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Importance of being non-triplet in alternative splicing

ABSTRACT: Alternative mRNA splicing can be used by a cell to regulate gene expression and to generate transcriptomic diversity. Most cases of alternative splicing studied to date are triplet in nature, meaning that both isoforms retain the same translational reading frame. Indeed, non-triplet alternative splicing is sometimes considered evidence of splicing errors or splicing noise. Nevertheless, some examples of functionally important non-triplet alternative splicing exist. We set out to determine the global prevalence, regulation, and function of non-triplet alternative splicing in vivo in C. elegans. We performed RNA-Seq on NMD-deficient mutants and bioinformatically categorized the molecular consequences of non-triplet alternative splicing into three categories: NMD-sensitive isoforms, alternative C-terminal length isoforms, and dual-coding isoforms. We identify hundreds of non-triplet alternative splicing events across these three categories. Genetic and molecular analysis reveals cases of developmental regulation, splicing factor autoregulation, cell-specific splicing patterns, and multiple non-triplet alternative splicing events with physiologically important functions. Together these experiments reveal the importance of non-triplet alternative splicing, a large but underappreciated class of alternative splicing events, for regulating gene expression and generating protein-coding diversity

ORGANISM(S): Caenorhabditis elegans

PROVIDER: GSE313026 | GEO | 2025/12/16

REPOSITORIES: GEO

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Importance of being non-triplet in alternative splicing

Project description:Importance of being non-triplet in alternative splicing

| PRJNA1378137 | ENA

Deep sequencing of pre-translational mRNPs reveals hidden flux through evolutionarily conserved AS-NMD pathways

Project description:Background: Alternative splicing (AS), which generates multiple mRNA isoforms from single genes, is crucial for the regulation of eukaryotic gene expression. The flux through competing AS pathways cannot be determined by traditional RNA-Seq, however, because different mRNA isoforms can have widely differing decay rates. Indeed, some mRNA isoforms with extremely short half-lives, such as those subject to translation-dependent nonsense-mediated decay (AS-NMD), may be completely overlooked in even the most extensive RNA-Seq analyses. Results: RNA immunoprecipitation in tandem (RIPiT) of exon junction complex (EJC) components allows for purification of post-splicing mRNA-protein particles (mRNPs) not yet subject to translation (pre-translational mRNPs) and, therefore, translation-dependent mRNA decay. Here we compared EJC RIPiT-Seq to whole cell RNA-Seq data from HEK293 cells. Consistent with expectation, the flux through known AS-NMD pathways is substantially higher than that captured by RNA-Seq. Our EJC RIPiT-Seq also definitively demonstrates that the splicing machinery itself has no ability to detect reading frame. We identified thousands of previously unannotated splicing events; while many can be attributed to “splicing noise”, others are evolutionarily-conserved events that produce new AS-NMD isoforms likely involved in maintenance of protein homeostasis. Several of these occur in genes whose overexpression has been linked to poor cancer prognosis. Conclusions: Deep sequencing of RNAs in post-splicing, pre-translational mRNPs provides a means to identify and quantify splicing events without the confounding influence of differential mRNA decay. For many known AS-NMD targets, the NMD-linked AS pathway predominates. EJC RIPiT-Seq also enabled identification of numerous conserved but previously unknown AS-NMD events.

2021-02-19 | GSE150228 | GEO

Nanopore sequencing reveals endogenous NMD-targeted isoforms in human cells

Project description:Nonsense-mediated mRNA decay (NMD) is a eukaryotic, translation-dependent degradation pathway that targets mRNAs with premature termination codons and also regulates the expression of some mRNAs that encode full-length proteins. Although many genes express NMD-sensitive transcripts, identifying them based on short-read sequencing data remains a challenge. To identify and analyze endogenous targets of NMD, we applied cDNA Nanopore sequencing and short-read sequencing to human cells with varying expression levels of NMD factors. Our approach detects full-length NMD substrates that are highly unstable and increase in levels or even only appear when NMD is inhibited. Among the many new NMD-targeted isoforms that our analysis identified, most derive from alternative exon usage. The isoform-aware analysis revealed many genes with significant changes in splicing but no significant changes in overall expression levels upon NMD knockdown. NMD-sensitive mRNAs have more exons in the 3΄UTR and for mRNAs with a termination codon in the last exon. The length of the 3΄UTR per se does not correlate with NMD sensitivity. Analysis of splicing signals reveals isoforms where NMD has been co-opted in the regulation of gene expression, but a main function is most likely to rid the transcriptome of isoforms resulting from spurious splicing events. Long-read sequencing enabled the identification of many novel NMD-sensitive mRNAs and revealed both known and unexpected features concerning their biogenesis and their biological role. Our data provide a highly valuable resource of human NMD transcript targets for future genomic and transcriptomic applications.

