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Genome-wide discovery of human splicing branchpoints [BPCapture]

ABSTRACT: Gene splicing requires three basal genetic elements; the 3’ and 5’ splice sites and the branchpoint to which the 5’ intron termini is ligated to form a closed lariat during the splicing reaction. The 5’ and 3’ splice sites that define exon boundaries have been widely identified, revealing pervasive transcription and splicing of human genes. However, the locations of the third requisite element, the branchpoint, are still largely unknown. Here we employ two complementary approaches, targeted RNA sequencing and exoribonuclease digestion, to distil sequenced reads that traverse the lariat junction and, via non-conventional alignment, locate human branchpoint nucleotides. Alignments identify 88,748 branchpoints that correspond to 20% of known introns, with 76% supported by diagnostic sequence mismatch errors. This affords a first genome-wide analysis of branchpoints, describing their distribution, selection, and the existence of a diverse array of overlapping sequence motifs with distinct usage, evolutionary histories, and co-variation with distal splicing elements. The overlap of branchpoints with noncoding human genetic variation also indicates a notable contribution to disease. This annotation and analysis incorporates branchpoints into transcriptomic research and reflects a core role for this element in the regulatory code that governs gene splicing and expression.

ORGANISM(S): Homo sapiens

PROVIDER: GSE53326 | GEO | 2014/10/01

SECONDARY ACCESSION(S): PRJNA231723

REPOSITORIES: GEO

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Genome-wide discovery of human splicing branchpoints [BPCapture]

Project description:Gene splicing requires three basal genetic elements; the 3M-bM-^@M-^Y and 5M-bM-^@M-^Y splice sites and the branchpoint to which the 5M-bM-^@M-^Y intron termini is ligated to form a closed lariat during the splicing reaction. The 5M-bM-^@M-^Y and 3M-bM-^@M-^Y splice sites that define exon boundaries have been widely identified, revealing pervasive transcription and splicing of human genes. However, the locations of the third requisite element, the branchpoint, are still largely unknown. Here we employ two complementary approaches, targeted RNA sequencing and exoribonuclease digestion, to distil sequenced reads that traverse the lariat junction and, via non-conventional alignment, locate human branchpoint nucleotides. Alignments identify 88,748 branchpoints that correspond to 20% of known introns, with 76% supported by diagnostic sequence mismatch errors. This affords a first genome-wide analysis of branchpoints, describing their distribution, selection, and the existence of a diverse array of overlapping sequence motifs with distinct usage, evolutionary histories, and co-variation with distal splicing elements. The overlap of branchpoints with noncoding human genetic variation also indicates a notable contribution to disease. This annotation and analysis incorporates branchpoints into transcriptomic research and reflects a core role for this element in the regulatory code that governs gene splicing and expression. CaptureSeq identification of branchpoint nucleotides

2014-10-01 | E-GEOD-53326 | biostudies-arrayexpress

Genome-wide discovery of human splicing branchpoints [RNAse]

2014-10-01 | E-GEOD-53327 | biostudies-arrayexpress

Genome-wide discovery of human splicing branchpoints [RNAse]

Project description:Gene splicing requires three basal genetic elements; the 3’ and 5’ splice sites and the branchpoint to which the 5’ intron termini is ligated to form a closed lariat during the splicing reaction. The 5’ and 3’ splice sites that define exon boundaries have been widely identified, revealing pervasive transcription and splicing of human genes. However, the locations of the third requisite element, the branchpoint, are still largely unknown. Here we employ two complementary approaches, targeted RNA sequencing and exoribonuclease digestion, to distil sequenced reads that traverse the lariat junction and, via non-conventional alignment, locate human branchpoint nucleotides. Alignments identify 88,748 branchpoints that correspond to 20% of known introns, with 76% supported by diagnostic sequence mismatch errors. This affords a first genome-wide analysis of branchpoints, describing their distribution, selection, and the existence of a diverse array of overlapping sequence motifs with distinct usage, evolutionary histories, and co-variation with distal splicing elements. The overlap of branchpoints with noncoding human genetic variation also indicates a notable contribution to disease. This annotation and analysis incorporates branchpoints into transcriptomic research and reflects a core role for this element in the regulatory code that governs gene splicing and expression.

