ABSTRACT: Analysis of splicing defects in Schizosaccharomyces pombe upon chemical genetic inhibition of splicing kinases dsk1, lkh1, and prp4, as well as alanine-mutation of phosphorylated residues in the splicing factors bpb1, prp2, rsd1, srp1, srp2, usp101, usp103, sum3, prp22, cdc5, and cwf22. This study shows the splicing kinase dsk1 modulates splicing efficiency of introns with non-consensus splice sites, likely through phosphorylation of bpb1. Modulation of splicing efficiency of transcripts through kinase signaling pathways may afford the necessary flexibility to tune the gene expression profile in response to environmental and developmental cues. Experiments were conducted as direct two-color designs with 2-3 biological replicates per genotype pairing. Raw microarray data was normalized with loess normalization using the R package limma. Log2-fold changes (perturbation over reference) are reported. Each splicing event on the custom-designed splicing microarray was monitored with an exon probe reading out mRNA changes, an intron probe for unspliced pre-mRNA, and a splice junction probe spanning the junction between two spliced exons. For the analysis of the splicing efficiency for a given intron, a score was calculated as exon*intron/junction.
Project description:General discard pathways eliminate unprocessed and irregular pre-mRNAs to control the quality of gene expression. In contrast to such general pre-mRNA decay, we describe here a nuclear pre-mRNA degradation pathway that controls the expression of select intron-containing genes. We show that the fission yeast nuclear poly(A)-binding protein, Pab2, and the nuclear exosome subunit, Rrp6, are the main factors involved in this polyadenylation-dependent pre-mRNA degradation pathway. Transcriptome analysis and intron swapping experiments revealed that inefficient splicing is important to dictate susceptibility to Pab2-dependent pre-mRNA decay. We also show that negative splicing regulation can promote the poor splicing efficiency required for this pre-mRNA decay pathway, and in doing so identify a mechanism of cross-regulation between paralogous ribosomal proteins through nuclear pre-mRNA decay. Our findings unveil a layer of regulation in the nucleus in which the turnover of specific pre-mRNAs, besides the turnover of mature mRNAs, is used to control gene expression.
Project description:Alternative pre-mRNA splicing is a prevalent mechanism in mammals that promotes proteomic diversity, including expression of cell-type specific protein isoforms. We characterized a role for RBM38 (RNPC1) in regulation of alternative splicing during late erythroid differentiation. We used an affymetrix human exon junction (HJAY) splicing microarray to identify a panel of RBM38-regulated alternatively spliced transcripts. Using microarray databases, we noted high RBM38 expression levels in CD71+ erythroid cells and thus chose to examine RBM38 expression during erythroid differentiation of human hematopoietic stem cells, detecting enhanced RBM38 expression during late erythroid differentiation. In differentiated erythroid cells, we validated a subset of RBM38-regulated splicing events and determined that RBM38 regulates activation of Protein 4.1R (EPB41) exon 16 during late erythroid differentiation. Using Epb41 minigenes, Rbm38 was found to be a robust activator of exon 16 splicing. To further address the mechanism of RBM38-regulated alternative splicing, a novel mammalian protein expression system, followed by SELEX-Seq, was used to identify a GU-rich RBM38 binding motif. Lastly, using a tethering assay, we determined that RBM38 can directly activate splicing when recruited to a downstream intron. Together, our data support the role of RBM38 in regulating alternative splicing during erythroid differentiation. siRNA knockdown of RBM38 was perfomed in human MCF-7 breast cancer cells. The efficiency of RBM38 knockdown was monitored by western blot using an RBM38 antibody (Santa Cruz Biotechnology, SC-85873). We conducted HJAY exon and exon junction array profiling on RNAs from four siRBM38 treated MCF-7 samples vs. four sicontrol treated MCF-7 samples Control / knockdown comparison.
