Project description:Synaptic activity induces well-known changes in enhancer-promoter driven gene expression but also induces changes in splicing and polyadenylation that are understudied. Here, we investigate the mechanism of expression for alternative polyadenylation isoform Homer1a, an immediate early gene essential to synaptic plasticity. We report that neuronal activation, in neuronal cultures and in adult mouse brain, depletes the splice factor U1 snRNP from Homer1 pre-mRNA and that this causes shifted utilization of a cryptic polyadenylation signal within intron 5 resulting in Homer1a expression. Because U1 snRNP is a ubiquitous splice factor, we tested the generality of activity-driven U1 snRNP depletion as a mechanism for gene expression using RNA immunoprecipitation sequencing. Analysis reveals that neuronal activity changes U1 snRNP binding to ~2000 transcripts and for a subset of transcripts, a reduction in U1 snRNP binding was accompanied by utilization of a cryptic intronic polyadenylation site. This subset is enriched for transcripts encoding synaptic proteins involved in excitability control. Genes demonstrating activity-dependent reduced U1 snRNP binding often encode a binding motif for Sam68, a neuronal alternative polyadenylation factor. Findings reveal that activity-driven changes in intron utilization for transcript termination serves an important role in synaptic plasticity.
Project description:The DNA damage response (DDR) involves coordinated control of gene expression and DNA repair. Using deep sequencing we found widespread changes of alternative cleavage and polyadenylation (APA) site usage upon UV-treatment in mammalian cells. APA regulation in the 3’ untranslated region (3’UTR) is substantial, leading to both shortening and lengthening of 3’UTRs. Interestingly, a strong activation of intronic APA sites is detected, resulting in widespread expression of truncated transcripts. Intronic APA events are biased to the 5’ end of genes and affect gene groups with important functions in DDR. Moreover, intronic APA site activation during DDR correlates with a decrease in U1 snRNA levels, and this is reversed by U1 snRNA overexpression. Importantly, U1 snRNA overexpression decreases UV-induced apoptosis. Together, these studies describe a significant gene regulatory scheme in DDR where U1 snRNP impacts gene expression via APA.
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.
Project description:To understand how U4 snRNP regulates premature cleavage and polyadenylation of pre-mRNAs at the transcriptome wide, we conducted mRNA-seq analysis on control, U1 and U4-AMO treated HeLa cells
Project description:To understand how U4 snRNP regulates premature cleavage and polyadenylation of pre-mRNAs at the transcriptome wide, we conducted RNAPII ChIP-seq analysis on control, U1 and U4-AMO treated samples.
Project description:Transcription of the mammalian genome is pervasive, but productive transcription outside of protein-coding genes is limited by unknown mechanisms. In particular, although RNA polymerase II (RNAPII) initiates divergently from most active gene promoters, productive elongation occurs primarily in the sense-coding direction. Here we show in mouse embryonic stem cells that asymmetric sequence determinants flanking gene transcription start sites control promoter directionality by regulating promoter-proximal cleavage and polyadenylation. We find that upstream antisense RNAs are cleaved and polyadenylated at poly(A) sites (PASs) shortly after initiation. De novo motif analysis shows PAS signals and U1 small nuclear ribonucleoprotein (snRNP) recognition sites to be the most depleted and enriched sequences, respectively, in the sense direction relative to the upstream antisense direction. These U1 snRNP sites and PAS sites are progressively gained and lost, respectively, at the 5' end of coding genes during vertebrate evolution. Functional disruption of U1 snRNP activity results in a dramatic increase in promoter-proximal cleavage events in the sense direction with slight increases in the antisense direction. These data suggest that a U1-PAS axis characterized by low U1 snRNP recognition and a high density of PASs in the upstream antisense region reinforces promoter directionality by promoting early termination in upstream antisense regions, whereas proximal sense PAS signals are suppressed by U1 snRNP. We propose that the U1-PAS axis limits pervasive transcription throughout the genome. 3' end sequencing of poly (A) + RNAs in mouse ES cells with and without U1 snRNP inhibition using antisense morpholino oligonucleotides (AMO). Each with two biological replicates.
Project description:To understand how U4 snRNP regulates premature cleavage and polyadenylation of pre-mRNAs at the transcriptome wide, we conducted 3'-seq analysis on control, U1 and U4-AMO treated samples using the Lexogen mRNA 3'-seq kit (Cat. 016.24), which enables accurate quantification of global PAS usage.
Project description:To globally assess the effect of polyadenylation site (PAS) usage upon functional knockdown of U1 snRNP, we carried out PAS-seq analysis with control and U1 AMO-treated HeLa cells using the QuantSeq Rev 3' mRNA sequencing library prep kit (Cat. 016-24).
Project description:This project looks into how U1 snRNP inhibition causes a loss of telescripting through premature cleavage and polyadenylation based on the size and function of human genes.