in the complex transcriptomes of higher eukaryotes call for novel, improved technologies for detection and analysis of non-coding RNA and protein-coding RNA molecules in complex nucleic acid samples. Thus, it would be highly desirable to be able to detect and analyse the expression of mature microRNAs, siRNAs, RNA-edited transcripts as well as highly homologous splice variants in the transcriptomes of eukaryotes using methods based on specific and sensitive oligonucleotide detection probes.
The present invention solves the current problems faced by conventional approaches used in detection and analysis of mature miRNAs, their target mRNAs as well as siRNAs as outlined above by providing a method for the design, synthesis and use of novel oligonucleotide compositions and probe sequences with improved sensitivity and high sequence specificity for RNA target sequences, such as mature miRNAs and siRNAs so that they are unlikely to detect a random RNA target molecule. Such oligonucleotide probes comprise a recognition sequence complementary to the RNA target sequence, which said recognition sequence is substituted with high-affinity nucleotide analogues, e.g. LNA, to increase the sensitivity and specificity of conventional oligonucleotides, such as DNA oligonucleotides, for hybridization to short target sequences, e.g. mature miRNAs, stem-loop precursor miRNAs, siRNAs or other non-coding RNAS as well as miRNA binding sites in their cognate mRNA targets, mRNAs, mRNA splice variants, RNA-edited mRNAs and antisense RNAs.
In one aspect, the invention features a nucleotide probe including a plurality of LNA monomers that hybridizes to a miRNA. Desirably, two of the plurality of LNA monomers are disposed 3 or 4 nucleotides apart, or a combination thereof. In other embodiments, each LNA monomer in a probe is spaced 3 or 4 nucleotides from the closest LNA monomer. When LNA monomers are spaced apart, only naturally-occurring nucleotides may be disposed between the LNA monomers. In another embodiment, two, three, four, or more LNA monomers are disposed adjacent to one another. The adjacent LNA monomers may be disposed at the 3′ or 5′ end or so that one of the LNA monomers hybridizes to the center of the miRNA. In other embodiments, the prove includes none or at most one mismatched base, deletion, or addition. Desirably, the probe hybridizes to the miRNA under stringent conditions. Or high stringency conditions. In certain embodiments, the melting point of the duplex formed between the probe and the miRNA is at least 1° C. higher, e.g., at least 5° C., than the melting point of the duplex formed between the miRNA and a nucleic acid sequence not comprising a LNA monomer or any modified backbone. The probe may include at least 70% DNA; at least 10% LNA units; and/or at most 30% LNA units. In addition, the probe may be at least 8 nucleotides long and at most 30 nucleotides long. The probe may further include a 5′ or 3′ amino group and/or a 5′ or 3′ label, e.g., a fluorescent (such as fluorescein) or radioactive label. Other potential modifications of probes are described herein. In other embodiments, the probe when hydridized to the miRNA provides a substrate for RNase H; alternatively, the probe when hybridized to the miRNA may not provide a substrate for RNase H. Preferably, the probes of the invention exhibit increases binding affinity for the target sequence by at least two-fold compared to probes of the same sequence without the modification, under the same conditions for hybridization or stringent hybridization conditions.
The invention further features a method of creating a nucleotide duplex by providing a miRNA; and contacting the miRNA with a probe of the invention that hybridizes to the miRNA. The invention also features a method of inhibiting the biological activity of a miRNA by providing the miRNA; and contacting the miRNA with a probe of the invention that hybridizes to said miRNA, thereby inhibiting the biological activity of the miRNA. In addition, the invention features a method of determining the biological activity of a miRNA by providing the miRNA; contacting the miRNA with a probe of the invention that hybridizes to the miRNA; and assaying the biological activity. Any method of the invention may involve contacting a probe with miRNA that is endogenously or exogenously produced. Such contacting may occur in vitro or in vivo or within or without a cell, which may or may not naturally express the miRNA.
In another aspect, the invention features a kit including a probe of the invention and packaging and/or labeling indicative of the miRNA to which the probe hybridizes and conditions under which the hybridization occurs.
Exemplary miRNAs are described herein and are known in the art, e.g., in U.S. 2005/0182005; WO 2005/013901, and the miRBase Sequence Database (D140-D144 Nucleic Acids Research, 2006, Vol. 34, Database issue), each of which is hereby incorporated by reference.
The invention also features probes, as described herein, in combination with a pharmaceutically acceptable carrier. Such carriers are known in the art.
Also, discussed primarily with respect to miRNA, LNA containing probes, polynucleotides, and oligonucleotides are broadly applicable to other antisense uses, as described herein.
The present invention provides the design and development of novel oligonucleotide compositions and probe sequences for accurate, highly sensitive and specific detection and functional analysis of miRNAs, their target mRNAs and siRNA transcripts.
The present invention enables discrimination between mRNA splice variants as well as RNA-edited transcripts and detects each variant in a nucleic acid sample, such as a sample derived from a patient in e.g. addressing the spatiotemporal expression patterns by RNA in situ hybridization.
The present invention provides a method for detection and functional analysis of non-coding antisense RNAs, as well as a method for detecting the overlapping regions between sense-antisense transcriptional units.
The invention features a method of designing the detection probe sequences by selecting optimal substitution patterns for the high-affinity analogues, e.g. LNAs for the detection probes. This method involves (a) substituting the detection probe sequence with the high affinity analogue LNA in chimeric LNA-DNA oligonucleotides using regular spacing between the LNA substitutions, e.g. at every second nucleotide position, every third nucleotide position, or every fourth nucleotide position, in order to promote the A-type duplex geometry between the substituted detection probe and its complementary RNA target; with the said LNA monomer substitutions spiked in all the possible phases in the probe sequence with an unsubstituted monomer at the 5′-end position and 3′-end position in all the substituted designs; (b) determining the ability of the designed detection probes with different regular substitution patterns to self-anneal; and (c) determining the melting temperature of the substituted probes sequences of the invention, and (d) selecting the probe sequences with the highest melting temperatures and lowest self-complementarity score, i.e. lowest ability to self-anneal are selected. In another aspect of the invention
In another aspect the invention features a method of designing the detection probe sequences by selecting optimal substitution patterns for the LNAs, which said method involves substituting the detection probe sequence with the high affinity analogue LNA in chimeric LNA-DNA oligonucleotides using irregular spacing between the LNA monomers and selecting the probe sequences with the highest melting temperatures and lowest self-complementarity score. In yet another aspect the invention features a computer code for a preferred software program of the invention for the design and selection of the said substituted detection probe sequences.
In another aspect the invention features detection probe sequences containing a ligand. Such ligand-containing detection probes of the invention are useful for isolating target RNA molecules from complex nucleoc acid mixtures, such as miRNAs, their cognate target mRNAs and siRNAs. Ligands comprise biotin and functional groups such as: aromatic groups (such as benzene, pyridine, naphthalene, anthracene, and phenanthrene), heteroaromatic groups (such as thiophene, furan, tetrahydrofuran, pyridine, dioxane, and pyrimidine), carboxylic acids, carboxylic acid esters, carboxylic acid halides, carboxylic acid azides, carboxylic acid hydrazides, sulfonic acids, sulfonic acid esters, sulfonic acid halides, semicarbazides, thiosemicar-bazides, aldehydes, ketones, primary alcohols, secondary alcohols, tertiary alcohols, phenols, alkyl halides, thiols, disulphides, primary amines, secondary amines, tertiary amines, hydrazines, epoxides, maleimides, C1-C20 alkyl groups optionally interrupted or terminated with one or more heteroatoms such as oxygen atoms, nitrogen atoms, and/or sulphur atoms, optionally containing aromatic or mono/polyunsaturated hydrocarbons, polyoxyethylene such as polyethylene glycol, oligo/polyamides such as poly-α-alanine, polyglycine, polylysine, peptides, oligo/polysaccharides, oligo/polyphosphates, toxins, antibiotics, cell poisons, and steroids, and also affinity ligands, i.e. functional groups or biomolecules that have a specific affinity for sites on particular proteins, antibodies, poly- and oligosaccharides, and other biomolecules.
In another aspect the invention features detection probe sequences, which sequences have been further modified by Selectively Binding Complementary (SBC) nucleobases, i.e. modified nucleobases that can make stable hydrogen bonds to their complementary nucleobases, but are unable to make stable hydrogen bonds to other SBC nucleobases. Such SBC monomer substitutions are especially useful when highly self-complementary detection probe sequences are employed. As an example, the SBC nucleobase A′, can make a stable hydrogen bonded pair with its complementary unmodified nucleobase, T. Likewise, the SBC nucleobase T′ can make a stable hydrogen bonded pair with its complementary unmodified nucleobase, A. However, the SBC nucleobases A′ and T′ will form an unstable hydrogen bonded pair as compared to the base pairs A′-T and A-T′. Likewise, a SBC nucleobase of C is designated C′ and can make a stable hydrogen bonded pair with its complementary unmodified nucleobase G, and a SBC nucleobase of G is designated G′ and can make a stable hydrogen bonded pair with its complementary unmodified nucleobase C, yet C′ and G′ will form an unstable hydrogen bonded pair as compared to the base pairs C′-G and C-G′. A stable hydrogen bonded pair is obtained when 2 or more hydrogen bonds are formed e.g. the pair between A′ and T, A and T′, C and G′, and C′ and G. An unstable hydrogen bonded pair is obtained when 1 or no hydrogen bonds is formed e.g. the pair between A′ and T′, and C′ and G′. Especially interesting SBC nucleobases are 2,6-diaminopurine (A′, also called D) together with 2-thio-uracil (U′, also called 2SU) (2-thio-4-oxo-pyrimidine) and 2-thio-thymine (T′, also called 2ST) (2-thio-4-oxo-5-methyl-pyrimidine).
In another aspect the detection probe sequences of the invention are covalently bonded to a solid support by reaction of a nucleoside phosphoramidite with an activated solid support, and subsequent reaction of a nucleoside phosphoramide with an activated nucleotide or nucleic acid bound to the solid support. In some embodiments, the solid support or the detection probe sequences bound to the solid support are activated by illumination, a photogenerated acid, or electric current. In other embodiments the detection probe sequences contain a spacer, e.g. a randomized nucleotide sequence or a non-base sequence, such as hexaethylene glycol, between the reactive group and the recognition sequence. Such covalently bonded detection probe sequence populations are highly useful for large-scale detection and expression profiling of mature miRNAs, stem-loop precursor miRNAs, siRNAs and other non-coding RNAs.
The present oligonucleotide compositions and detection probe sequences of invention are highly useful and applicable for detection of individual small RNA molecules in complex mixtures composed of hundreds of thousands of different nucleic acids, such as detecting mature miRNAs, their target mRNAs or siRNAs, by Northern blot analysis or for addressing the spatiotemporal expression patterns of miRNAs, siRNAs or other non-coding RNAs as well as mRNAs by in situ hybridization in whole-mount embryos, whole-mount animals or plants or tissue sections of plants or animals, such as human, mouse, rat, zebrafish, Caenorhabditis elegans, Drosophila melanogaster, Arabidopsis thaliana, rice and maize. The present oligonucleotide compositions and detection probe sequences of the invention are furthermore highly useful and applicable for large-scale and genome-wide expression profiling of mature miRNAs, siRNAs or other non-coding RNAs in animals and plants by oligonucleotide microarrays. The present oligonucleotide compositions and detection probe sequences are furthermore highly useful in functional analysis of miRNAs, siRNAs or other non-coding RNAs in vitro and in vivo in plants or animals, such as human, mouse, rat, zebrafish, Caenorhabditis elegans, Drosophila melanogaster, Arabidopsis thaliana, rice and maize, by inhibiting their mode of action, e.g. the binding of mature miRNAs to their cognate target mRNAs. The oligonucleotide compositions and detection probe sequences of invention are also applicable to detecting, testing, diagnosing or quantifying miRNAs, siRNAs, other non-coding RNAs, RNA-edited transcripts or alternative mRNA splice variants implicated in or connected to human disease in complex human nucleic acid samples, e.g. from cancer patients.