Project description:Alternative splicing generates functional diversity in higher organisms through alternative first and last exons, skipped and included exons, intron retentions and alternative donor and acceptor sites. In large-scale microarray studies in human and mouse, emphasis so far has been placed on exon-skip events, leaving the prevalence and importance of other splice types largely unexplored. Using a new human splice variant database and a genome-wide microarray to probes thousands of splice events of each type, we measured differential expression of splice types across 6 pairs of diverse cell lines and validated the database annotation process. Results suggest that splicing in human is more complex than simple exon skip events, which account for a minority of splicing differences. The relative frequency of differential expression of the splice types correlates with what is found by our annotation efforts. In conclusion, alternative splicing in human cells is considerably more complex than the canonical example of the exon-skip. The complementary approaches of genome-wide annotation of alternative splicing in human and design of genome-wide splicing microarrays to measure differential splicing in biological samples provide a powerful high-throughput tool to study the role of alternative splicing in human biology. Keywords: alternative splicing Overall design: Identification of alternative splicing changes in pairwise sample comparisons with technical replicates as control. Array Design: The annotated database of human splice isoforms, SpliceExpress Human Spliceome 1 (SEHS1), was created by combining RefSeq, Build 35 of the NCBI genome assembly and Unigene-derived EST alignments from Alternative Splicing Database (ASD). For each gene, exonic regions and exonic portions from 5' to 3' were indexed. Using the in-dexes as well as sequence coordinates, a splice type was assigned to every splice event as exon-skips/includes, intron retentions, alternative first exons, alternative last exons, alter-native donor sites, and alternative acceptor sites. A second database of alternative splicing in human, SpliceExpress Human Spliceome 2 (SEHS2), was generated independently using UCSC genome assembly hg17 with genomic alignments of 3,493,559 cDNA/ESTs and 24,297 RefSeq mRNAs. Data were filtered to eliminate likely spurious introns of less than 15 bases and remove questionable spliceoforms based on the number of sequences providing evidence and based on donor and acceptor motifs. High-confidence splice events contributed to the microarray platform SEHS1.5. All events in SEHS1.5 were common to both SEHS1 and SEHS2 databases. To avoid mismatched probes arising from low quality EST sequences, the respective genomic sequences were used. To detect alternative splicing events, the probe set included 3 exon-exon junction probes per exon-skip event; two exon-exon junction probes per alternative first or last exon; one exon-exon junction probe plus two exon-intron junction probes per intron retention; and two exon-exon junction probes per alternative donor or acceptor site; and at least one probe per single exon gene or gene without splice isoforms. Probes had an average length of 38 nucleotides. Since fixed-length probes repre-senting junctions may vary widely in GC content and melting temperature, probe lengths were varied from 34 to 42 bases so that the total melting temperature was optimized to 68 degrees. Junction probes were isothermally balanced across the splice junction to mini-mize disparities in melting temperature between the two portions. Sense strand oligonucleotides with an additional 10-base polyT linker at the 3' end as spacer were synthesized in situ by NimbleGen Systems. Samples: Four human cell lines were tested: Capan 1 (pancreas), HEK 293 (Kidney), MCF7A (breast) and CaCO2 (colon) using an expression protocol. Cell lines were obtained from the American Tissue Culture Collection (Manassas, VA) and cultured according to ATCC specifications. Replicate data were generated for each cell line. For HEK293, two additional replicates were generated for use as a control to assign statistical significance when comparing replicate samples.
Project description:The exon junction complex (EJC) is a highly conserved ribonucleoprotein complex which binds RNAs during splicing and remains associated with them following export to the cytoplasm. While the role of this complex in mRNA localization, translation and degradation has been well characterized, its mechanism of action in splicing a subset of Drosophila and human transcripts remains to be elucidated. Here, we describe a novel function for the EJC and its splicing subunit RnpS1 in preventing transposon accumulation in both Drosophila germline and surrounding somatic follicle cells. This function is mediated specifically through the control of piwi transcript splicing, where in the absence of RnpS1 the fourth intron of piwi is retained. Within this intron the polypyrimidine tract is disrupted by a transposon-adjacent A/T-rich sequence that confers dependence on RnpS1. Finally, we demonstrate that RnpS1-dependent removal of this intron requires splicing of the flanking introns, suggesting a model in which the EJC facilitates the splicing of weak introns following its initial deposition at adjacent exon junctions. These data demonstrate a novel role for the EJC in regulating piwi intron excision and provide a mechanism for its function during splicing. Small-RNA libraries from two control samples and four knockdowns in germline or somatic tissues of the Drosophila melanogaster ovary.
Project description:To determine the global impact of the clbn mutation on gene expression and efficiency of U2- and U12-type splicing, we analyzed the transcriptome of 108hpf wt and clbn mutant larvae by microarrays and RNA sequencing. RNAseq data was used to characterize intron retention of U2-type and U12-type intron on a genome-wide scale to confirm that rnpc3 deficiency specifically impairs U12-type splicing. RNAseq and microarray data were combined to yield high-confidence lists of differentially expressed genes which show that impaired U12-type splicing has a wide-ranging effect on the developing transcriptome. RNAseq libraries prepared from 108 hours post-fertilization zebrafish larvae (approx. 60 embryos each, genotyped homozygous wildtype and homozygous clbns841 mutants, respectively)
Project description:The functional consequences for alternative splicing of altering the transcription rate have been the subject of intensive study in mammalian cells but less is known about effects on splicing of changing the transcription rate in yeast. We present several lines of evidence showing that slow RNA polymerase II elongation increases both co-transcriptional splicing and splicing efficiency and faster elongation reduces co transcriptional splicing and splicing efficiency in budding yeast, suggesting that splicing is more efficient when co-transcriptional. Moreover, we demonstrate that altering RNA polymerase II elongation rate in either direction compromises splicing fidelity, and we reveal that splicing fidelity depends largely on intron length together with secondary structure and splice site score. These effects are notably stronger for the highly expressed ribosomal protein coding transcripts. We propose that transcription by RNA polymerase II is tuned to optimise the efficiency and accuracy of ribosomal protein gene expression, while allowing flexibility in splice site choice with the nonribosomal protein transcripts. Overall design: Examination of pre-mRNA splicing in RNAPII elongation mutants. All experiments were performed in duplicate.
