Dynamic imaging of nascent RNA reveals general principles of transcription dynamics and pervasive recursive splicing [Lariat seq]
Ontology highlight
ABSTRACT: The coupled activities of RNA polymerase and the spliceosome are responsible for the abundance and isoform composition of mRNA in human cells. However, the dynamics of these megadalton enzymatic complexes working in concert on endogenous genes have not been described. Here, we establish a quasi-genome-scale platform for observing synthesis and processing kinetics of single nascent RNA molecules in real time. We find that all observed genes show transcriptional bursting. We also observe large kinetic variation in intron removal for single introns in single cells which is inconsistent with deterministic splice site selection. Transcriptome-wide footprinting of the U2AF complex further reveals widespread splice site selection within introns. We propose and validate a unified theoretical model for transcription and splicing based on pervasive stochastic recursive splicing.
Project description:The coupled activities of RNA polymerase and the spliceosome are responsible for the abundance and isoform composition of mRNA in human cells. However, the dynamics of these megadalton enzymatic complexes working in concert on endogenous genes have not been described. Here, we establish a quasi-genome-scale platform for observing synthesis and processing kinetics of single nascent RNA molecules in real time. We find that all observed genes show transcriptional bursting. We also observe large kinetic variation in intron removal for single introns in single cells which is inconsistent with deterministic splice site selection. Transcriptome-wide footprinting of the U2AF complex further reveals widespread splice site selection within introns. We propose and validate a unified theoretical model for transcription and splicing based on pervasive stochastic recursive splicing.
Project description:The coupled activities of RNA polymerase and the spliceosome are responsible for the abundance and isoform composition of mRNA in human cells. However, the dynamics of these megadalton enzymatic complexes working in concert on endogenous genes have not been described. Here, we establish a quasi-genome-scale platform for observing synthesis and processing kinetics of single nascent RNA molecules in real time. We find that all observed genes show transcriptional bursting. We also observe large kinetic variation in intron removal for single introns in single cells which is inconsistent with deterministic splice site selection. Transcriptome-wide footprinting of the U2AF complex further reveals widespread splice site selection within introns. We propose and validate a unified theoretical model for transcription and splicing based on pervasive stochastic recursive splicing.
Project description:The coupled activities of RNA polymerase and the spliceosome are responsible for the abundance and isoform composition of mRNA in human cells. However, the dynamics of these megadalton enzymatic complexes working in concert on endogenous genes have not been described. Here, we establish a quasi-genome-scale platform for observing synthesis and processing kinetics of single nascent RNA molecules in real time. We find that all observed genes show transcriptional bursting. We also observe large kinetic variation in intron removal for single introns in single cells which is inconsistent with deterministic splice site selection. Transcriptome-wide footprinting of the U2AF complex further reveals widespread splice site selection within introns. We propose and validate a unified theoretical model for transcription and splicing based on pervasive stochastic recursive splicing.
Project description:The coupled activities of RNA polymerase and the spliceosome are responsible for the abundance and isoform composition of mRNA in human cells. However, the dynamics of these megadalton enzymatic complexes working in concert on endogenous genes have not been described. Here, we establish a quasi-genome-scale platform for observing synthesis and processing kinetics of single nascent RNA molecules in real time. We find that all observed genes show transcriptional bursting. We also observe large kinetic variation in intron removal for single introns in single cells which is inconsistent with deterministic splice site selection. Transcriptome-wide footprinting of the U2AF complex further reveals widespread splice site selection within introns. We propose and validate a unified theoretical model for transcription and splicing based on pervasive stochastic recursive splicing.
Project description:The coupled activities of RNA polymerase and the spliceosome are responsible for the abundance and isoform composition of mRNA in human cells. However, the dynamics of these megadalton enzymatic complexes working in concert on endogenous genes have not been described. Here, we establish a quasi-genome-scale platform for observing synthesis and processing kinetics of single nascent RNA molecules in real time. We find that all observed genes show transcriptional bursting. We also observe large kinetic variation in intron removal for single introns in single cells which is inconsistent with deterministic splice site selection. Transcriptome-wide footprinting of the U2AF complex further reveals widespread splice site selection within introns. We propose and validate a unified theoretical model for transcription and splicing based on pervasive stochastic recursive splicing.
