ABSTRACT: We report the result of testing the splicing potential of random human genomic sequences. We used randomly fragmented HEK293 DNA in a splicing reporter assay to survey the genome for genomic sequences capable of splicing autonomously as a typical internal exon. From ~10 billion sequenced reads we obtained millions of sequences in the human genome capable of splicing autonomously. A read threshold of 100 yields ~1.25 million exons while also capturing most human mRNA exons.
Project description:22 Normal adult mouse tissues on custom alternative transcript sensitive Affymetrix microarray used to address differeneces in tissue specific alternative splicing. Abstract: Alternative splicing contributes to both gene regulation and protein diversity. To discover broad relationships between regulation of alternative splicing and sequence conservation, we applied a systems approach, using oligonucleotide microarrays designed to capture splicing information across the mouse genome. In a set of 22 adult tissues, we observe expression of RNA containing at least two alternative splice junctions for about a third of the 3200 alternative events we could detect. Statistical comparisons identify 171 cassette exons whose inclusion or skipping is different in brain relative to other tissues, and another 28 exons whose splicing is different in muscle. A subset of these exons is associated with unusual blocks of intron sequence whose conservation in vertebrates rivals that of protein-coding exons. By focusing on sets of exons with similar regulatory patterns, we have identified new sequence motifs implicated in brain and muscle splicing regulation. Of note is a motif strikingly similar to the branchpoint consensus, but which is located downstream of the 5' splice site of exons included in muscle. Analysis of three paralogous membrane-associated guanylate kinase (MAGUK) genes reveals that each contains a paralogous tissue regulated exon with a similar tissue inclusion pattern. While the intron sequences flanking these exons remain highly conserved among mammalian orthologs, the paralogous flanking intron sequences have diverged considerably, suggesting unusually complex evolution of the regulation of alternative splicing in multigene families. Keywords: Alternative splicing isoform specific, adult mouse tissues
Project description:Through splicing analysis of a publicly available RNA-Seq dataset, we discovered TDP-43 represses a cryptic exon splicing event in UNC13A, a gene that had been associated with FTD/ALS through GWA studies. To confirm the sequences of the cryptic exons, we used shRNA to reduce TDP-43 levels in iPSC-derived motor neurons (iPSC-MNs) and by amplicon sequencing the RT-PCR product, we observed the insertion in cells with TDP-43 depletion but not in control shRNA-treated cells. Through sequence alignment, we verified the sequences of the cryptic exons.
Project description:ost characterized tumor antigens are ‘genomic’, i.e. encoded by canonical, non-canonical or somatically mutated genomic sequences. We investigate here the presentation and immunogenicity of tumor antigens derived from non-canonical mRNA splicing events between coding exons and transposable elements (TEs). Comparing non-small cell lung cancer (NSCLC), an immunogenic tumor type, and diverse non-tumor tissues, we identify several thousand splicing junctions between exons and diverse TE classes. A subset of these junctions is both tumor-specific and shared across patients. HLA-I peptidomic identifies peptides encoded by tumor-specific junctions in primary NSCLC samples and lung tumor cell lines. Recurrent junction-encoded peptides are immunogenic in vitro and CD8+ T cells specific for junction-encoded epitopes are present in tumors and tumor-draining lymph nodes from NSCLC patients. We conclude that non-canonical splicing junctions between exons and TEs represent a source of recurrent, immunogenic tumor-specific antigens in NSCLC cancer patients.
Project description:Much remains unknown concerning the mechanism by which the splicing machinery pinpoints short exons within intronic sequences and how splicing factors are directed to their pre-mRNA targets. Part of the explanation probably lies in differences in chromatin organization between exons and introns. Proteomic, co-immunoprecipitation, and sedimentation analyses described here indicated that SF3B1, an essential splicing component of the U2 snRNP complex, is strongly associated with nucleosomes. ChIP-seq and RNA-seq analyses revealed that SF3B1 is specifically bound to nucleosomes located at exonic positions. SF3B1 binding is enriched at nucleosomes positioned over short exons flanked by long introns that are also characterized by differential GC content between exons and introns. Disruption of SF3B1 binding to such nucleosomes affected the splicing of these exons similarly to inhibition of SF3B1 expression. Our findings suggest that the association of SF3B1 with nucleosomes is functionally important for splice site recognition and that SF3B1 conveys splicing-relevant information embedded in chromatin structure.