Other features and advantages of the invention will be apparent from the following description, the figures, and the claims.
a: anti-miR-181a LNA inhibits miR-181a and miR-181b. C2C12 cells were transfected with control (c) or anti-miR-181 (181) LNA and analyzed by Northern blot as described in
b: Synthetic miRNAs transfected into C2C12 cells. Proliferating C2C12 cells were transfected with the double-stranded synthetic oligonucleotides (50 nM) shown in the upper panel (mismatches are in bold; miR-181a-1: a fully annealed doubled-stranded sequence: miR-181a-2: a double-stranded sequence destabilized to favour incorporation of the miRNA strand into protein complexes: miR181a-3, a double stranded sequence mimicking the predicted product of precursor processing by DICER). Northern blot analysis of transfected cells showed that the last design was the most efficient with regard to the level of intracellular miRNA (lower panel; 1, 2, 3: miR-181a-1, miR-181a-2 and miR-181a-3), and was used in subsequent experiments.
c: p21 is down-regulated in miR-181-depleted cells. C2C12 cells were transfected with the control (c) or wt LNAs as in
a: HoxA11 mRNA is not affected by anti-miR-181 LNA: C2C12 cells were transfected with 50 nM of LNA, either control (con) or anti-miR-181 (miR-181) or mock transfected (−), placed in differentiation medium for 2 days (dif) or kept in proliferation medium (prol), and analyzed by real time RT-PCR for HoxA11 and 36B4 mRNA. Shown are the ratios between HoxA11 and 36B4.
b: MiR181 a and b do not synergize for HoxA11 target inhibition: HeLa cells were transfected as in
c: Several mIRNAs predicted to bind to HoxA11 mRNA are upregulated in differentiating myoblasts. RNA from C2C12 cells, either proliferating (P) or after 3 days of differentiation (D), were analyzed by Northern blot as described in
d: Down-regulation of HoxA11 or ectopic expression of miR-181 do not induce differentiation of proliferating C2C12 cells. C2CC12 cells were transfected with a control siRNA (c) an siRNA against Hox-A11 (Hox) or synthetic double-stranded miR181a (181) as in
In the present context “ligand” means something that binds. Ligands comprise biotin and functional groups such as: aromatic groups (such as benzene, pyridine, naphthalene, anthracene, and phenanthrene), heteroaromatic groups (such as thiophene, furan, tetrahydrofuran, pyridine, dioxane, and pyrimidine), carboxylic acids, carboxylic acid esters, carboxylic acid halides, carboxylic acid azides, carboxylic acid hydrazides, sulfonic acids, sulfonic acid esters, sulfonic acid halides, semicarbazides, thiosemicarbazides, aldehydes, ketones, primary alcohols, secondary alcohols, tertiary alcohols, phenols, alkyl halides, thiols, disulphides, primary amines, secondary amines, tertiary amines, hydrazines, epoxides, maleimides, C1-C20 alkyl groups optionally interrupted or terminated with one or more heteroatoms such as oxygen atoms, nitrogen atoms, and/or sulphur atoms, optionally containing aromatic or mono/polyunsaturated hydrocarbons, polyoxyethylene such as polyethylene glycol, oligo/polyamides such as poly-β-alanine, polyglycine, polylysine, peptides, oligo/polysaccharides, oligo/polyphosphates, toxins, antibiotics, cell poisons, and steroids, and also “affinity ligands”, i.e. functional groups or biomolecules that have a specific affinity for sites on particular proteins, antibodies, poly- and oligosaccharides, and other biomolecules.
The singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a cell” includes a plurality of cells, including mixtures thereof. The term “a nucleic acid molecule” includes a plurality of nucleic acid molecules.
“Transcriptome” refers to the complete collection of transcriptional units of the genome of any species. In addition to protein-coding mRNAs, it also represents non-coding RNAs, such as small nucleolar RNAs, siRNAs, microRNAs and antisense RNAs, which comprise important structural and regulatory roles in the cell.
“Sample” refers to a sample of cells, or tissue or fluid isolated from an organism or organisms, including but not limited to, for example, skin, plasma, serum, spinal fluid, lymph fluid, synovial fluid, urine, tears, blood cells, organs, tumours, and also to samples of in vitro cell culture constituents (including but not limited to conditioned medium resulting from the growth of cells in cell culture medium, recombinant cells and cell components).
An “organism” refers to a living entity, including but not limited to, for example, human, mouse, rat, Drosophila, C. elegans, yeast, Arabidopsis thaliana, maize, rice, zebra fish, primates, domestic animals, etc.
The terms “detection probes” or “detection probe” or “detection probe sequence” refer to an oligonucleotide, which oligonucleotide comprises a recognition sequence complementary to a RNA target sequence, which said recognition sequence is substituted with high-affinity nucleotide analogues, e.g. LNA, to increase the sensitivity and specificity of conventional oligonucleotides, such as DNA oligonucleotides, for hybridization to short target sequences, e.g. mature miRNAs, stem-loop precursor miRNAs, pri-miRNAs, siRNAs or other non-coding RNAs as well as miRNA binding sites in their cognate mRNA targets, mRNAs, mRNA splice variants, RNA-edited mRNAs and antisense RNAs.
The terms “miRNA” and “microRNA” refer to 19-25 nt, e.g., 21-25, non-coding RNAs derived from endogenous genes. They are processed from longer (ca 75 nt) hairpin-like precursors termed pre-miRNAs. MicroRNAs assemble in complexes termed miRNPs and recognize their targets by antisense complementarity. If the microRNAs match 100% their target, i.e. the complementarity is complete, the target mRNA is cleaved, and the miRNA acts like a siRNA. If the match is incomplete, i.e. the complementarity is partial, then the translation of the target mRNA is blocked.
The terms “Small interfering RNAs” or “siRNAs” refer to 21-25 nt RNAs derived from processing of linear double-stranded RNA. siRNAs assemble in complexes termed RISC(RNA-induced silencing complex) and target homologous RNA sequences for endonucleolytic cleavage. Synthetic siRNAs also recruit RISCs and are capable of cleaving homologous RNA sequences
The term “RNA interference” (RNAi) refers to a phenomenon where double-stranded RNA homologous to a target mRNA leads to degradation of the targeted mRNA. More broadly defined as degradation of target mRNAs by homologous siRNAs.
The term “recognition sequence” refers to a nucleotide sequence that is complementary to a region within the target nucleotide sequence essential for sequence-specific hybridization between the target nucleotide sequence and the recognition sequence.
The term “label” as used herein refers to any atom or molecule which can be used to provide a detectable (preferably quantifiable) signal, and which can be attached to a nucleic acid or protein. Labels may provide signals detectable by fluorescence, radioactivity, colorimetric, X-ray diffraction or absorption, magnetism, enzymatic activity, and the like.
As used herein, the terms “nucleic acid”, “polynucleotide” and “oligonucleotide” refer to primers, probes, oligomer fragments to be detected, oligomer controls and unlabelled blocking oligomers and shall be generic to polydeoxyribonucleotides (containing 2-deoxy-D-ribose), to polyribonucleotides (containing D-ribose), and to any other type of polynucleotide which is an N glycoside of a purine or pyrimidine base, or modified purine or pyrimidine bases. There is no intended distinction in length between the term “nucleic acid”, “polynucleotide” and “oligonucleotide”, and these terms will be used interchangeably. These terms refer only to the primary structure of the molecule. Thus, these terms include double- and single-stranded DNA, as well as double- and single stranded RNA. The oligonucleotide is comprised of a sequence of approximately at least 3 nucleotides, preferably at least about 6 nucleotides, and more preferably at least about 8-30 nucleotides corresponding to a region of the designated target nucleotide sequence. “Corresponding” means identical to or complementary to the designated sequence. The oligonucleotide is not necessarily physically derived from any existing or natural sequence but may be generated in any manner, including chemical synthesis, DNA replication, reverse transcription or a combination thereof.
The terms “oligonucleotide” or “nucleic acid” intend a polynucleotide of genomic DNA or RNA, cDNA, semi synthetic, or synthetic origin which, by virtue of its origin or manipulation: (1) is not associated with all or a portion of the polynucleotide with which it is associated in nature; and/or (2) is linked to a polynucleotide other than that to which it is linked in nature; and (3) is not found in nature. Because mononucleotides are reacted to make oligonucleotides in a manner such that the 5′-phosphate of one mononucleotide pentose ring is attached to the 3′ oxygen of its neighbour in one direction via a phosphodiester linkage, an end of an oligonucleotide is referred to as the “5′ end” if its 5′ phosphate is not linked to the 3′ oxygen of a mononucleotide pentose ring and as the “3′ end” if its 3′ oxygen is not linked to a 5′ phosphate of a subsequent mononucleotide pentose ring. As used herein, a nucleic acid sequence, even if internal to a larger oligonucleotide, also may be said to have a 5′ and 3′ ends. When two different, non-overlapping oligonucleotides anneal to different regions of the same linear complementary nucleic acid sequence, the 3′ end of one oligonucleotide points toward the 5′ end of the other; the former may be called the “upstream” oligonucleotide and the latter the “downstream” oligonucleotide.
By the term “SBC nucleobases” is meant “Selective Binding Complementary” nucleobases, i.e. modified nucleobases that can make stable hydrogen bonds to their complementary nucleobases, but are unable to make stable hydrogen bonds to other SBC nucleobases. As an example, the SBC nucleobase A′, can make a stable hydrogen bonded pair with its complementary unmodified nucleobase, T. Likewise, the SBC nucleobase T′ can make a stable hydrogen bonded pair with its complementary unmodified nucleobase, A. However, the SBC nucleobases A′ and T′ will form an unstable hydrogen bonded pair as compared to the base pairs A′-T and A-T′. Likewise, a SBC nucleobase of C is designated C′ and can make a stable hydrogen bonded pair with its complementary unmodified nucleobase G, and a SBC nucleobase of G is designated G′ and can make a stable hydrogen bonded pair with its complementary unmodified nucleobase C, yet C′ and G′ will form an unstable hydrogen bonded pair as compared to the base pairs C′-G and C-G′. A stable hydrogen bonded pair is obtained when 2 or more hydrogen bonds are formed e.g. the pair between A′ and T, A and T′, C and G′, and C′ and G. An unstable hydrogen bonded pair is obtained when 1 or no hydrogen bonds is formed e.g. the pair between A′ and T′, and C′ and G′. Especially interesting SBC nucleobases are 2,6-diaminopurine (A′, also called D) together with 2-thio-uracil (U′, also called 2SU) (2-thio-4-oxo-pyrimidine) and 2-thio-thymine (T′, also called 2ST) (2-thio-4-oxo-5-methyl-pyrimidine).