2021-07-20 | E-MTAB-10452 | 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

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

Regulation of alternative splicing by the core spliceosomal machinery

Project description:Abstract: Alternative splicing (AS) plays a major role in the generation of proteomic diversity and in gene regulation. However, the role of the basal splicing machinery in regulating AS remains poorly understood. Here we show that the core snRNP protein SmB/B’ self-regulates its expression by promoting the inclusion of a highly-conserved alternative exon in its own pre-mRNA that targets the spliced transcript for nonsense-mediated mRNA decay (NMD). Depletion of SmB/B’ in human cells results in reduced levels of snRNPs and in a striking reduction in the inclusion levels of hundreds of alternative exons, with comparatively few effects on constitutive exon splicing levels. The affected alternative exons are enriched in genes encoding RNA processing and other RNA binding factors, and a subset of these exons also regulate gene expression by activating NMD. Our results thus demonstrate a role for the core spliceosomal machinery in controlling an exon network that appears to modulate the levels of many RNA processing factors. HeLa cells were transfected with a control non-targeting siRNA pool (siNT), or with siRNA pools designed to knockdown SmB/B' or SRSF1 (also known as SF2/ASF/SFRS1). Sequence reads were aligned to exon-exon junction sequences in a database of EST/cDNA-mined cassette-type alternative splicing events. Processed data files (.bed and .txt) provided as supplementary files on the Series record. Processed data file build information: hg18.

2011-02-01 | E-GEOD-26463 | biostudies-arrayexpress

Transposable element exonization by non-canonical splicing generates a diversity reservoir of functional protein isoforms

Project description:mRNA splicing enlarges the diversity of the protein repertoire, mainly through alternative exon retention or skipping. Although non-canonical splicing variants that exonize intronic regions were recently identified at the mRNA level, their contribution to the cellular proteome remains unclear. Here, we describe a population of 1300 unannotated protein isoforms generated by non-canonical splicing between exons and transposable elements (TE) using a combination of transcriptome assembly, ribosome profiling, and mass spectrometry. Despite being shorter and expressed at lower levels, their translation efficiency is similar to that of canonical isoforms, and they are shared between individuals. Functional analyses of 5 different non-canonical isoforms show stable expression, specific intracellular localization, and modified functions, as compared to the corresponding canonical isoforms. Non-canonical isoforms derive mainly from evolutionarily ancient genes and are a preferential source of alternative splicing upon which natural selection can act. We conclude that recently exonized TE isoforms are potentially functional and represent a diversity reservoir of novel protein isoforms.

2024-12-12 | GSE234223 | GEO

Cryptic splicing mediates genetic and therapeutic perturbation of human gene expression levels [naRNA_LCLs]

Project description:Alternative splicing (AS) in human genes is widely viewed as a mechanism for enhancing proteomic diversity. AS can also impact gene expression levels without increasing protein diversity by producing “unproductive” transcripts that are targeted for rapid degradation by nonsense-mediated decay (NMD). However, the relative importance of this regulatory mechanism remains underexplored. To better understand the impact of AS-NMD relative to other regulatory mechanisms, we analyzed population-scale genomic data across eight molecular assays, covering various stages from transcription to cytoplasmic decay. We report threefold more unproductive splicing compared to prior estimates using steady-state RNA. This unproductive splicing compounds across multi-intronic genes, resulting in 15% of all transcript molecules from protein-coding genes being unproductive. Leveraging genetic variation across cell lines, we find that GWAS trait-associated loci explained by AS are as often associated with NMD-induced expression level differences as with differences in protein isoform usage. Employing the splice-switching drug risdiplam to manipulate AS at hundreds of genes, we find that ~3/4 of drug-induced isoforms are targeted by NMD, suggesting that most aberrant splicing influences expression levels. Our findings suggest much of the impact of AS is mediated by NMD-induced changes in gene expression rather than diversification of the proteome.

2024-05-10 | GSE252005 | GEO

Cryptic splicing mediates genetic and therapeutic perturbation of human gene expression levels [Cut&Tag]

2024-05-10 | GSE252003 | GEO

Differentially expressed genes and transcript isoforms in mouse NSCs expressing miR-128

Project description:We identify a brain-specific microRNA—miR-128—that represses Nonsense Mediated mRNA Decay (NMD) and thereby controls batteries of transcripts in neural cells. miR-128 represses NMD by targeting the RNA helicase UPF1 and the exon-junction complex core component MLN51. We employed exon arrays for this analysis, as this platform detects expression levels of individual exons and thus allows detection of not only differentially expressed transcripts (DETs), but also alternative isoform transcripts (AITs). The latter is particularly relevant to our study because alternative RNA processing events (e.g., RNA splicing, alternative promoter usage, and alternative polyadenylation-site usage) often place a translation termination codon in a premature context and thereby trigger NMD. Compare different expressed genes and transcript isoforms in mouse NSCs miR-128 positive vs miR-128 negative (Control). Mouse NSCs, that do not normally express miR-128, were nucleofected with either miR-128 (biological triplicates were analysed) or miR-Control (biological triplicates). RNA was extracted 72hrs later, and Exon Array was performed to identify target genes.

2011-04-28 | E-GEOD-28889 | biostudies-arrayexpress

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