Transcriptome changes in spliceostatin A treated cells
ABSTRACT: Pre-mRNA in eukaryotes is subjected to post-transcriptional modifications, such as capping, polyadenylation and splicing. It is well known that transcription and post-transcriptional modifications are coupled and that this coupling stimulates post-transcriptional modifications, however, the effects of post-transcriptional modifications on transcription are not fully understood. Here, we report that inhibition of U2 snRNP by a splicing inhibitor, spliceostatin A (SSA), and antisense morpholino oligonucleotide to U2 snRNA caused 3’ end down regulation in a gene-specific manner. We also show that U2 snRNP inhibition resulted in the dephosphorylation of second serine residues (Ser2) within heptad repeats of the C-terminal domain (CTD) of Pol II, which is important for transcription elongation, and this dephosphorylation was correlated with splicing inactivation. Interestingly, removal of SSA from the culture media caused restoration of the Ser2 phosphorylation and expression of the 3’ end, suggesting that transcription elongation resumed. These findings suggest that a novel checkpoint mechanism prevents pre-mRNA accumulation and the production of aberrant proteins translated from pre-mRNA upon splicing deficiencies through the dephosphorylation of CTD Ser2. Treated HeLa cells with methanol or spliceosotain A for 3 hours followed by labelling of nascent transcripts with EU for 1 hour. The EU labelled nascent RNA was purified and analyzed on human exon 1.0ST array. Three biological replicates were used for each treatment.
Project description:In eukaryotes, U1 small nuclear ribonucleoprotein (snRNP) forms spliceosomes in equal stoichiometry with U2, U4, U5 and U6 snRNPs; however, its abundance in human far exceeds that of the other snRNPs. Here we used antisense morpholino oligonucleotide to U1 snRNA to achieve functional U1 snRNP knockdown in HeLa cells, and identified accumulated unspliced pre-mRNAs by genomic tiling microarrays. In addition to inhibiting splicing, U1 snRNP knockdown caused premature cleavage and polyadenylation in numerous pre-mRNAs at cryptic polyadenylation signals, frequently in introns near (<5 kilobases) the start of the transcript. This did not occur when splicing was inhibited with U2 snRNA antisense morpholino oligonucleotide or the U2-snRNP-inactivating drug spliceostatin A unless U1 antisense morpholino oligonucleotide was also included. We further show that U1 snRNA–pre-mRNA base pairing was required to suppress premature cleavage and polyadenylation from nearby cryptic polyadenylation signals located in introns. These findings reveal a critical splicing-independent function for U1 snRNP in protecting the transcriptome, which we propose explains its overabundance. Overall design: Treated HeLa cells with antisense oligos for U1 snRNP or U2 snRNP or control oligo, or methanol or spliceosotain A for 8 hours followed by analysis of total RNA on human tiling 2.0R E array. Three biological replicates were used for each treatment.
Project description:Recent ChIP experiments indicate that spliceosome assembly and splicing can occur cotranscriptionally in S. cerevisiae. However, only a few genes have been examined, and all have long second exons. To extend these studies, we analyzed intron-containing genes with different second exon lengths, by ChIP as well as by whole-genome tiling arrays (ChIP-CHIP). The data indicate that U1 snRNP recruitment is independent of exon length. Recursive splicing constructs, which uncouple U1 recruitment from transcription, suggest that cotranscriptional U1 recruitment contributes to optimal splicing efficiency. In contrast, U2 snRNP recruitment as well as cotranscriptional splicing is deficient on short second exon-genes. We estimate that approximately 90% of endogenous yeast splicing is post-transcriptional, consistent with an analysis of post-transcriptional snRNP-associated pre-mRNA. Keywords: ChIP-CHIP Overall design: ChIP-CHIP was performed on tagged U1, U2, and U5 snRNPs to address spliceosome assembly on intron-containing genes in S. cerevisiae. Data expressed as log2 (immunoprecipitation/input) ratios.