“SBC LNA oligomer” refers to a “LNA oligomer” containing at least one LNA monomer where the nucleobase is a “SBC nucleobase”. By “LNA monomer with an SBC nucleobase” is meant a “SBC LNA monomer”. Generally speaking SBC LNA oligomers include oligomers that besides the SBC LNA monomer(s) contain other modified or naturally occurring nucleotides or nucleosides. By “SBC monomer” is meant a non-LNA monomer with a SBC nucleobase. By “isosequential oligonucleotide” is meant an oligonucleotide with the same sequence in a Watson-Crick sense as the corresponding modified oligonucleotide e.g. the sequences agTtcATg is equal to agTscD2SUg where s is equal to the SBC DNA monomer 2-thio-t or 2-thio-u, D is equal to the SBC LNA monomer LNA-D and 2SU is equal to the SBC LNA monomer LNA 2SU.
The complement of a nucleic acid sequence as used herein refers to an oligonucleotide which, when aligned with the nucleic acid sequence such that the 5′ end of one sequence is paired with the 3′ end of the other, is in “antiparallel association.” Bases not commonly found in natural nucleic acids that may be included in the nucleic acids of the present invention include, for example, inosine and 7-deazaguanine. Complementarity may not be perfect; stable duplexes may contain mismatched base pairs or unmatched bases. Those skilled in the art of nucleic acid technology can determine duplex stability empirically considering a number of variables including, for example, the length of the oligonucleotide, percent concentration of cytosine and guanine bases in the oligonucleotide, ionic strength, and incidence of mismatched base pairs.
Stability of a nucleic acid duplex is measured by the melting temperature, or “Tm”. The Tm of a particular nucleic acid duplex under specified conditions is the temperature at which half of the duplexes have disassociated.
The term “nucleobase” covers the naturally occurring nucleobases adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U) as well as non-naturally occurring nucleobases such as xanthine, diaminopurine, 8-oxo-N6-methyladenine, 7-deazaxanthine, 7-deazaguanine, N4,N4-ethanocytosin, N6,N6-ethano-2,6-diaminopurine, 5-methylcytosine, 5-(C3-C6)-alkynyl-cytosine, 5-fluorouracil, 5-bromouracil, pseudoisocytosine, 2-hydroxy-5-methyl-4-triazolopyridin, isocytosine, isoguanine, inosine and the “non-naturally occurring” nucleobases described in Benner et al., U.S. Pat. No. 5,432,272 and Susan M. Freier and Karl-Heinz Altmann, Nucleic Acid Research, 25: 4429-4443, 1997. The term “nucleobase” thus includes not only the known purine and pyrimidine heterocycles, but also heterocyclic analogues and tautomers thereof. Further naturally and non naturally occurring nucleobases include those disclosed in U.S. Pat. No. 3,687,808; in chapter 15 by Sanghvi, in Antisense Research and Application, Ed. S. T. Crooke and B. Lebleu, CRC Press, 1993; in Englisch, et al., Angewandte Chemie, International Edition, 30: 613-722, 1991 (see, especially pages 622 and 623, and in the Concise Encyclopedia of Polymer Science and Engineering, J. I. Kroschwitz Ed., John Wiley & Sons, pages 858-859, 1990, Cook, Anti-Cancer Drug Design 6: 585-607, 1991, each of which are hereby incorporated by reference in their entirety).
The term “nucleosidic base” or “nucleobase analogue” is further intended to include heterocyclic compounds that can serve as like nucleosidic bases including certain “universal bases” that are not nucleosidic bases in the most classical sense but serve as nucleosidic bases. Especially mentioned as a universal base is 3-nitropyrrole or a 5-nitroindole. Other preferred compounds include pyrene and pyridyloxazole derivatives, pyrenyl, pyrenylmethylglycerol derivatives and the like. Other preferred universal bases include, pyrrole, diazole or triazole derivatives, including those universal bases known in the art.
By “oligonucleotide,” “oligomer,” or “oligo” is meant a successive chain of monomers (e.g., glycosides of heterocyclic bases) connected via internucleoside linkages. The linkage between two successive monomers in the oligo consist of 2 to 4, desirably 3, groups/atoms selected from —CH2—, —O—, —S—, —NRH, >C═O, >C═NRH, >C═S, —Si(R″)2—, —SO—, —S(O)2—, —P(O)2—, —PO(BH3)—, —P(O,S)—, —P(S)2—, —PO(R″)—, —PO(OCH3)—, and —PO(NHRH)—, where RH is selected from hydrogen and C1-4-alkyl, and R″ is selected from C1-6-alkyl and phenyl. Illustrative examples of such linkages are —CH2—CH2—CH2—, —CH2—CO—CH2—, —CH2—CHOH—CH2—, —O—CH2—O—, —O—CH2—CH2—, —O—CH2—CH═ (including R5 when used as a linkage to a succeeding monomer), —CH2—CH2—O—, —NRH—CH2—CH2—, —CH2—CH2—NRH, —CH2—NRH—CH2—, —CH2—CH2—NRH—, —NRH—CO—O—, —NRH—CO—NRH, —NRH—CS—NRH, —NRH—C(═NRH)—NRH—, —NRH—CO—CH2—NRH, —CO—O—, —O—CO—CH2—O—, —O—CH2—CO—O—, —CH2—CO—NRH—, —O—CO NRH—, —NRH—CO—CH2—, —O—CH2CH2—NRH—, —CH═N—O—, CH2—NRH—O—, —CH2—O—N═ (including R5 when used as a linkage to a succeeding monomer), —CH2—O—NRH—, —CO—NRH—CH2—, —CH2—NRH—O—, —CH2—NRH—CO—, —O—NRH—CH2—, —O—NRH—, —O—CH2—S—, —S—CH2—O—, —CH2—CH2—S—, —O—CH2—CH2—S—, —S—CH2—CH═ (including R5 when used as a linkage to a succeeding monomer), —S—CH2—CH2—, —S—CH2—CH2—O—, —S—CH2—CH2—S—, —CH2—S—CH2—, —CH2—SO—CH2—, —CH2—SO2—CH2—, —O—SO—O—, —O—S(O)2—O—, —O—S(O)2—CH2—, —O—S(O)2—NRH—, —NRH—S(O)2—CH2—, —O—S(O)2—CH2—, —O—P(O)2—O—, —O—P(O,S)—O—, —O—P(S)2—O—, —S—P(O)2—O—, —S—P(O,S)—O—, —S—P(S)2—O—, —O—P(O)2—S—, —O—P(O,S)—S—, —O—P(S)2—S—, —S—P(O)2—S—, —S—P(O,S)—S—, —S—P(S)2—S—, —O—PO(R″)—O—, —O—PO(OCH3)—O—, —O—PO(OCH2CH3)—O—, —O—PO(OCH2CH2S—R)—O—, —O—PO(BH3)—O—, —O—PO(NHRN)—O—, —O—P(O)2—NRH—, —NRH—P(O)2—O—, —O—P(O,NRH)—O—, —CH2—P(O)2—O—, —O—P(O)2—CH2—, and —O—Si(R″)2—O—; among which —CH2—CO—NRH—, —CH2—NRH—O—, —S—CH2—O—, —O—P(O)2—O—, —O—P(O,S)—O—, —O—P(S)2—O—, —NRH—P(O)2—O—, —O—P(O,NRH)—O—, —O—PO(R″)—O—, —O—PO(CH3)—O—, and —O—PO(NHRN)—O—, where RH is selected form hydrogen and C1-4-alkyl, and R″ is selected from C1-6-alkyl and phenyl, are especially desirable. Further illustrative examples are given in Mesmaeker et. al., Current Opinion in Structural Biology 1995, 5, 343-355 and Susan M. Freier and Karl-Heinz Altmann, Nucleic Acids Research, 1997, vol 25, pp 4429-4443. The left-hand side of the internucleoside linkage is bound to the 5-membered ring as substituent P* at the 3′-position, whereas the right-hand side is bound to the 5′-position of a preceding monomer.
By “LNA” or “LNA monomer” (e.g., an LNA nucleoside or LNA nucleotide) or an LNA oligomer (e.g., an oligonucleotide or nucleic acid) is meant a nucleoside or nucleotide analogue that includes at least one LNA monomer. LNA monomers as disclosed in PCT Publication WO 99/14226 are in general particularly desirable modified nucleic acids for incorporation into an oligonucleotide of the invention. Additionally, the nucleic acids may be modified at either the 3′ and/or 5′ end by any type of modification known in the art. For example, either or both ends may be capped with a protecting group, attached to a flexible linking group, attached to a reactive group to aid in attachment to the substrate surface, etc. Desirable LNA monomers and their method of synthesis also are disclosed in U.S. Pat. No. 6,043,060, U.S. Pat. No. 6,268,490, PCT Publications WO 01/07455, WO 01/00641, WO 98/39352, WO 00/56746, WO 00/56748 and WO 00/66604 as well as in the following papers: Morita et al., Bioorg. Med. Chem. Lett. 12(1):73-76, 2002; Hakansson et al., Bioorg. Med. Chem. Lett. 11(7):935-938, 2001; Koshkin et al., J. Org. Chem. 66(25):8504-8512, 2001; Kvaerno et al., J. Org. Chem. 66(16):5498-5503, 2001; Hakansson et al., J. Org. Chem. 65(17):5161-5166, 2000; Kvaerno et al., J. Org. Chem. 65(17):5167-5176, 2000; Pfundheller et al., Nucleosides Nucleotides 18(9):2017-2030, 1999; and Kumar et al., Bioorg. Med. Chem. Lett. 8(16):2219-2222, 1998.
Preferred LNA monomers, also referred to as “oxy-LNA” are LNA monomers which include bicyclic compounds as disclosed in PCT Publication WO 03/020739 wherein the bridge between R4′ and R2′ as shown in formula (I) below together designate —CH2—O— or —CH2—CH2—O—.
wherein X is selected from —O—, —S—, —N(RN)—, —C(R6R6*)—, —O—C(R7R7*)—, —C(R6R6*)—O, —S—C(R7R7*)—, —C(R6R6*)—S—, —N(RN*)—C(R7R7*)—, —C(R6R6*)—N(RN*)—, and —C(R6R6*)—C(R7R7*).
B is selected from a modified base as discussed above e.g. an optionally substituted carbocyclic aryl such as optionally substituted pyrene or optionally substituted pyrenylmethylglycerol, or an optionally substituted heteroalicylic or optionally substituted heteroaromatic such as optionally substituted pyridyloxazole, optionally substituted pyrrole, optionally substituted diazole or optionally substituted triazole moieties; hydrogen, hydroxy, optionally substituted C1-4-alkoxy, optionally substituted C1-4-alkyl, optionally substituted C1-4-acyloxy, nucleobases, DNA intercalators, photochemically active groups, thermochemically active groups, chelating groups, reporter groups, and ligands.
