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:U1 snRNP plays an essential role in initiating spliceosome assembly, yet the mechanism underlying its synergy with other splicing regulators for efficient spliceosome assembly remains elusive. Here we identify ZFP207 as a key regulator of U1 snRNP function that substantially promotes spliceosome assembly. Acute depletion of ZFP207 results in a series of molecular phenotypes indicative of U1 snRNP dysregulation. Mechanistically, the N-terminal zinc finger domains of ZFP207 directly bind to the stem-loop 3 (SL3) of U1 snRNA, while its C-terminal intrinsically disordered regions (IDRs) undergo phase separation to form biomolecular condensates with U1 snRNP. These condensates create a crowded molecular environment that increases the local concentration of splicing snRNPs and regulators, thereby accelerating the speed of spliceosome assembly by facilitating interactions between U1 snRNP and other snRNPs. Collectively, our study demonstrates the critical role of phase separation in ensuring effective U1 snRNP function and promoting efficient spliceosome assembly.
Project description:U1 snRNP plays an essential role in initiating spliceosome assembly, yet the mechanism underlying its synergy with other splicing regulators for efficient spliceosome assembly remains elusive. Here we identify ZFP207 as a key regulator of U1 snRNP function that substantially promotes spliceosome assembly. Acute depletion of ZFP207 largely recapitulates the molecular phenotypes observed with the depletion of SNRNP70, a core component of U1 snRNP. Mechanistically, the N-terminal zinc finger domains of ZFP207 directly bind to U1 snRNA, while its C-terminus undergoes phase separation via intrinsically disordered regions (IDRs) to forms biomolecular condensates with U1 snRNP. These condensates create a crowded molecular environment that increases the local concentration of splicing snRNPs and regulators, thereby accelerating the speed of spliceosome assembly by facilitating interactions between U1 snRNP and other snRNPs. Collectively, our study demonstrates the critical role of phase separation in ensuring proper U1 snRNP function and efficient spliceosome assembly.
Project description:U1 snRNP plays an essential role in initiating spliceosome assembly, yet the mechanism underlying its synergy with other splicing regulators for efficient spliceosome assembly remains elusive. Here we identify ZFP207 as a key regulator of U1 snRNP function that substantially promotes spliceosome assembly. Acute depletion of ZFP207 largely recapitulates the molecular phenotypes observed with the depletion of SNRNP70, a core component of U1 snRNP. Mechanistically, the N-terminal zinc finger domains of ZFP207 directly bind to U1 snRNA, while its C-terminus undergoes phase separation via intrinsically disordered regions (IDRs) to forms biomolecular condensates with U1 snRNP. These condensates create a crowded molecular environment that increases the local concentration of splicing snRNPs and regulators, thereby accelerating the speed of spliceosome assembly by facilitating interactions between U1 snRNP and other snRNPs. Collectively, our study demonstrates the critical role of phase separation in ensuring proper U1 snRNP function and efficient spliceosome assembly.
Project description:Individual-nucleotide resolution UV-crosslinking and immunoprecipitation (iCLIP) combined with high-throughput sequencing was performed to generate genome-wide binding maps of two U1-snRNP proteins: U1C and U1-70K in Trypanosoma brucei. 3 (2) biological replicates of U1C (U1-70K) -specific co-immunoprecipitated RNA after UV-crosslinking
Project description:Regulation of RNA polymerase II (Pol II) elongation is a critical step in gene regulation. Here, we report that U1 snRNP recognition and transcription pausing at stable nucleosomes are linked through premature polyadenylation signal (PAS) termination. By generating RNA exosome conditional deletion mouse embryonic stem cells, we identified a large class of polyadenylated short transcripts in the sense direction destabilized by the RNA exosome. These PAS termination events are enriched at the first few stable nucleosomes flanking CpG islands and suppressed by U1 snRNP. Thus, promoter-proximal Pol II pausing consists of two processes: TSS-proximal and +1 stable nucleosome pausing, with PAS termination coinciding with the latter. While pausing factors NELF/DSIF only function in the former step, flavopiridol-sensitive mechanism(s) and Myc modulate both steps. We propose that premature PAS termination near the nucleosome-associated pause site represents a common transcriptional elongation checkpoint regulated by U1 snRNP recognition, nucleosome stability, and Myc activity.
Project description:Regulation of RNA polymerase II (Pol II) elongation is a critical step in gene regulation. Here, we report that U1 snRNP recognition and transcription pausing at stable nucleosomes are linked through premature polyadenylation signal (PAS) termination. By generating RNA exosome conditional deletion mouse embryonic stem cells, we identified a large class of polyadenylated short transcripts in the sense direction destabilized by the RNA exosome. These PAS termination events are enriched at the first few stable nucleosomes flanking CpG islands and suppressed by U1 snRNP. Thus, promoter-proximal Pol II pausing consists of two processes: TSS-proximal and +1 stable nucleosome pausing, with PAS termination coinciding with the latter. While pausing factors NELF/DSIF only function in the former step, flavopiridol-sensitive mechanism(s) and Myc modulate both steps. We propose that premature PAS termination near the nucleosome-associated pause site represents a common transcriptional elongation checkpoint regulated by U1 snRNP recognition, nucleosome stability, and Myc activity.
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:U1 snRNP plays an essential role in initiating spliceosome assembly, yet the mechanism underlying its synergy with other splicing regulators for efficient spliceosome assembly remains elusive. Here we identify ZFP207 as a key regulator of U1 snRNP function that substantially promotes spliceosome assembly. Acute depletion of ZFP207 recapitulates the molecular phenotypes observed with the depletion of SNRNP70, a core component of U1 snRNP. Mechanistically, the N-terminal zinc finger domains of ZFP207 directly bind to U1 snRNA, while its C-terminus undergoes phase separation via intrinsically disordered regions (IDRs). The coordination between the N-terminus and C-terminus of ZFP207 drives the formation of biomolecular condensate with U1 snRNP, which creates a molecular environment to promote spliceosome assembly by facilitating the interactions between U1 snRNP and other splicing regulators. Collectively, our study demonstrates the critical role of ZFP207-mediated phase separation in ensuring proper U1 snRNP function and spliceosome assembly.