Project description:In eukaryotes, a dynamic ribonucleic protein machine known as the spliceosome catalyzes the removal of introns from pre-messenger RNA (pre-mRNA). Recent studies show the process of RNA-synthesis and RNA-processing to be spatio-temporally coordinated, indicating that RNA splicing takes place in the context of chromatin. H2A.Z is a highly conserved histone variant of the canonical histone H2A. In S. cerevisiae, H2A.Z is deposited into chromatin by the SWR1-complex, is found near the 5’ ends of protein-coding genes, and has been implicated in transcription regulation. Here we show that splicing of intron-containing genes in cells lacking H2A.Z is impaired, particularly under suboptimal splicing conditions. Cells lacking H2A.Z are especially dependent on a functional U2 snRNP, as H2A.Z shows extensive genetic interactions with U2 snRNP associated proteins, and RNA-seq reveals introns with non-consensus branch points are particularly sensitive to H2A.Z loss. Consistently, H2A.Z promotes efficient spliceosomal rearrangements involving the U2 snRNP, as H2A.Z loss results in persistent U2 snRNP association and decreased recruitment of downstream snRNPs to nascent RNA. H2A.Z impairs transcription elongation, suggesting that spliceosome rearrangements are tied to H2A.Z’s role in elongation. Depletion of disassembly factor Prp43 suppresses H2A.Z-mediated splice defects, indicating that, in the absence of H2A.Z, stalled spliceosomes are disassembled and unspliced RNAs are released. Together these data demonstrate that H2A.Z is required for efficient pre-mRNA splicing and indicate a role for H2A.Z in coordinating the kinetics of transcription elongation and splicing. Overall design: Transcriptomes of 11 different cell types in S. cerevisiae generated by sequencing of one to two independent preparations of rRNA-depleteted RNA libraries
Project description:Eukaryotic gene expression requires that RNA Polymerase II (RNAP II) gain access to DNA in the context of chromatin. The C-terminal domain (CTD) of RNAP II recruits chromatin modifying enzymes to promoters, allowing for transcription initiation or repression. Specific CTD phosphorylation marks facilitate recruitment of chromatin modifiers, transcriptional regulators, and RNA processing factors during the transcription cycle. However, the readable code for recruiting such factors is still not fully defined and how CTD modifications affect related families of genes or regional gene expression is not well understood. Here we examine the effects of manipulating the Y1S2P3T4S5P6S7 heptapeptide repeat of the CTD of RNAP II in Schizosaccharomyces pombe by substituting non-phosphorylatable alanines for Ser2 and/or Ser7 and the phosphomimetic glutamic acid for Ser7. Global gene expression analyses were conducted using splicing-sensitive microarrays and validated via RT-qPCR. The CTD mutations did not affect pre-mRNA splicing or snRNA levels. Rather, the data revealed upregulation of subtelomeric genes and alteration of the repressive histone H3 lysine 9 methylation (HeK9me) landscape. The data further indicate that H3K9me and expression status are not fully correlated, suggestive of CTD-dependent subtelomeric repression mechansims that act independently of H3K9me levels. Splicing sensitive S. pombe microarrays (Agilent-027365) were used to compare the splicing and expression profile of four mutant strains relative to WT control with 3-5 biological replicates and dye flipped samples
Project description:Using pol II mutants in human cells we found that slow transcription repositioned specific co-transcriptionally deposited chromatin modifications; H3K36me3 shifted within genes toward 5’ ends and H3K4me2 extended further upstream of start sites. Slow transcription also evoked a hyperphosphorylation of CTD Ser2 residues at 5’ ends of genes that is conserved in yeast. We propose a “dwell-time in the target zone” model to explain the effects of transcriptional dynamics on establishment of co-transcriptionally deposited protein modifications. Promoter-proximal Ser2 phosphorylation is associated with longer pol II dwell time at start sites and reduced transcriptional polarity due to strongly enhanced divergent antisense transcription at promoters. Overall design: The effect of transcription elongation rate on histone H3K36me3, H3K4me2 and pol II CTD phosphorylation was analyzed by ChIP-seq in isogenic human HEK293 cell lines that inducibly express a-amanitin resistant mutants of the RNA polymerase II large subunit with slow elongation rates. Anti-pol II total nascent RNA sequencing (tNET-seq) was developed to assay transcription by WT and slow pol II. Slow pol II mutants in S. cerevisiae were also assayed for pol II CTD Ser2 phosphorylation.