P designates the radical position for an internucleoside linkage to a succeeding monomer, or a 5′-terminal group, such internucleoside linkage or 5′-terminal group optionally including the substituent R5. One of the substituents R2, R2*, R3, and R3* is a group P* which designates an internucleoside linkage to a preceding monomer, or a 2′/3′-terminal group. The substituents of R1*, R4*, R5, R5*, R6, R5, R7, R7*, RN, and the ones of R2, R2*, R3, and R3* not designating P* each designates a biradical comprising about 1-8 groups/atoms selected from —C(RaRb)—, —C(Ra)═C(Ra)—, —C(Ra)═N—, —C(Ra)—O—, —O—, —Si(Ra)2—, —C(Ra)—S, —S—, —SO2—, —C(Ra)—N(Rb)—, —N(Ra)—, and >C=Q, wherein Q is selected from —O—, —S—, and —N(Ra)—, and Ra and Rb each is independently selected from hydrogen, optionally substituted C1-12-alkyl, optionally substituted C2-12-alkenyl, optionally substituted C2-12-alkynyl, hydroxy, C1-12-alkoxy, C2-12-alkenyloxy, carboxy, C1-12-alkoxycarbonyl, C1-12-alkylcarbonyl, formyl, aryl, aryloxycarbonyl, aryloxy, arylcarbonyl, heteroaryl, hetero-aryloxy-carbonyl, heteroaryloxy, heteroarylcarbonyl, amino, mono- and di(C1-6-alkyl)amino, carbamoyl, mono- and di(C1-6-alkyl)-amino-carbonyl, amino-C1-6-alkyl-aminocarbonyl, mono- and di(C1-6-alkyl)amino-C1-6-alkyl-aminocarbonyl, C1-6-alkyl-carbonylamino, carbamido, C1-6-alkanoyloxy, sulphono, C1-6-alkylsulphonyloxy, nitro, azido, sulphanyl, C1-6-alkylthio, halogen, DNA intercalators, photochemically active groups, thermochemically active groups, chelating groups, reporter groups, and ligands, where aryl and heteroaryl may be optionally substituted, and where two geminal substituents Ra and Rb together may designate optionally substituted methylene (═CH2), and wherein two non-geminal or geminal substituents selected from Ra, Rb, and any of the substituents R1*, R2, R2*, R3, R3*, R4*, R5, R5*, R6 and R6*, R7, and R7* which are present and not involved in P, P* or the biradical(s) together may form an associated biradical selected from biradicals of the same kind as defined before; the pair(s) of non-geminal substituents thereby forming a mono- or bicyclic entity together with (i) the atoms to which said non-geminal substituents are bound and (ii) any intervening atoms.
Each of the substituents R1*, R2, R2*, R3, R4*, R5, R5*, R6 and R6, R7, and R7* which are present and not involved in P, P* or the biradical(s), is independently selected from hydrogen, optionally substituted C1-2-alkyl, optionally substituted C2-12-alkenyl, optionally substituted C2-12-alkynyl, hydroxy, C2-12-alkoxy, C2-12-alkenyloxy, carboxy, C1-12-alkoxycarbonyl, C1-12-alkylcarbonyl, formyl, aryl, aryloxy-carbonyl, aryloxy, arylcarbonyl, heteroaryl, heteroaryloxy-carbonyl, heteroaryloxy, heteroarylcarbonyl, amino, mono- and di-(C1-6-alkyl)amino, carbamoyl, mono- and di(C1-16-alkyl)amino-carbonyl, amino-C1-6-alkyl-aminocarbonyl, mono- and di(C1-6-alkyl)amino-C1-6-alkyl-aminocarbonyl, C1-6-alkyl-carbonylamino, carbamido, C1-6alkanoyloxy, sulphono, C1-6-alkylsulphonyloxy, nitro, azido, sulphanyl, C1-6-alkylthio, halogen, DNA intercalators, photochemically active groups, thermochemically active groups, chelating groups, reporter groups, and ligands, where aryl and heteroaryl may be optionally substituted, and where two geminal substituents together may designate oxo, thioxo, imino, or optionally substituted methylene, or together may form a spiro biradical consisting of a 1-5 carbon atom(s) alkylene chain which is optionally interrupted and/or terminated by one or more heteroatoms/groups selected from —O—, —S—, and —(NRN)— where RN is selected from hydrogen and C1-4alkyl, and where two adjacent (non-geminal) substituents may designate an additional bond resulting in a double bond; and RN*, when present and not involved in a biradical, is selected from hydrogen and C1-4-alkyl; and basic salts and acid addition salts thereof.
Exemplary 5′, 3′, and/or 2′ terminal groups include —H, —OH, halo (e.g., chloro, fluoro, iodo, or bromo), optionally substituted aryl, (e.g., phenyl or benzyl), alkyl (e.g., methyl or ethyl), alkoxy (e.g., methoxy), acyl (e.g. acetyl or benzoyl), aroyl, aralkyl, hydroxy, hydroxyalkyl, alkoxy, aryloxy, aralkoxy, nitro, cyano, carboxy, alkoxycarbonyl, aryloxycarbonyl, aralkoxycarbonyl, acylamino, aroylamino, alkylsulfonyl, arylsulfonyl, heteroarylsulfonyl, alkylsulfinyl, arylsulfinyl, heteroarylsulfinyl, alkylthio, arylthio, heteroarylthio, aralkylthio, heteroaralkylthio, amidino, amino, carbamoyl, sulfamoyl, alkene, alkyne, protecting groups (e.g., silyl, 4,4′-dimethoxytrityl, monomethoxytrityl, or trityl(triphenylmethyl)), linkers (e.g., a linker containing an amine, ethylene glycol, quinone such as anthraquinone), detectable labels (e.g., radiolabels or fluorescent labels), and biotin.
It is understood that references herein to a nucleic acid unit, nucleic acid residue, LNA monomer, or similar term are inclusive of both individual nucleoside units and nucleotide units and nucleoside units and nucleotide units within an oligonucleotide.
A “modified base” or other similar terms refer to a composition (e.g., a non-naturally occurring nucleobase or nucleosidic base), which can pair with a natural base (e.g., adenine, guanine, cytosine, uracil, and/or thymine) and/or can pair with a non-naturally occurring nucleobase or nucleosidic base. Desirably, the modified base provides a Tm differential of 15, 12, 10, 8, 6, 4, or 2° C. or less as described herein. Exemplary modified bases are described in EP 1 072 679 and WO 97/12896.
The term “chemical moiety” refers to a part of a molecule. “Modified by a chemical moiety” thus refer to a modification of the standard molecular structure by inclusion of an unusual chemical structure. The attachment of said structure can be covalent or non-covalent.
The term “inclusion of a chemical moiety” in an oligonucleotide probe thus refers to attachment of a molecular structure. Such as chemical moiety include but are not limited to covalently and/or non-covalently bound minor groove binders (MGB) and/or intercalating nucleic acids (INA) selected from a group consisting of asymmetric cyanine dyes, DAPI, SYBR Green I, SYBR Green II, SYBR Gold, PicoGreen, thiazole orange, Hoechst 33342, Ethidium Bromide, 1-O-(1-pyrenylmethyl)glycerol and Hoechst 33258. Other chemical moieties include the modified nucleobases, nucleosidic bases or LNA modified oligonucleotides.
“Oligonucleotide analogue” refers to a nucleic acid binding molecule capable of recognizing a particular target nucleotide sequence. A particular oligonucleotide analogue is peptide nucleic acid (PNA) in which the sugar phosphate backbone of an oligonucleotide is replaced by a protein like backbone. In PNA, nucleobases are attached to the uncharged polyamide backbone yielding a chimeric pseudopeptide-nucleic acid structure, which is homomorphous to nucleic acid forms.
“High affinity nucleotide analogue” refers to a non-naturally occurring nucleotide analogue that increases the “binding affinity” of an oligonucleotide probe to its complementary recognition sequence when substituted with at least one such high-affinity nucleotide analogue.
As used herein, a probe with an increased “binding affinity” for a recognition sequence compared to a probe which comprises the same sequence but does not comprise a stabilizing nucleotide, refers to a probe for which the association constant (Ka) of the probe recognition segment is higher than the association constant of the complementary strands of a double-stranded molecule. In another preferred embodiment, the association constant of the probe recognition segment is higher than the dissociation constant (Kd) of the complementary strand of the recognition sequence in the target sequence in a double stranded molecule.
Monomers are referred to as being “complementary” if they contain nucleobases that can form hydrogen bonds according to Watson-Crick base-pairing rules (e.g. G with C, A with T or A with U) or other hydrogen bonding motifs such as for example diaminopurine with T, 5-methyl C with G, 2-thiothymidine with A, inosine with C, pseudoisocytosine with G, etc.
The term “succeeding monomer” relates to the neighbouring monomer in the 5′-terminal direction and the “preceding monomer” relates to the neighbouring monomer in the 3′-terminal direction.
The term “target nucleic acid” or “target ribonucleic acid” refers to any relevant nucleic acid of a single specific sequence, e.g., a biological nucleic acid, e.g., derived from a patient, an animal (a human or non-human animal), a plant, a bacteria, a fungi, an archae, a cell, a tissue, an organism, etc. For example, where the target ribonucleic acid or nucleic acid is derived from a bacteria, archae, plant, non-human animal, cell, fungi, or non-human organism, the method optionally further comprises selecting the bacteria, archae, plant, non-human animal, cell, fungi, or non-human organism based upon detection of the target nucleic acid. In one embodiment, the target nucleic acid is derived from a patient, e.g., a human patient. In this embodiment, the invention optionally further includes selecting a treatment, diagnosing a disease, or diagnosing a genetic predisposition to a disease, based upon detection of the target nucleic acid.
“Target sequence” refers to a specific nucleic acid sequence within any target nucleic acid.
The term “stringent conditions”, as used herein, is the “stringency” which occurs within a range from about Tm−5° C. (5° C. below the melting temperature (Tm) of the probe) to about 20° C. to 25° C. below Tm. As will be understood by those skilled in the art, the stringency of hybridization may be altered in order to identify or detect identical or related polynucleotide sequences. Hybridization techniques are generally described in Nucleic Acid Hybridization, A Practical Approach, Ed. Hames, B. D. and Higgins, S. J., IRL Press, 1985; Gall and Pardue, Proc. Natl. Acad. Sci., USA 63: 378-383, 1969; and John, et al. Nature 223: 582-587, 1969, each of which is hereby incorporated by reference. For example, stringent salt concentration will ordinarily be less than about 750 mM NaCl and 75 mM trisodium citrate, preferably less than about 500 mM NaCl and 50 mM trisodium citrate, and most preferably less than about 250 mM NaCl and 25 mM trisodium citrate. Low stringency hybridization can be obtained in the absence of organic solvent, e.g., formamide, while high stringency hybridization can be obtained in the presence of at least about 35% formamide, and most preferably at least about 50% formamide. Stringent temperature conditions will ordinarily include temperatures of at least about 30° C., more preferably of at least about 37° C., and most preferably of at least about 42° C. Varying additional parameters, such as hybridization time, the concentration of detergent, e.g., sodium dodecyl sulfate (SDS), and the inclusion or exclusion of carrier DNA, are well known to those skilled in the art. Various levels of stringency are accomplished by combining these various conditions as needed. In a preferred embodiment, hybridization will occur at 30° C. in 750 mM NaCl, 75 mM trisodium citrate, and 1% SDS. In a more preferred embodiment, hybridization will occur at 37° C. in 500 mM NaCl, 50 mM trisodium citrate, 1% SDS, 35% formamide, and 100 μg/ml denatured salmon sperm DNA (ssDNA). In a most preferred embodiment, hybridization will occur at 42° C. in 250 mM NaCl, 25 mM trisodium citrate, 1% SDS, 50% formamide, and 200 μg/ml ssDNA. Additional variations on these conditions will be readily apparent to those skilled in the art. Hybridization techniques are well known to those skilled in the art and are described, for example, in Benton and Davis (Science 196:180, 1977); Grunstein and Hogness (Proc. Natl. Acad. Sci., USA 72:3961, 1975); Ausubel et al. (Current Protocols in Molecular Biology, Wiley Interscience, New York, 2001); Berger and Kimmel (Guide to Molecular Cloning Techniques, 1987, Academic Press, New York); and Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, New York.