2014-10-01 | GSE53327 | GEO

A comprehensive map of intron branchpoints and lariat RNAs in plants

Project description:Lariat is formed by excised intron, in which the 5' splice site joints with the branchpoint (BP) during splicing. Although lariat RNAs are usually degraded by DBR1 (RNA debranching enzyme 1), recent findings in animals showed that many lariat RNAs were widely detected under physiological conditions. In contrast, the features of BPs and to what extent lariat RNAs accumulate naturally are largely unexplored in plants. Here, we analyzed 948 RNA sequencing datasets to document plant BPs and lariat RNAs on a genome-wide scale. In total, we identified 13872, 5199, 29582, and 13478 BPs in Arabidopsis, tomato, rice, and maize, respectively. Features of plant BPs are highly similar to those in yeast and human, in that BPs are adenine-preferred and flanked by uracil-enriched sequences. Intriguingly, ~20% of introns harbor multiple BPs, and BP usage is tissue-specific. Furthermore, 10580 lariat RNAs accumulate in wild type Arabidopsis plants, and most of these lariat RNAs originate from longer or retroelement-depleted introns, and the expression of these lariat RNAs significantly correlated with the incidence of back-splicing of parent exons. Collectively, our results provide the first comprehensive map of intron BPs and lariat RNAs in plants, and uncover a novel link between lariat turnover and splicing.

2019-04-17 | GSE117416 | GEO

The Debranching Enzyme Dbr1 Regulates Lariat Turnover and Intron Splicing

Project description:The majority of genic transcription is intronic. Introns are removed by splicing as branched lariat RNAs which require rapid recycling. The branch site is recognized during splicing catalysis and later debranched by Dbr1 in the rate-limiting step of lariat turnover. Through generation of the first viable DBR1 knockout cell line, we find the predominantly nuclear Dbr1 enzyme to encode the sole debranching activity in human cells. Dbr1 preferentially debranches substrates that contain canonical U2 binding motifs, suggesting that branchsites discovered through sequencing do not necessarily represent those favored by the spliceosome. We find that Dbr1 also exhibits specificity for particular 5' splice site sequences. We identify Dbr1 interactors through co-immunoprecipitation mass spectroscopy. We present a mechanistic model for Dbr1 recruitment to the branchpoint through the intron-binding protein AQR. In addition to a 20-fold increase in lariats, Dbr1 depletion increases exon skipping. Using ADAR fusions to timestamp lariats, we demonstrate a defect in spliceosome recycling. In the absence of Dbr1, spliceosomal components remain associated with the lariat for a longer period of time. As splicing is co-transcriptional, slower recycling increases the likelihood that downstream exons will be available for exon skipping.

2023-06-26 | MSV000092263 | MassIVE

Profiling lariat intermediates reveals genetic determinants of early and late co-transcriptional splicing

Project description:Long introns with short exons in vertebrate genes are thought to require spliceosome assembly across exons (exon definition), rather than introns, thereby requiring transcription of an exon to splice an upstream intron. Here, we developed CoLa-seq (co-transcriptional lariat sequencing) to investigate the timing and determinants of co-transcriptional splicing genome wide. Unexpectedly, 90% of all introns, including long introns, can splice before transcription of a downstream exon, indicating that exon definition is not obligatory for most human introns. Still, splicing timing varies dramatically across introns, and various genetic elements determine this variation. Strong U2AF2 binding to the polypyrimidine tract predicts early splicing, explaining exon definition-independent splicing. Together, our findings question the essentiality of exon definition and reveal features beyond intron and exon length that are determinative for splicing timing.

2022-11-26 | GSE204834 | GEO

mRNA profiling of wildtype, germline depleted, NMD mutant C. elegans whole worms and wildtype dissected gonads

Project description:Adjacent alternative 3’ splice sites, those separated by ≤18nt, provide a unique problem in the study of alternative splicing regulation; there is overlap of the cis-elements that define the adjacent sites. Identification of the intron's 3' end depends upon sequence elements that define the branchpoint, polypyrimidine tract and terminal AG dinucleotide. Starting with RNA-seq data from germline-enriched and somatic cell-enriched C. elegans samples, we identify hundreds of introns with adjacent alternative 3’ splice sites. We identify 203 events that undergo tissue-specific alternative splicing. For these, the regulation is mono-directional, with somatic cells preferring to splice at the distal 3' splice site and germline cells showing a distinct shift towards usage of the adjacent proximal 3' splice site. Splicing patterns in somatic cells follow consensus rules of 3’ splice site definition, using sites with a short stretch of pyrimidines and an AG dinucleotide. Splicing in germline cells occurs at proximal 3' splice sites that frequently lack a polypyrimidine tract or, occasionally, the AG dinucleotide. We provide evidence that use of germline-specific proximal 3' splice sites is conserved across Caenorhabditis species. We propose that divergent mechanisms exist between germline and somatic cells in determining an intron terminus at adjacent alternative 3’ splice sites. Examination of alternative splicing changes between germline- and somatic-cell enriched samples as well as nonsense-mediated decay mutants.