Project description:Alternative splicing (AS) influences the expression of human genes in diverse ways. We previously used subcellular fraction-sequencing (Frac-Seq) to reveal an unexpected connection between alternative splicing and isoform-specific mRNA translation. Here we apply comparative transcriptomics to explore alternative splicing coupled translational control (AS-TC) across 13 million years of primate evolution. We used Frac-seq to identify polyribosome associated mRNA isoforms from human, chimpanzee and orangutan induced pluripotent stem cell lines. We discovered orthologous AS-TC events with either conserved or species-specific translation patterns. Exons sequences associated with similar sedimentation profiles between species show strong sequence conservation compared to orthologous exons with divergent sedimentation profiles, suggesting exonic cis-regulatory elements influence to translational control. To test this hypothesis we created luciferase reporters from orthologous exons with divergent sedimentation profiles differing by a single nucleotide. Remarkably, single nucleotide substitutions were sufficient to drive species-specific expression of luciferase reporters. Together these data establish that cis-acting elements regulate AS-TC across primate species.
Project description:Co-transcriptional splicing of introns is a defining feature of eukaryotic gene expression. We show that the mammalian spliceosome specifically associates with the S5P CTD isoform of RNA polymerase II (Pol II) as it elongates across spliced exons of protein coding genes, both in human Hela and murine lymphoid cell lines. Immuno-precipitation of MNase digested chromatin with phospho CTD specific antibodies reveals that components of the active spliceosome (both snRNA and proteins) form a specific complex with S5P CTD Pol II. Furthermore a dominant splicing intermediate formed by cleavage at intron 5’ss results in the tethering of upstream exons to this complex at all spliced exons. These are invariably connected to upstream spliced constitutive and less frequently to alternative exons. Finally S5P CTD Pol II accumulates over spliced exons but not adjacent introns. We propose that mammalian splicing employs a rapid, co-transcriptional splicing mechanism based on CTD phosphorylation transitions.
Project description:Efficient targeted control of exon splicing is a major goal of functional genomic and therapeutic applications. Guide RNA-directed, deactivated (d)Cas CRISPR enzymes fused to splicing effectors represent a promising strategy due to the flexibility and presumed specificity of these systems. However, efficient, selective, and generalizable activation of targeted endogenous exons using this approach has not been reported. Here, we identify dCasRx-RBM25 as a potent activator of exons by screening over 300 dCasRx splicing factor fusions tethered to splicing reporters. dCasRx-RBM25 also strongly activates splicing of endogenous alternative exons, when recruited to downstream intron sequences using single guide RNAs. In transcriptome wide analyses we observe a high degree of specificity of dCasRx-RBM25 for endogenous exon targeting. We further leverage the guide array-processing activity of dCasRx to simultaneously target multiple endogenous exons for activation and repression by dCasRx-RBM25. Our results pave the way for versatile exon-resolution functional assays and splicing-directed therapeutic applications.
Project description:Much remains unknown concerning the mechanism by which the splicing machinery pinpoints short exons within intronic sequences and how splicing factors are directed to their pre-mRNA targets. Part of the explanation probably lies in differences in chromatin organization between exons and introns. Proteomic, co-immunoprecipitation, and sedimentation analyses described here indicated that SF3B1, an essential splicing component of the U2 snRNP complex, is strongly associated with nucleosomes. ChIP-seq and RNA-seq analyses revealed that SF3B1 is specifically bound to nucleosomes located at exonic positions. SF3B1 binding is enriched at nucleosomes positioned over short exons flanked by long introns that are also characterized by differential GC content between exons and introns. Disruption of SF3B1 binding to such nucleosomes affected the splicing of these exons similarly to inhibition of SF3B1 expression. Our findings suggest that the association of SF3B1 with nucleosomes is functionally important for splice site recognition and that SF3B1 conveys splicing-relevant information embedded in chromatin structure. MNase-seq on Input and SF3B1 pull-down, mRNA-seq on control and SF3B1 si-RNA treated cells as well as on TSA (Trichostatin A) treated and untreated cells.
Project description:PacBio sequencing was performed to identify alternative splice patterns of Cp/Wp-driven transcripts. We were particularly interested in splicing from Cp/Wp exons to the HF exon. The HF exon contains pri-miR-BHRF1-2 and 1-3, so splicing to the HF exon would indicate that these pri-miRNAs are capable of regulating the 5' EBNA-LP ORF in cis through excision by Drosha.
Project description:Integrating transcriptomic analyses of both clinical PDAC and PDAC models, we identified that the most common neomorphic TP53 mutation (p53R175H) rewires RNA splicing promoting transcriptome-wide retention of cassette exons bearing cytosine(C)-rich sequences.