Project description:Transcription by RNA polymerase II (RNAPII) is coupled to mRNA processing and chromatin modifications via the C-terminal domain (CTD) of its largest subunit, consisting of multiple repeats of the heptapeptide YSPTSPS. Pioneering studies showed that CTD serines are differentially phosphorylated along genes in a prescribed pattern during the transcription cycle. Genome-wide analyses challenged this idea, suggesting that this cycle is non-uniform among different genes. Moreover, the respective role of enzymes responsible for CTD modifications remains controversial. Here, we systematically profiled the location of the RNAPII phospho-isoforms in wild type cells and mutants for most CTD modifying enzymes. Together with results of in vitro assays, these data reveal a complex interplay between the modifying enzymes, and provide evidence that the CTD cycle is uniform across genes. We also identify Ssu72 as the Ser7 phosphatase and show that proline isomerization is a key regulator of CTD dephosphorylation at the end of genes. We took a systematic approach to examine the genome-wide distribution of the various CTD modifications using a panel of RNAPII CTD phospho-specific antibodies; both in wild type cells and in mutants for most of the CTD kinases, phosphatases and the isomerase. Immunoprecipitation of CTD phospho-isoforms were done using the following antibodies: H14 and 3E8 for Ser5, H5 and 3E10 for Ser2, 4E12 for Ser7, 8WG16 (anti-Rpb1-CTD) and W0012 (anti-Rpb3) for RNAPII (global localization). A list of the mutant strains and their genotypes can be found in the supplemental files of the related publication. Most ChIPs (in Cy5) were hybridyzed against a non-immunoprecipitated (whole cell extract, WCE) in Cy3. Ssu72, Pti1 and Rpb1 were immunoprecipitated using tagged proteins (3myc-Ssu72, Pti1-3myc, Rpb1-9myc) and the ChIP DNA hybridized in competition with a control ChIP DNA prepared from an isogenic untagged strain (NoTag). ChIP from wild type strains yFR116 (W303) and yFR117 (S288C) were used to obtains wild type profiles that can be compared to mutants strains of the same background. All ChIP-chip experiments were done at least in duplicates. Each microarray was normalized using the Lima Loess and replicates were combined using a weighted average method as previously described (Pokholok et al., 2005).
Project description:This project looks into experimentally identifying all minor introns by knocking down the minor spliceosome's catalytic snRNP, U6atac. Knockdown of U6atac by antisense morpholino followed by examining mRNA splicing by RNA-seq
Project description:Here we examine the role of mRNA splicing in Caenorhabditis elegans RNAi. We find that viable null mutations in U1 and U2-snRNP-specific splicing factor genes cause defects in RNAi. The U1A orthologue rnp-2 is required for normal ERGO-1 Argonaute-class 26G siRNA biogenesis, trans-splicing of the eri-6/7 transcript and targeting of poorly conserved gene transcripts by WAGO Argonaute-class 22G siRNAs. We find that poorly spliced gene transcripts engaged by the siRNA generating machinery are poorly conserved, possess few introns, and often have introns that are divergent from introns found in highly conserved genes. Overall design: Analysis of small RNA populations in wildtype and splicing mutant embryos using next-generation sequencing
Project description:Over-expressed MYC binds to virtually all active promoters within a cell, although with different binding affinities, and modulates gene expression, both positively and negatively. Here, we show that during lymphomagenesis in Eµ-myc transgenic mice, MYC directly up-regulates the transcription of the core snRNP assembly genes, including PRMT5, an arginine methyltransferase, that methylates Sm proteins as an early step in lymphomagenesis. This coordinated regulatory effect is direct and is critical for snRNP biogenesis, the maintenance of effective mRNA splicing and cellular viability in cycling cells, in either fibroblasts or B-cells. mRNA profiles of wild type and pre-tumoral eu-myc mice by deep sequencing, in triplicate, using Illumina NextSeq 500
Project description:There is good evidence for functional interactions between splicing and transcription in eukaryotes, but how and why these processes are coupled remain unknown. Prp5 is an RNA-stimulated ATPase required for pre-spliceosome formation in yeast. We demonstrate through in vivo RNA labelling that, in addition to a splicing defect, the prp5-1 mutation causes a defect in the transcription of intron-containing genes. We present chromatin immunoprecipitation evidence for a transcriptional elongation defect in which RNA polymerase that is phosphorylated at serine 5 of the largest subunit’s heptad repeat accumulates over introns, and that this defect requires the U2 snRNP-associated Cus2p. A similar accumulation of polymerase was observed when pre-spliceosome formation was blocked by a mutation in U2 snRNA. These results indicate the existence of a transcriptional elongation checkpoint that is associated with pre-spliceosome formation during co-transcriptional spliceosome assembly. We propose a role for Cus2p as a potential checkpoint factor in transcription. Examining the Pol II profile in MT strain and WT strain