2015-04-22 | E-GEOD-64672 | biostudies-arrayexpress

Widespread Use of Non-Productive Alternative Splice Sites in Saccharomyces cerevisiae

Project description:Using RNA-Seq analysis of nonsense-mediated mRNA decay (NMD) mutant strains, we show that many Saccharomyces cerevisiae intron-containing genes exhibit usage of alternative splice sites, but most transcripts generated by splicing from these sites are non-functional because they introduce premature termination codons leading to transcript degradation by NMD. Analysis of splicing mutants combined with NMD inactivation revealed the role of specific splicing factors in governing the use of these alternative splice sites and identified novel functions for Prp17p in enhancing the use of branchpoint-proximal upstream 3M-bM-^@M-^Y splice sites and for Prp18p in suppressing the usage of a non-canonical AUG 3M-bM-^@M-^Y-splice site. The use of non-productive alternative splice sites can limit the expression of some transcripts and can be increased in stress conditions in a promoter-dependent manner, contributing to the down-regulation of genes during stress. These results reveal that alternative splicing is frequent in S.cerevisiae but masked by RNA degradation and that the use of alternative splice sites is mostly aimed at controlling transcript levels rather than increasing proteome diversity. mRNA-Seq profiling of 3 mutants in the nonsense-mediated mRNA decay pathway and wildtype yeast

2014-02-21 | E-GEOD-55213 | biostudies-arrayexpress

Mutant SF3B1 promotes AKT and NF-kB driven mammary tumorigenesis

Project description:Mutations in the core RNA splicing factor SF3B1 are prevalent in leukemias and uveal melanoma, but also recurrent in epithelial malignancies such as breast cancer. Whereas hotspot mutations in SF3B1 alter hematopoietic differentiation, whether SF3B1 mutations contribute to epithelial cancer development and progression is unknown. Here, we identify that SF3B1 mutations in mammary epithelial and breast cancer cells induce a recurrent pattern of aberrant splicing leading to activation of AKT and NF-kB, enhanced cell migration, and accelerated tumorigenesis. Transcriptomic analysis of human cancer specimens, MMTV-cre Sf3b1K700E/WT mice, and isogenic mutant cell lines identified hundreds of aberrant 3’ splice sites induced by mutant SF3B1, a portion of which were breast-specific. Across mouse and human tumors, mutant SF3B1 promoted aberrant splicing (dependent on aberrant branchpoints as well as pyrimidines downstream of the aberrant branchpoint) and consequent suppression of PPP2R5A and MAP3K7, critical negative regulators of AKT and NF-kB. Coordinate activation of NF-kB and AKT signaling was observed in the knock-in models, leading to accelerated cell migration and tumor development in combination with mutant PIK3CA but also hypersensitizing cells to AKT kinase inhibitors. These data identify mutations in SF3B1 as drivers of breast tumorigenesis and reveal unique vulnerabilities in cancers harboring them.

2021-01-05 | GSE145471 | GEO

Widespread Use of Non-Productive Alternative Splice Sites in Saccharomyces cerevisiae

Project description:Using RNA-Seq analysis of nonsense-mediated mRNA decay (NMD) mutant strains, we show that many Saccharomyces cerevisiae intron-containing genes exhibit usage of alternative splice sites, but most transcripts generated by splicing from these sites are non-functional because they introduce premature termination codons leading to transcript degradation by NMD. Analysis of splicing mutants combined with NMD inactivation revealed the role of specific splicing factors in governing the use of these alternative splice sites and identified novel functions for Prp17p in enhancing the use of branchpoint-proximal upstream 3’ splice sites and for Prp18p in suppressing the usage of a non-canonical AUG 3’-splice site. The use of non-productive alternative splice sites can limit the expression of some transcripts and can be increased in stress conditions in a promoter-dependent manner, contributing to the down-regulation of genes during stress. These results reveal that alternative splicing is frequent in S.cerevisiae but masked by RNA degradation and that the use of alternative splice sites is mostly aimed at controlling transcript levels rather than increasing proteome diversity.

2014-02-21 | GSE55213 | GEO

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