By “modified backbone” is meant a nucleotide backbone structure other than the naturally occurring ribose-phosphate or deoxyribose-phosphate backbones. Exemplary modified backbones include a ribonucleotide moiety that is substituted at the 2′ position. The substituents at the 2′ position may, for example, be a saturated, unsaturated, unbranched, or branched C1 to C4 alkyl group, e.g., 2′-O-methyl ribose. Another suitable example of a substituent at the 2′ position of a modified ribonucleotide moiety is a C1 to C4 alkoxy-C1 to C4 alkyl group, e.g., methoxyethyl. Another suitable example of a modified ribonucleotide moiety is a ribonucleotide that is substituted at the 2′ position with fluoro group. Preferred modified backbones also include LNA.
By two nucleotides “disposed X nucleotides apart” is meant positioned in a nucleotide sequence so that X-1 nucleotides are disposed between the two nucleotides. For example, in the sequence ACTG, the A and G are disposed three nucleotides apart.
The present invention provides novel oligonucleotide compositions and probe sequences for the use in detection, isolation, purification, amplification, identification, quantification, or capture of miRNAs, their target mRNAs, stem-loop precursor miRNAs, siRNAs, other non-coding RNAs, RNA-edited transcripts or alternative mRNA splice variants characterized in that the probe sequences contain a number of nucleoside analogues.
In a preferred embodiment the number of nucleoside analogue corresponds to from 20 to 40% of the oligonucleotide of the invention.
In a preferred embodiment the probe sequences are substituted with a nucleoside analogue with regular spacing between the substitutions
In another preferred embodiment the probe sequences are substituted with a nucleoside analogue with irregular spacing between the substitutions
In a preferred embodiment the nucleoside analogue is LNA.
In a further preferred embodiment the detection probe sequences comprise a photochemically active group, a thermochemically active group, a chelating group, a reporter group, or a ligand that facilitates the direct of indirect detection of the probe or the immobilisation of the oligonucleotide probe onto a solid support.
In a further preferred embodiment
(a) the photochemically active group, the thermochemically active group, the chelating group, the reporter group, or the ligand includes a spacer (K), said spacer comprising a chemically cleavable group; or
(b) the photochemically active group, the thermochemically active group, the chelating group, the reporter group, or the ligand is attached via the biradical of at least one of the LNA(s) of the oligonucleotide.
Preferred uses include:
(a) capture and detection of naturally occurring or synthetic single stranded nucleic acids such as miRNAs, their target mRNAs, stem-loop precursor miRNAs, siRNAs, other non-coding RNAs, RNA-edited transcripts or alternative mRNA splice variants; or
(b) purification of naturally occurring single stranded nucleic acids such as miRNAs, their target mRNAs, stem-loop precursor miRNAs, siRNAs, other non-coding RNAs, RNA-edited transcripts or alternative mRNA splice variants; or
(c) detection and assessment of expression patterns naturally occurring single stranded nucleic acids such as miRNAs, their target mRNAs, stem-loop precursor miRNAs, siRNAs, other non-coding RNAs, RNA-edited transcripts or alternative mRNA splice variants by RNA in-situ hybridisation, dot blot hybridisation, reverse Ddot blot hybridisation, or in Northern blot analysis or expression profiling by microarrays
(d) functional analysis of naturally occurring single stranded nucleic acids such as miRNAs, their target mRNAs, stem-loop precursor miRNAs, siRNAs, other non-coding RNAs, RNA-edited transcripts or alternative mRNA splice variants in vitro and in vivo in plants or animals, such as human, mouse, rat, zebrafish, Caenorhabditis elegans, Drosophila melanogaster, Arabidopsis thaliana, rice and maize, by inhibiting their mode of action, e.g. the binding of mature miRNAs to their cognate target mRNAs.
Further embodiments includes the use of an LNA modified oligonucleotide probe as an aptamer in molecular diagnostics or (b) as an aptamer in RNA mediated catalytic processes or (c) as an aptamer in specific binding of antibiotics, drugs, amino acids, peptides, structural proteins, protein receptors, protein enzymes, saccharides, polysaccharides, biological cofactors, nucleic acids, or triphosphates or (d) as an aptamer in the separation of enantiomers from racemic mixtures by stereospecific binding or (e) for labelling cells or (f) to hybridise to non-protein coding cellular RNAs, such as tRNA, rRNA, snRNA and scRNA, in vivo or in-vitro or (g) to hybridise to non-protein coding cellular RNAs, such as tRNA, rRNA, snRNA and scRNA, in vivo or in-vitro or (h) in the construction of Taqman probes or Molecular Beacons.
The present invention also provides a kit for the isolation, purification, amplification, detection, identification, quantification, or capture of natural or synthetic nucleic acids, where the kit comprises a reaction body and one or more LNAs as defined herein. The LNAs are preferably immobilised onto said reactions body (e.g. by using the immobilising techniques described above).
For the kits according to the invention, the reaction body is preferably a solid support material, e.g. selected from borosilicate glass, soda-lime glass, polystyrene, polycarbonate, polypropylene, polyethylene, polyethyleneglycol terephthalate, polyvinylacetate, polyvinylpyrrolidinone, polymethylmethacrylate and polyvinylchloride, preferably polystyrene and polycarbonate. The reaction body may be in the form of a specimen tube, a vial, a slide, a sheet, a film, a bead, a pellet, a disc, a plate, a ring, a rod, a net, a filter, a tray, a microtitre plate, a stick, or a multi-bladed stick.
A written instruction sheet stating the optimal conditions for use of the kit typically accompanies the kits.
Further Aspects of the Invention
Once the appropriate target RNA sequences have been selected, LNA substituted detection probes are preferably chemically synthesized using commercially available methods and equipment as described in the art (Tetrahedron 54: 3607-30, 1998). For example, the solid phase phosphoramidite method can be used to produce short LNA probes (Caruthers, et al., Cold Spring Harbor Symp. Quant. Biol. 47:411-418, 1982, Adams, et al., J. Am. Chem. Soc. 105: 661 (1983).
LNA-containing-probes can be labelled during synthesis. The flexibility of the phosphoramidite synthesis approach furthermore facilitates the easy production of LNAs carrying all commercially available linkers, fluorophores and labelling-molecules available for this standard chemistry. LNA-modified probes may also be labelled by enzymatic reactions e.g. by kinasing using T4 polynucleotide kinase and gamma-32P-ATP or by using terminal deoxynucleotidyl transferase (TDT) and any given digoxygenin-conjugated nucleotide triphosphate (dNTP) or dideoxynucleotide triphosphate (ddNTP).
Detection probes according to the invention can comprise single labels or a plurality of labels. In one aspect, the plurality of labels comprise a pair of labels which interact with each other either to produce a signal or to produce a change in a signal when hybridization of the detection probe to a target sequence occurs.
In another aspect, the detection probe comprises a fluorophore moiety and a quencher moiety, positioned in such a way that the hybridized state of the probe can be distinguished from the unhybridized state of the probe by an increase in the fluorescent signal from the nucleotide. In one aspect, the detection probe comprises, in addition to the recognition element, first and second complementary sequences, which specifically hybridize to each other, when the probe is not hybridized to a recognition sequence in a target molecule, bringing the quencher molecule in sufficient proximity to said reporter molecule to quench fluorescence of the reporter molecule. Hybridization of the target molecule distances the quencher from the reporter molecule and results in a signal, which is proportional to the amount of hybridization.
In the present context, the term “label” means a reporter group, which is detectable either by itself or as a part of a detection series. Examples of functional parts of reporter groups are biotin, digoxigenin, fluorescent groups (groups which are able to absorb electromagnetic radiation, e.g. light or X-rays, of a certain wavelength, and which subsequently reemits the energy absorbed as radiation of longer wavelength; illustrative examples are DANSYL (5-dimethylamino)-1-naphthalenesulfonyl), DOXYL (N-oxyl-4,4-dimethyloxazolidine), PROXYL (N-oxyl-2,2,5,5-tetramethylpyrrolidine), TEMPO(N-oxyl-2,2,6,6-tetramethylpiperidine), dinitrophenyl, acridines, coumarins, Cy3 and Cy5 (trademarks for Biological Detection Systems, Inc.), erythrosine, coumaric acid, umbelliferone, Texas red, rhodamine, tetramethyl rhodamine, Rox, 7-nitrobenzo-2-oxa-1-diazole (NBD), pyrene, fluorescein, Europium, Ruthenium, Samarium, and other rare earth metals), radio isotopic labels, chemiluminescence labels (labels that are detectable via the emission of light during a chemical reaction), spin labels (a free radical (e.g. substituted organic nitroxides) or other paramagnetic probes (e.g. Cu2+, Mg2+) bound to a biological molecule being detectable by the use of electron spin resonance spectroscopy). Especially interesting examples are biotin, fluorescein, Texas Red, rhodamine, dinitrophenyl, digoxigenin, Ruthenium, Europium, Cy5, Cy3, etc.
Suitable samples of target nucleic acid molecules may comprise a wide range of eukaryotic and prokaryotic cells, including protoplasts; or other biological materials, which may harbour target nucleic acids. The methods are thus applicable to tissue culture animal cells, animal cells (e.g., blood, serum, plasma, reticulocytes, lymphocytes, urine, bone marrow tissue, cerebrospinal fluid or any product prepared from blood or lymph) or any type of tissue biopsy (e.g. a muscle biopsy, a liver biopsy, a kidney biopsy, a bladder biopsy, a bone biopsy, a cartilage biopsy, a skin biopsy, a pancreas biopsy, a biopsy of the intestinal tract, a thymus biopsy, a mammae biopsy, a uterus biopsy, a testicular biopsy, an eye biopsy or a brain biopsy, e.g., homogenized in lysis buffer), archival tissue nucleic acids, plant cells or other cells sensitive to osmotic shock and cells of bacteria, yeasts, viruses, mycoplasmas, protozoa, rickettsia, fungi and other small microbial cells and the like.
Preferably, the detection probes of the invention are modified in order to increase the binding affinity of the probes for the target sequence by at least two-fold compared to probes of the same sequence without the modification, under the same conditions for hybridization or stringent hybridization conditions. The preferred modifications include, but are not limited to, inclusion of nucleobases, nucleosidic bases or nucleotides that have been modified by a chemical moiety or replaced by an analogue to increase the binding affinity. The preferred modifications may also include attachment of duplex-stabilizing agents e.g., such as minor-groove-binders (MGB) or intercalating nucleic acids (INA). Additionally, the preferred modifications may also include addition of non-discriminatory bases e.g., such as 5-nitroindole, which are capable of stabilizing duplex formation regardless of the nucleobase at the opposing position on the target strand. Finally, multi-probes composed of a non-sugar-phosphate backbone, e.g. such as PNA, that are capable of binding sequence specifically to a target sequence are also considered as a modification. All the different binding affinity-increasing modifications mentioned above will in the following be referred to as “the stabilizing modification(s)”, and the tagging probes and the detection probes will in the following also be referred to as “modified oligonucleotide”. More preferably the binding affinity of the modified oligonucleotide is at least about 3-fold, 4-fold, 5-fold, or 20-fold higher than the binding of a probe of the same sequence but without the stabilizing modification(s).
Most preferably, the stabilizing modification(s) is inclusion of one or more LNA nucleotide analogs. Probes from 6 to 30 nucleotides according to the invention may comprise from 1 to 8 stabilizing nucleotides, such as LNA nucleotides. When at least two LNA nucleotides are included, these may be consecutive or separated by one or more non-LNA nucleotides. In one aspect, LNA nucleotides are alpha and/or xylo LNA nucleotides.