Project description:The coupled activities of RNA polymerase and the spliceosome are responsible for the abundance and isoform composition of mRNA in human cells. However, the dynamics of these megadalton enzymatic complexes working in concert on endogenous genes have not been described. Here, we establish a quasi-genome-scale platform for observing synthesis and processing kinetics of single nascent RNA molecules in real time. We find that all observed genes show transcriptional bursting. We also observe large kinetic variation in intron removal for single introns in single cells which is inconsistent with deterministic splice site selection. Transcriptome-wide footprinting of the U2AF complex further reveals widespread splice site selection within introns. We propose and validate a unified theoretical model for transcription and splicing based on pervasive stochastic recursive splicing.
Project description:Recent studies have shown that expression of many genes with exceptionally long introns in the mammalian brain can be perturbed by regulatory factors linked to neurodevelopmental or neurodegenerative disorders1-3, suggesting unique regulatory mechanisms. Here we identify functional recursive splice sites (RSS) in long introns of genes expressed in the brain. These RSS are highly conserved in genes with extreme length across diverse vertebrate species and permit step-wise removal of long introns via recursive splicing. Recursive splicing requires initial definition of a “recursive exon” that is located downstream of RSS, and most often contains premature stop codons. Moreover, we show that RSS create a splicing switch driven by splice site competition in order to distinguish primary mRNA isoforms from alternative isoforms that are prevalent in long genes. The recursive exon is not detectable in the dominant mRNA isoform due to recursive splicing, but is completely included when cryptic promoters or other cryptic exons are used. Thus, by coupling inclusion of recursive exons with the use of cryptic elements, RSS act to distinguish new mRNA isoforms emerging from long genes.
Project description:Long introns with short exons in vertebrate genes are thought to require spliceosome assembly across exons (exon definition), rather than introns, thereby requiring transcription of an exon to splice an upstream intron. Here, we developed CoLa-seq (co-transcriptional lariat sequencing) to investigate the timing and determinants of co-transcriptional splicing genome wide. Unexpectedly, 90% of all introns, including long introns, can splice before transcription of a downstream exon, indicating that exon definition is not obligatory for most human introns. Still, splicing timing varies dramatically across introns, and various genetic elements determine this variation. Strong U2AF2 binding to the polypyrimidine tract predicts early splicing, explaining exon definition-independent splicing. Together, our findings question the essentiality of exon definition and reveal features beyond intron and exon length that are determinative for splicing timing.
Project description:We report a novel single-cell total RNA-seq method, RamDA-seq, by combining a novel reverse transcription (RT) technology, RT with random displacement amplification (RT-RamDA), and not-so-random (NSR) primers. RT-RamDA provides global cDNA amplification directly from RNA during RT without any universal adopters, which benefits RT efficiency, simplification of the procedure, avoiding the step of PCR amplification, and decontamination of genomic DNA. NSR enables random priming while preventing cDNA synthesis from rRNAs. RamDA-seq showed high sensitivity to non-poly(A) RNAs and full-length coverage even for extremely long transcripts (>10 kb). Moreover, RamDA-seq revealed recursive splicing, a multi-step, splicing, within > 300 kbp-long introns. Finally, RamDA-seq enabled the first genome-wide analysis of enhancer RNAs (eRNAs) in single cells.
Project description:The U2AF heterodimer has been well studied for its role in defining functional 3M-bM-^@M-^Y splice sites in pre-mRNA splicing, but many fundamental questions still remain unaddressed regarding the function of U2AF in mammalian genomes. Through genome-wide analysis of U2AF-RNA interactions, we report that U2AF has the capacity to directly define ~88% of functional 3M-bM-^@M-^Y splice sites in the human genome, but numerous U2AF binding events also occur in intronic locations. Mechanistic dissection reveals that upstream intronic binding events interfere with the immediate downstream 3M-bM-^@M-^Y splice site associated with either the alternative exon to cause exon skipping or with the competing constitutive exon to induce exon inclusion. We further demonstrate partial functional impairment with mutations in U2AF35, but not U2AF65, in regulated splicing. These findings reveal the genomic function and regulatory mechanism of U2AF in both normal and disease states. Examination of U2AF heterodimer regulated splicing in Hela cells with CLIP-seq (U2AF65), paired-end RNA-seq (si-NC and si-U2AF65) and RASL-seq (respective three biological replicates of WT, si-NC, si-U2AF65, si-U2AF35, si-NC + pcDNA3.0, si-U2AF65 + pcDNA3.0, and si-U2AF65 + Flag-U2AF35)