Project description:To determine the prevalence of cotranscriptional splicing in Drosophila, we sequenced nascent RNA transcripts from Drosophila S2 cells as well as from Drosophila heads. 87% of introns assayed manifest more than 50% cotranscriptional splicing. The remaining 13% are cotranscriptionally spliced poorly, or slowly, with ~3% being almost completely retained in nascent pre-mRNA. Although individual introns showed slight but statistically significant differences in splicing efficiency, similar global levels of splicing were seen from both sources. Importantly, introns with low cotranscriptional splicing efficiencies are present in the same primary transcript with efficiently spliced introns, indicating that splicing is intron-specific. The analysis also indicates that cotranscriptional splicing is less efficient for first introns, longer introns and introns annotated as alternative. FinallyFinally, S2 cells expressing the slow RpII215C4 mutant manifest substantially less intron retention than wild-type S2 cells. Examination of Total pA and Nascent RNA from 2 different cell populations and isolated fly heads.
Project description:The exon junction complex (EJC) is a highly conserved ribonucleoprotein complex which binds RNAs at a late stage of the splicing reaction and remains associated following export to the cytoplasm. This complex is involved in several cellular post-transcriptional processes including mRNA localization, translation and degradation. The EJC plays an additional role in the splicing of a subset of genes in Drosophila and in human cells but the underlying mechanism remains to be elucidated. Here, we have found a novel function for the EJC and its splicing subunit RnpS1 in preventing transposon accumulation in both Drosophila germline and surrounding follicular cells. This function is mediated specifically through the control of the splicing of the piwi transcript. In absence of RnpS1 one of the piwi intron is retained. This intron contains a weak 5’ splice site as well as degenerate transposon fragments, reminiscent of heterochromatic introns. In addition, we identified a small A/T rich region, which alters its polypyrimidine tract (PPT) and confers the RnpS1’s dependency. Finally, we showed that the removal of this intron by RnpS1 requires the initial splicing of the flanking introns, suggesting a model in which the EJC facilitates the splicing of challenging introns following its initial deposition to adjacent exon junctions. In total there are 4 different conditions. Comparisons were made between piwi mutant vs control piwi and rnps1 KD vs controls RnpS1
Project description:To determine the global impact of the clbn mutation on gene expression and efficiency of U2- and U12-type splicing, we analyzed the transcriptome of 108hpf wt and clbn mutant larvae by microarrays and RNA sequencing. RNAseq data was used to characterize intron retention of U2-type and U12-type intron on a genome-wide scale to confirm that rnpc3 deficiency specifically impairs U12-type splicing. RNAseq and microarray data were combined to yield high-confidence lists of differentially expressed genes which show that impaired U12-type splicing has a wide-ranging effect on the developing transcriptome. Total RNA was prepared from pools consisting of approx. 20 individually genotyped homozygous wildtype or mutant larvae, respectively. Three biologically independent replicate pools were generated and analyzed for each condition.
Project description:During meiosis in yeast, global splicing efficiency increases. The mechanism for this is relief of competition for the splicing machinery by repression of intron-containing ribosomal protein genes (RPGs). Repression of RPGs with rapamycin also increases splicing efficiency in vegetative cells. Reducing levels of an RPG-dedicated transcription factor globally improves splicing and suppresses the temperature-sensitive growth defect of a spliceosome mutation. These results indicate that the spliceosome is limiting and pre-mRNAs compete with each other. Under these conditions, splicing efficiency of a given pre-mRNA therefore depends on both its concentration and affinity for the limiting splicing factor(s) as well as those of the competing pre-mRNAs. We propose that trans-competition control of splicing helps repress meiotic gene expression in vegetative cells, and promotes efficient meiosis. Competition between RNAs for a limiting factor may be a general condition important for function of a variety of post-transcriptional control mechanisms. Splicing and gene expression profiles of 1) wild type yeast cells treated with rapamycin (2 biological replicates) relative to untreated cells and 2) prp4-1 pGAL-IFH1 (down-regulated expression of IFH1 transcription factor(specific for ribosomal protein genes)) relative to prp4-1 yeast.