The problems with existing detection, quantification and knock-down of miRNAs and siRNAs as outlined above are addressed by the use of the novel oligonucleotide probes of the invention in combination with any of the methods of the invention selected so as to recognize or detect a majority of all discovered and detected miRNAs, in a given cell type from a given organism. In one aspect, the probe sequences comprise probes that detect mammalian mature miRNAs, e.g., such as mouse, rat, rabbit, monkey, or human miRNAs. By providing a sensitive and specific method for detection of mature miRNAs, the present invention overcomes the limitations discussed above especially for conventional miRNA assays and siRNA assays. The detection element of the detection probes according to the invention may be single or double labelled (e.g. by comprising a label at each end of the probe, or an internal position). In one aspect, the detection probe comprises two labels capable of interacting with each other to produce a signal or to modify a signal, such that a signal or a change in a signal may be detected when the probe hybridizes to a target sequence. A particular aspect is when the two labels comprise a quencher and a reporter molecule.
In another aspect, the probe comprises a target-specific recognition segment capable of specifically hybridizing to a target molecule comprising the complementary recognition sequence. A particular detection aspect of the invention referred to as a “molecular beacon with a stem region” is when the recognition segment is flanked by first and second complementary hairpin-forming sequences which may anneal to form a hairpin. A reporter label is attached to the end of one complementary sequence and a quenching moiety is attached to the end of the other complementary sequence. The stem formed when the first and second complementary sequences are hybridized (i.e., when the probe recognition segment is not hybridized to its target) keeps these two labels in close proximity to each other, causing a signal produced by the reporter to be quenched by fluorescence resonance energy transfer (FRET). The proximity of the two labels is reduced when the probe is hybridized to a target sequence and the change in proximity produces a change in the interaction between the labels. Hybridization of the probe thus results in a signal (e.g. fluorescence) being produced by the reporter molecule, which can be detected and/or quantified.
The invention also provides a method, system and computer program embedded in a computer readable medium (“a computer program product”) for designing detection probes comprising at least one stabilizing nucleobase. The method comprises querying a database of target sequences (e.g., such as the miRNA registry at http://www.sanger.ac.uk/Software/Rfam/mirna/index.shtml) and designing probes which: i) have sufficient binding stability to bind their respective target sequence under stringent hybridization conditions, ii) have limited propensity to form duplex structures with itself, and iii) are capable of binding to and detecting/quantifying at least about 60%, at least about 70%, at least about 80%, at least about 90% or at least about 95% of all the target sequences in the given database of miRNAs or other RNA sequences.
In one preferred aspect, the target sequence database comprises nucleic acid sequences corresponding to human, mouse, rat, Drosophila melanogaster, C. elegans, Arabidopsis thaliana, maize or rice miRNAs.
In another aspect, the method further comprises calculating stability based on the assumption that the recognition sequence comprises at least one stabilizing nucleotide, such as an LNA molecule. In one preferred aspect the calculated stability is used to eliminate probes with inadequate stability from the database of virtual candidate probes prior to the initial query against the database of target sequence to initiate the identification of optimal probe recognition sequences.
In another aspect, the method further comprises calculating the capability for a given probe sequence to form a duplex structure with itself based on the assumption that the sequence comprises at least one stabilizing nucleotide, such as an LNA molecule. In one preferred aspect the calculated propensity is used to eliminate probe sequences that are likely to form probe duplexes from the database of virtual candidate probes.
A preferred embodiment of the invention are kits for the detection or quantification of target miRNAs, siRNAs, RNA-edited transcripts, non-coding antisense transcripts or alternative splice variants comprising libraries of detection probes. In one aspect, the kit comprises in silico protocols for their use. The detection probes contained within these kits may have any or all of the characteristics described above. In one preferred aspect, a plurality of probes comprises at least one stabilizing nucleotide, such as an LNA nucleotide. In another aspect, the plurality of probes comprises a nucleotide coupled to or stably associated with at least one chemical moiety for increasing the stability of binding of the probe. The kits according to the invention allow a user to quickly and efficiently develop an assay for different miRNA targets, siRNA targets, RNA-edited transcripts, non-coding antisense transcripts or alternative splice variants.
In general, the invention features the design of high affinity oligonucleotide probes that have duplex stabilizing properties and methods highly useful for a variety of target nucleic acid detection methods (e.g., monitoring spatiotemporal expression of microRNAs or siRNAs or knock-down of miRNAs). Some of these oligonucleotide probes contain novel nucleotides created by combining specialized synthetic nucleobases with an LNA backbone, thus creating high affinity oligonucleotides with specialized properties such as reduced sequence discrimination for the complementary strand or reduced ability to form intramolecular double stranded structures. The invention also provides improved methods for detecting and quantifying ribonucleic acids in complex nucleic acid sample. Other desirable modified bases have decreased ability to self-anneal or to form duplexes with oligonucleotide probes containing one or more modified bases.
The invention will now be further illustrated with reference to the following examples. It will be appreciated that what follows is by way of example only and that modifications to detail may be made while still falling within the scope of the invention.
The LNA-substituted probes of Example 2 to 11 were prepared on an automated DNA synthesizer (Expedite 8909 DNA synthesizer, PerSeptive Biosystems, 0.2 μmol scale) using the phosphoramidite approach (Beaucage and Caruthers, Tetrahedron Lett. 22: 1859-1862, 1981) with 2-cyanoethyl protected LNA and DNA phosphoramidites, (Sinha, et al., Tetrahedron Lett. 24: 5843-5846, 1983). CPG solid supports derivatised with a suitable quencher and 5′-fluorescein phosphoramidite (GLEN Research, Sterling, Va., USA). The synthesis cycle was modified for LNA phosphoramidites (250s coupling time) compared to DNA phosphoramidites. 1H-tetrazole or 4,5-dicyanoimidazole (Proligo, Hamburg, Germany) was used as activator in the coupling step.
The probes were deprotected using 32% aqueous ammonia (1h at room temperature, then 2 hours at 60° C.) and purified by HPLC (Shimadzu-SpectraChrom series; Xterra™ RP18 column, 10?m 7.8×150 mm (Waters). Buffers: A: 0.05M Triethylammonium acetate pH 7.4. B. 50% acetonitrile in water. Eluent: 0-25 min: 10-80% B; 25-30 min: 80% B). The composition and purity of the probes were verified by MALDI-MS (PerSeptive Biosystem, Voyager DE-PRO) analysis.
List of LNA-substituted detection probes for detection of fully conserved vertebrate microRNAs in all vertebrates. LNA nucleotides are depicted by capital letters, DNA nucleotides by lowercase letters, mC denotes LNA methylcytosine. The detection probes can be used to detect and analyze conserved vertebrate miRNAs by RNA in situ hybridization, Northern blot analysis and by silencing using the probes as miRNA inhibitors. The LNA-modified probes can be conjugated with a variety of haptens or fluorochromes for miRNA in situ hybridization using standard methods. 5′-end labeling using T4 polynucleotide kinase and gamma-32P-ATP can be carried out by standard methods for Northern blot analysis. In addition, the LNA-modified probe sequences can be used as capture sequences for expression profiling by LNA oligonucleotide microarrays. Covalent attachment to the solid surfaces of the capture probes can be accomplished by incorporating a NH2-C6- or a NH2-C6-hexaethylene glycol monomer or dimer group at the 5′-end or at the 3′-end of the probes during synthesis.
List of LNA-substituted detection probes for detection of fully conserved vertebrate microRNAs in all vertebrates. LNA nucleotides are depicted by capital letters, DNA nucleotides by lowercase letters, mC denotes LNA methylcytosine. The detection probes can be used to detect and analyze conserved vertebrate miRNAs by RNA in situ hybridization, Northern blot analysis and by silencing using the probes as miRNA inhibitors. The LNA-modified probes can be conjugated with a variety of haptens or fluorochromes for miRNA in situ hybridization using standard methods. 5′-end labeling using T4 polynucleotide kinase and gamma-32P-ATP can be carried out by standard methods for Northern blot analysis. In addition, the LNA-modified probe sequences can be used as capture sequences for expression profiling by LNA oligonucleotide microarrays. Covalent attachment to the solid surfaces of the capture probes can be accomplished by incorporating a NH2-C6- or a NH2-C6-hexaethylene glycol monomer or dimer group at the 5′-end or at the 3′-end of the probes during synthesis.
List of LNA-substituted detection probes for detection of zebrafish microRNAs. LNA nucleotides are depicted by capital letters, DNA nucleotides by lowercase letters, mC denotes LNA methyl-cytosine. The detection probes can be used to detect and analyze conserved vertebrate miRNAs by RNA in situ hybridization, Northern blot analysis and by silencing using the probes as miRNA inhibitors. The LNA-modified probes can be conjugated with a variety of haptens or fluorochromes for miRNA in situ hybridization using standard methods. 5′-end labeling using T4 polynucleotide kinase and gamma-32P-ATP can be carried out by standard methods for Northern blot analysis. In addition, the LNA-modified probe sequences can be used as capture sequences for expression profiling by LNA oligonucleotide microarrays. Covalent attachment to the solid surfaces of the capture probes can be accomplished by incorporating a NH2-C6- or a NH2-C6-hexaethylene glycol monomer or dimer group at the 5′-end or at the 3′-end of the probes during synthesis.
List of LNA-substituted detection probes for detection of drosophila melanogaster microRNAs. LNA nucleotides are depicted by capital letters, DNA nucleotides by lowercase letters, mC denotes LNA methyl-cytosine. The detection probes can be used to detect and analyze conserved vertebrate miRNAs by RNA in situ hybridization, Northern blot analysis and by silencing using the probes as miRNA inhibitors. The LNA-modified probes can be conjugated with a variety of haptens or fluorochromes for miRNA in situ hybridization using standard methods. 5′-end labeling using T4 polynucleotide kinase and gamma-32P-ATP can be carried out by standard methods for Northern blot analysis. In addition, the LNA-modified probe sequences can be used as capture sequences for expression profiling by LNA oligonucleotide microarrays. Covalent attachment to the solid surfaces of the capture probes can be accomplished by incorporating a NH2-C6- or a NH2-C6-hexaethylene glycol monomer or dimer group at the 5′-end or at the 3′-end of the probes during synthesis.
List of LNA-substituted detection probes for detection of Drosophila melanogaster and Caenorhabditis elegans microRNAs. LNA nucleotides are depicted by capital letters, DNA nucleotides by lowercase letters, mC denotes LNA methyl-cytosine. The detection probes can be used to detect and analyze conserved vertebrate miRNAs by RNA in situ hybridization, Northern blot analysis and by silencing using the probes as miRNA inhibitors. The LNA-modified probes can be conjugated with a variety of haptens or fluorochromes for miRNA in situ hybridization using standard methods. 5′-end labeling using T4 polynucleotide kinase and gamma-32P-ATP can be carried out by standard methods for Northern blot analysis. In addition, the LNA-modified probe sequences can be used as capture sequences for expression profiling by LNA oligonucleotide microarrays. Covalent attachment to the solid surfaces of the capture probes can be accomplished by incorporating a NH2-C6- or a NH2-C6-hexaethylene glycol monomer or dimer group at the 5′-end or at the 3′-end of the probes during synthesis.
