Project description:Recurrent mutations in the spliceosome are observed in several human cancers but their functional and therapeutic significance remain elusive. SF3B1, the most frequently mutated component of the spliceosome in cancer, is involved in the recognition of the branch point sequence (BPS) during selection of the 3’ splice site (ss) in RNA splicing. Here, we report that common and tumor-specific splicing aberrations are induced by SF3B1 mutations and establish aberrant 3’ ss selection as the most frequent splicing defect. Strikingly, mutant SF3B1 utilizes a BPS that differs from that used by wild-type SF3B1 and requires the canonical 3’ ss to enable aberrant splicing during the second step. Approximately 50% of the aberrantly spliced mRNAs are subjected to nonsense-mediated decay resulting in downregulation of gene and protein expression. These findings ascribe functional significance to the consequences of SF3B1 mutations in cancer. 72 samples, including two sets of patient data and cell lines with two additional technical replicates each
Project description:Most eukaryotes harbor two distinct pre-mRNA splicing machineries: the major spliceosome, which removes >99% of introns, and the minor spliceosome, which removes rare, evolutionarily conserved introns. Although hypothesized to serve important regulatory functions, physiologic roles for the minor spliceosome are not well understood. For example, the minor spliceosome component ZRSR2 is subject to recurrent, leukemia-associated mutations, yet functional connections between minor introns, hematopoiesis, and cancers are unclear. Here, we identify that impaired minor intron excision via ZRSR2 loss enhances hematopoietic stem cell self-renewal. CRISPR screens mimicking nonsense-mediated decay of minor intron-containing mRNAs converged on LZTR1, a regulator of Ras-related GTPases. LZTR1 minor intron retention was also discovered in the RASopathy Noonan syndrome, due to intronic mutations disrupting splicing, and diverse solid tumors. These data uncover minor intron recognition as a regulator of hematopoiesis, noncoding mutations within minor introns as cancer drivers, and links between ZRSR2 mutations, LZTR1 regulation, and leukemias.
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
Project description:Recurrent mutations in the spliceosome are observed in several human cancers but their functional and therapeutic significance remain elusive. SF3B1, the most frequently mutated component of the spliceosome in cancer, is involved in the recognition of the branch point sequence (BPS) during selection of the 3’ splice site (ss) in RNA splicing. Here, we report that common and tumor-specific splicing aberrations are induced by SF3B1 mutations and establish aberrant 3’ ss selection as the most frequent splicing defect. Strikingly, mutant SF3B1 utilizes a BPS that differs from that used by wild-type SF3B1 and requires the canonical 3’ ss to enable aberrant splicing during the second step. Approximately 50% of the aberrantly spliced mRNAs are subjected to nonsense-mediated decay resulting in downregulation of gene and protein expression. These findings ascribe functional significance to the consequences of SF3B1 mutations in cancer.
Project description:The spliceosome, a complex of RNA and proteins, is indispensable for orchestrating splicing events critical to mRNA maturation. Mutations in spliceosome components are linked to tissue-specific diseases known as spliceosomopathies. Among the diverse splicing events mediated by the spliceosome, intron retention (IR) has been extensively studied in plants and fungi. However, its functional significance in mammals has only recently gained attention. IR is recognized for its role in the differentiation of neuronal and hematopoietic cells. This study leverages RNA sequencing to explore IR events during osteogenic differentiation in ST2 cells. Genome-wide analysis revealed a significant increase in IR during differentiation, affecting clusters of genes involved in RNA processing. The identification of premature termination codons (PTCs) within intron-retaining transcripts indicates that IR may regulate RNA processing gene expression through nonsense-mediated decay (NMD). Additionally, inhibition of NMD caused accumulation of these mRNA transcripts and disrupted osteogenic differentiation. We propose that IR triggers NMD to enhance mRNA decay in a fraction of splicing genes, leading to spliceosome reprogramming to facilitate osteogenic differentiation.
Project description:The role of many splicing factors in pre-mRNA splicing and the involvement of these factors in the processing of specific transcripts have often been defined through the analysis of loss of function mutants in vivo. Here we show that inactivating the nonsense mediated mRNA decay (NMD) results in an enhancement of splicing phenotypes associated with several splicing factors mutations. Tiling microarrays showed that inactivation of the NMD factor Upf1p in the prp17Î and prp18Î mutant strains reveals a larger spectrum of splicing defects than what is observed in the single mutants, including new transcripts previously shown unaffected by Prp17p or Prp18p inactivation. In addition, inactivation of Upf1 in the prp22-1 mutant enhances the unspliced precursor accumulation phenotype of several specific transcripts and partially suppresses growth defects associated with the prp17Î or prp22-1 mutations. These results support the idea that RNA surveillance by NMD mutes some of the effects of splicing factors mutations and show that the roles of splicing factors and their transcripts specificity cannot be fully understood in vivo unless RNA degradation systems that degrade unspliced precursors are also inactivated. Three samples from the Prp17delta, Prp18delta, Prp17deltaUpf1delta and Prp18Upf1delta mutants were grown indepedently and analyzed by tiling arrays to understand the role of the NMD component Upf1 in minimizing the accumulation of unspliced RNAs generated by the Prp17delta and Prp18delta splicing mutations.
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.