List of LNA-substituted detection probes for detection of Arabidopsis thaliana microRNAs. LNA nucleotides are depicted by capital letters, DNA nucleotides by lowercase letters, mC denotes LNA methyl-cytosine. The detection probes can be used to detect and analyze conserved vertebrate miRNAs by RNA in situ hybridization, Northern blot analysis and by silencing using the probes as miRNA inhibitors. The LNA-modified probes can be conjugated with a variety of haptens or fluorochromes for miRNA in situ hybridization using standard methods. 5′-end labeling using T4 polynucleotide kinase and gamma-32P-ATP can be carried out by standard methods for Northern blot analysis. In addition, the LNA-modified probe sequences can be used as capture sequences for expression profiling by LNA oligonucleotide microarrays. Covalent attachment to the solid surfaces of the capture probes can be accomplished by incorporating a NH2-C6- or a NH2-C6-hexaethylene glycol monomer or dimer group at the 5′-end or at the 3′-end of the probes during synthesis.
List of LNA-substituted detection probes for detection of Arabidopsis thaliana microRNAs. LNA nucleotides are depicted by capital letters, DNA nucleotides by lowercase letters, mC denotes LNA methyl-cytosine. The detection probes can be used to detect and analyze conserved vertebrate miRNAs by RNA in situ hybridization, Northern blot analysis and by silencing using the probes as miRNA inhibitors. The LNA-modified probes can be conjugated with a variety of haptens or fluorochromes for miRNA in situ hybridization using standard methods. 5′-end labeling using T4 polynucleotide kinase and gamma-32P-ATP can be carried out by standard methods for Northern blot analysis. In addition, the LNA-modified probe sequences can be used as capture sequences for expression profiling by LNA oligonucleotide microarrays. Covalent attachment to the solid surfaces of the capture probes can be accomplished by incorporating a NH2-C6- or a NH2-C6-hexaethylene glycol monomer or dimer group at the 5′-end or at the 3′-end of the probes during synthesis.
List of LNA-substituted detection probes useful as negative controls in detection of vertebrate microRNAs. LNA nucleotides are depicted by capital letters, DNA nucleotides by lowercase letters, mC denotes LNA methyl-cytosine. The detection probes can be used to detect and analyze conserved vertebrate miRNAs by RNA in situ hybridization, Northern blot analysis and by silencing using the probes as miRNA inhibitors. The LNA-modified probes can be conjugated with a variety of haptens or fluorochromes for miRNA in situ hybridization using standard methods. 5′-end labeling using T4 polynucleotide kinase and gamma-32P-ATP can be carried out by standard methods for Northern blot analysis. In addition, the LNA-modified probe sequences can be used as capture sequences for expression profiling by LNA oligonucleotide microarrays. Covalent attachment to the solid surfaces of the capture probes can be accomplished by incorporating a NH2-C6- or a NH2-C6-hexaethylene glycol monomer or dimer group at the 5′-end or at the 3′-end of the probes during synthesis.
List of LNA-substituted detection probes for detection of human microRNAs. LNA nucleotides are depicted by capital letters, DNA nucleotides by lowercase letters, mC denotes LNA methyl-cytosine, PM perfect match to the miRNA, MM one mismatch at the central position of the probe sequence. The detection probes can be used to detect and analyze conserved vertebrate miRNAs by RNA in situ hybridization, Northern blot analysis and by silencing using the probes as miRNA inhibitors. The LNA-modified probes can be conjugated with a variety of haptens or fluorochromes for miRNA in situ hybridization using standard methods. 5′-end labeling using T4 polynucleotide kinase and gamma-32P-ATP can be carried out by standard methods for Northern blot analysis. In addition, the LNA-modified probe sequences can be used as capture sequences for expression profiling by LNA oligonucleotide microarrays. Covalent attachment to the solid surfaces of the capture probes can be accomplished by incorporating a NH2-C6- or a NH2-C6-hexaethylene glycol monomer or dimer group at the 5′-end or at the 3′-end of the probes during synthesis.
LNA nucleotides are depicted by capital letters, DNA nucleotides by lowercase letters, mC denotes LNA methyl-cytosine, PM perfect match to the miRNA, MM one mismatch at the central position of the probe sequence, dir denotes the probe sequence corresponding to the mature miRNA sequence, rev denotes the probe sequence complementary to the mature miRNA sequence in question. The detection probes can be used t as capture sequences for expression profiling by LNA oligonucleotide microarrays. Covalent attachment to the solid surfaces of the capture probes can be accomplished by incorporating a NH2—C6- or a NH2—C6-hexaethylene glycol monomer or dimer group at the 5′-end or at the 3′-end of the probes during synthesis.
In order to address miRNA function in myoblastic differentiation, we designed a loss-of-function assay based on antisense oligonucleotides complementary to the miRNA sequence. Antisense oligonucleotides have been used to demonstrate a function for miRNAs in drosophila (Boutla et al., 2003). Antisense oligonucleotides with a 2′-O-methyl modification have been shown to block RISC activity (Hutvagner et al., 2004; Meister et al., 2004). We chose to use oligonucleotides containing locked nucleotides (LNAs) (Kumar et al., 1998). These form highly stable duplexes with complementary RNAs (Koshkin, 1998), even when using short sequences (Kurreck et al., 2002). They trigger the degradation of target mRNAs by RNase H, provided that the locked nucleotides are not located at the center of the sequence. (Wahlestedt et al., 2000). A stable interaction between the antisense oligonucleotide and the miRNA would be expected to facilitate the sequestration of the miRNA in a duplex unable to interact with cellular protein complexes such as RISC or the miRNPs, or to anneal with complementary target mRNAs. Alternatively, it could induce the degradation of the miRNA by RNase H, similar to what was described for LNA/DNA oligonucleotides targetting mRNAs. Mixed LNA/DNA oligonucleotides with LNAs located either at the center or at the extremities of the sequence were transfected into myoblatsts, and mRNAs were analyzed by northern blotting. Results (
We favour a hypothesis in which the LNA/DNA oligonucleotides form a highly stable duplex with the miRNA, that subsequently resists the denaturing conditions used for northern blot, thereby preventing microRNA detection. Supporting this hypothesis, in some experiments we observed a faint smear migrating above the miRNA position that might correspond to melting miRNA/LNA duplexes (see for example
MiR-181 has been described as having a role in B lymphocytes, and its upregulation during skeletal muscle differentiation ex vivo and during muscle regeneration in vivo (
Inhibition is Rescued by miR-181
The level of expression achieved with a plasmid designed as previously described (Zeng et al., 2002) was very low. Rescue experiments were therefore performed by co-transfecting the miRNA as a synthetic sequence. When cotransfected with the LNA, synthetic miR-181 was able to restore a significant level of differentiation in transfected cells, as assessed by the number of myotubes (
In mammals, miRNA targets have been predicted in silico (Lewis et al., 2003), but have been validated in a very limited number of cases. Among the potential targets identified in silico for miR181, some may be relevant to muscle. In particular, Hoxa11, a homeodomain protein that is essential for limb (Small and Potter, 1993) and kidney formation (Patterson et al., 2001), is a repressor of MyoD function (Yamamoto and Kuroiwa, 2003). Immunofluorescence analysis demonstrated that it is expressed in nuclei of adult resting muscle, confirming previous observations (Takahashi et al., 2004), but is undetectable in regenerating muscle (
Myoblastic C2C12 cells were maintained in Dulbecco's minimal essential medium (DMEM), (Life Technologies, Inc.) supplemented with 15% fetal bovine serum (Dominique Dutscher). For transfections, 5×104 cells were plated in 6-well plates and transfected the next day with 1 μg of oligonucleotides using Lipofectamine (Invitrogen). To induce terminal differentiation, 24 h after transfection, growth medium was replaced by differentiation medium (DMEM, 2% horse serum, Sigma). Phenotypic differentiation was observed after 72-96 h.
Mouse ES cells (kind gift or Dr. Muriel Vernet) were cultured and maintained in an undifferentiated state as described (Zhuang et al., 1992). For embryoid body (EB) formation they were diluted and kept in suspension for 4 days. To induce muscle differentiation EB were maintained an additional 2 days in presence of 1% DMSO in DMEM with 10% horse serum, then plated on tissue culture dishes in DMEM with 2% horse serum. Myotubes were observed at 21 days of differentiation.
6 to 7 week-old Balb/c mice were put to sleep with Avertin as described in (Weiss and Zimmermann, 1999), the leg was shaved, and injections were made into the tibialis anterior (TA) muscle, using a 29 G1/2 insulin syringe. Cardiotoxin (Latoxan) was diluted to 10 μM in PBS, and 25 μl were injected per TA muscle (Hosaka et al., 2002). Control animals received equal volumes of PBS. TA muscles were harvested at different time points, and total RNA was extracted and used for northern blot.
SiRNA, RNA, DNA and LNA/DNA mixed oligonucleotides were obtained from Proligo, France.
Northern Blot
For northern blot analysis 30 μg of total RNA were separated in 15% denaturating polyacrylamide gels and electro-transferred to Hybond-N+ membranes. DNA anti-sense probes were end-labeled with T4 polynucleotide kinase (BioLabs) using γ-32P-ATP with high specific activity (7000 Ci/mmol, ICN). Hybridization and washing were carried out in Rapid-hyb buffer (Amersham) at 42° C. U6 expression was tested as loading control.
In Situ Hybridization
The miRNAin situ hybridization protocol by Ambion was optimized for skeletal muscle. Briefly, the tibialis anterior (TA) muscle was frozen in Tissue-Tek OCT reagent, cryo-sections (12 μM) were prepared, de-proteinized and acetylated as described in (DeNardi et al., 1993). Digoxigenin (DIG)—labeled miRNA probes (miR181: sequence complementary to the mature miRNA) were prepared according to the instructions for the mirVana Probe Construction kit (Ambion). Muscle sections were incubated with specific miRNA probes (500 ng/ml) overnight at 380° C., washed with 2×SSC at 38° C. for 20 min, and treated with 400 unit/ml (10 μg/ml) RNase A at 37° C. for 30 min. After two washes with PBS, the slides were incubated with FITC-coupled anti-DIG antibody (Roche) for 4 hours at room temperature, washed, rinsed with 200 ng/ml Hoecsht 33258 in PBS, mounted on glass slides with VectaShield (BioValley), and analyzed by fluorescent microscopy.
Western Blot and Immunofluorescence
Western blot and immunostaining were performed as described previously (Polesskaya et al., 2001). Rabbit anti-MCK was kindly provided by Dr. Hidenory Ito, anti Hox-a11 was a kind gift of Larry Patterson, anti-MHC (MY-32) and Cy-3 conjugated anti-mouse IgG were purchased from Sigma.
In-Vitro Analysis of miRNA/LNA Duplexes
Synthetic miR-181 a RNA was end-labeled with 32P-ATP using T4 polynucleotide kinase, purified on a G-25 column and mixed with cold miR-181 so that the final activity was 105 cpm/μmol RNA. 10 μmol of labeled miR-181 were mixed with increasing amounts of LNA oligonucleotides in a total volume of 20 μl of DEPC-treated water containing 1 U/μl Rnase Inhibitor (Life Technologies). After 15 min incubation at room temperature, 10 μl of the olignucleotide mixture was mixed with 2× Urea loading buffer, incubated 15 min at 65° C. and separated on a 15% denaturating polyacrylamide gel. RNAs were electro-transferred to Hybond19 N+ membranes. Free RNA and complexes were detected by autoradiography. The 32P-labeled molecular weight ladder was purchased from Ambion.
Deciphering the mechanisms underlying skeletal muscle-cell differentiation in mammals is an important challenge. Cell differentiation involves complex pathways regulated at both transcriptional and post-transcriptional levels. Recent observations have revealed the importance of small (20-25 base pair) non-coding RNAs (microRNAs or miRNAs) that are expressed in both lower organisms1 and in mammals2,3. miRNAs modulate gene expression by affecting mRNA translation4 or stability5. In lower organisms, miRNAs are essential for cell differentiation during development6-9; some miRNAs are involved in maintenance of the differentiated state. Here, we show that miR-181, a microRNA that is strongly upregulated during differentiation, participates in establishing the muscle phenotype. Moreover, our results suggest that miR-181 downregulates the homeobox protein Hox-A11 (a repressor of the differentiation process), thus establishing a functional link between miR-181 and the complex process of mammalian skeletal-muscle differentiation. Therefore, miRNAs can be involved in the establishment of a differentiated phenotype—even when they are not expressed in the corresponding fully differentiated tissue.
Muscle precursors, or myoblasts, are derived from multipotent precursor cells and acquire the myoblastic phenotype during the first step of skeletal muscle differentiation. They subsequently exit from the cell cycle and enter terminal differentiation, fusing into large multinucleated myotubes and expressing muscle-specific marker proteins. Differentiation can be partially recapitulated in two in vitro models: using either totipotent embryonic stem cells oriented toward the muscle lineage10, or established myoblastic cell lines that enter the skeletal muscle differentiation pathway by default when they are deprived of growth factors.
We screened for miRNAs that were differentially expressed during the two main steps of muscle differentiation and found that miR-181 is one of the most strongly upregulated miRNAs when terminal differentiation is induced in either of the two models. In myoblastic cells, miR-181 is upregulated before, or concomitant with, expression of differentiation-specific proteins such as muscle creatine kinase (MCK;
In vivo, miR-181 was barely detectable in the tibialis anterior muscle of adult mouse, as previously described9,12, but was strongly upregulated on regeneration of muscle fibres (
Together, these data indicate that miR-181, though poorly expressed in terminally differentiated muscle, is highly expressed in regenerating muscle, and raised the possibility that it may function during muscle differentiation. To address this issue, we designed an antisense-based loss-of-function assay13,14 using LNA-DNA-mixed-antisense oligonucleotides15: these oligonucleotides form highly stable sequence-specific duplexes with their target miRNA sequences, and are potent, specific and long-lasting inhibitors of these molecules. An LNA-DNA antisense oligonucleotide complementary to miR-181a (for sequence, see
The miR-181 antisense LNA oligonucleotides dramatically affected C2C12 myoblast differentiation, as assessed by both myotube formation and by the expression of sarcomeric myosin heavy chain (MHC;
During differentiation of C2C12 cells in vitro, MyoD induces myogenin and triggers the entire differentiation programme. In miR-181-depleted C2C12 cells, MyoD expression was inhibited (
In differentiating C2C12 cells, despite reduced Hox-A11 protein levels, a concomitant decrease in Hox-A11 mRNA (
Taken together, our data indicate that Hox-A11 is a direct target of miR-181 during mammalian muscle differentiation. This was confirmed at the functional level by simultaneously inhibiting miR-181 and Hox-A11; an siRNA against Hox-A11 partly rescued the differentiation phenotype created by the anti-miR-181 antisense LNA oligonucleotide (
Our results also suggest that Hox-A 11 is not the only target of miR-181. First, restoration of the LNA-induced differentiation phenotype by treatment with anti-Hox-A11 siRNA was only partial (
Taken together, our data demonstrate that miR-181 is required for skeletal myoblast terminal differentiation, during which an important target is the homeobox protein Hox-A11. However, neither upregulation of miR-181, nor downregulation of Hox-A11, triggered terminal differentiation of proliferating myoblasts (
DNA constructs. The reporter plasmid containing the miR-181a complementary sequence was constructed by inserting a synthetic double-stranded oligonucleotide into the SalI-XbaI site of pISO vector (kind gift of D. Bartel) downstream of the firefly luciferase coding sequence. Reporter plasmids with four copies of the pre-dicted Hox-A11 target sequence for miR-181 (position of the binding nucleus, 1361 in mRNA, NM—005523), either wild type or mutated, were constructed by cloning four tandem repeats of a 64 base pair sequence containing the target into the Sal I-XbaI sites of pISO. Details of construction are available on request. The pISO reporter plasmid containing the miR196 target site from Hox-B8 was a kind gift of D. Bartel.
Oligonucleotides. SiRNA, RNA, and DNA oligonucleotides were obtained from various sources; LNA probes discriminating miR-181a, b and c isoforms were from Exiquon (Vedbaek, Denmark). LNA-DNA mixed oligonucleotides were from Proligo (Paris, France). The anti-Hox-AII siRNA sequence was: 5′-GAGCUCGGCCAACGUCUACTT-3′.
Cell culture and transfection. Myoblast C2C12 cells were maintained in Dulbecco's minimal essential medium (DMEM; Gibco-Invitrogen, Paisley, UK) supplemented with 15% fetal bovine serum (Dominique Dutscher, Brumath, France). For transfections, 5×104 cells were plated in 6-well plates and transfected the next day with 1 μg of oligonucleotides using Lipofectamine (Gibco-Invitrogen). To induce terminal differentiation, 24 h after transfection, growth medium was replaced by differentiation medium (DMEM, 2% horse serum, Invitrogen). Phenotypic differentiation was observed after 72-96 h. For luciferase assays, HeLa S3 cells were grown in complete DMEM in 24-well plates. Cells were transfected, using Lipofectamine 2000, with firefly luciferase reporter vectors (0.05 μg), together with a Renilla luciferase control vector (0.1 μg) (Promega, Lyon, France) and equal amounts (as assessed by A260 and by gel analysis) of synthetic miRNA duplexes (0.1 μg). Luciferase activity was measured 24 h post transfection and was normalized using Renilla luciferase activity. C2C12 cells were transfected with firefly luciferase reporter constructs containing a sequence complementary to miR-181 in their 3′ UTR, or a mutated version of this sequence, along with a Renilla construct to monitor transfection efficiency, and placed under differentiation conditions; reporter activities were measured after 2 days in differentiation medium.
Mouse embryonic stem cells (kind gift of M. Vernet) were cultured and maintained in an undifferentiated state using standard procedures. For embryoid body formation they were diluted and kept in suspension for 4 days. To induce muscle differentiation, embryoid bodies were maintained an additional 2 days in 1% DMSO in DMEM with 10% horse serum10, then plated on tissue culture dishes in DMEM with 2% horse serum. Myotubes were observed at 21 days of differentiation.
Cardiotoxin-induced regeneration assay. Six- to seven-week-old Balb/c mice were anaesthetized with Avertin (Sigma-Aldrich, Steinheim, Germany), the leg was shaved, and injections were made into the tibialis anterior muscle, using a 29 G ½ insulin syringe. Cardiotoxin (Latoxan, Valence, France) was diluted to 10 μM in PBS, and 25 μl were injected per muscle29. Control animals received equal volumes of PBS. Tibialis anterior muscles were harvested at different times, and total RNA was extracted and used for northern blots, or muscles were frozen as described below for in situ hybridization.
Northern blot. For northern blot analyses, 30 μg of total RNA were separated on 15% denaturing polyacrylamide gels and electro-transferred to Hybond-N+ (Amersham Biosciences, Little Chalfont, UK) membranes. DNA anti-sense probes were end-labelled with T4 polynucleotide kinase (BioLabs, Hitchin, UK) using γ-32P-ATP with high specific activity (6,000 Ci mmol-1, Amersham Biosciences). Hybridization was carried out in Rapid-hyb buffer (Amersham Biosciences) at 42° C. Washing was carried out at 42° C. (DNA probes) or at 65° C. (LNA probes). U6 expression was used as a loading control.
In situ hybridization and immuno-FISH. The miRNA in situ hybridization protocol by Ambion (Austin, Tex.) was optimized for skeletal muscle. Briefly, the tibialis anterior muscle was frozen in Tissue-Tek OCT reagent, cryo-sections (12 μm) were prepared, de-proteinized and acetylated as previously described30. Digoxigenin (DIG)-labelled miRNA probes (miR-181: sequence complementary to the mature miRNA) were prepared according to the instructions for the mirVana Probe Construction kit (Ambion). Muscle cross-sections were incubated with specific miRNA probes (500 ng/ml) overnight at 38° C., washed with 2. SSC at 38° C. for 20 min, and treated with 400 units/ml (10 μg/ml) RNase A at 37° C. for 30 min. After two washes with PBS, the slides were incubated with FITC-coupled anti-DIG antibody (Roche, Mannheim, Germany) for 4 h at room temperature, washed, rinsed with 200 ng/ml DAPI in PBS, mounted on glass slides with VectaShield (BioValley, Burlingame, Calif.), and analysed by fluorescent microscopy.
For immuno-FISH experiments, the cryo-sections were fixed with 4% phosphate-buffered paraformaldehyde (PFA) for 10 min, treated for 10 min with 1 μg/ml proteinase K, and post-fixed in 4% PFA for 10 more min. In situ hybridization was performed as described above, and then the sections were incubated 4 h to overnight at room temperature with anti-embryonic MHC antibody (F1.652, Developmental Studies Hybridoma Bank, Iowa City, Iowa), at 2 μg/ml in PBS-1% BSA-5% newborn calf serum. Detection was performed by 1 h incubation with anti-mouse-TRITC anti-body (Sigma-Aldrich), diluted 1:1,000 in blocking solution.
For all FISH and immuno-FISH experiments, 25-30 cross-sections from four independent regenerating tibialis anterior muscles were analysed. Negative controls with secondary antibodies alone were performed in all cases, and gave no detectable staining.
Real-time RT-PCR. Poly-A+ mRNA was isolated with a MagNA pure LC mRNA isolation kit (Roche). One-step real time Q-RT-PCR was carried out with a Hot start LC RNA master SYBR green kit (Roche), using the following primers: Hox-A11, forward 5′-TCTCTAAGGCTCCAGCCTAC-3′, reverse GCTTAACCACGGAGATCTGA; MCK, forward 5′-CACCATGCCGTTCGGCAACA-3′, reverse 5′-GGTTGTCCACCCCAGTCT-3′; 36B4 (housekeeping gene used for RNA normalization), forward 5′-ATGTGCAGCTGATAAAGACTGG-3′, reverse 5′-AGGCCTTGACCTTTTCAGTAAG-3′.
Western blotting and immunofluorescence microscopy. Western blotting and immunostaining were performed using standard procedures. Rabbit anti-MCK was kindly provided by H. Ito, anti-Hox-A11 was a kind gift of L. Patterson. Anti-tubulin, anti-actin, anti-MHC (MY-32) and Cy-3 conjugated anti-mouse IgG were purchased from Sigma, and anti-MyoD antibodies (C20) were purchased from Santa Cruz (Santa Cruz, Calif.).
Efficient uptake of fluorochrome-labelled miRCURY™ knockdown probes (LNA probes from Exiqon) into human K562 cells is shown in
Knockdown of Drosophila Bantam microRNA in Transgenic HEK293 Cells
Knockdown of dme-bantam microRNA in Drosophila KC167 Cells
Knockdown of dme-bantam miRNA in Drosophila KC167 cells by miRCURY™ antisense is shown in
Other embodiments are in the claims.
This application is a divisional of U.S. application Ser. No. 11/388,079, filed Mar. 23, 2006, which claims benefit of U.S. Provisional Application No. 60/664,566, filed Mar. 23, 2005, each of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60664566 | Mar 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11388079 | Mar 2006 | US |
| Child | 12181208 | US |
