Project description:In the earliest step of spliceosome assembly, the two splice sites flanking an intron are brought into proximity by U1 snRNP and U2AF. The mechanism that facilitates this intron looping is poorly understood. Using a CRISPR interference-based approach to halt RNA polymerase II transcription in the middle of introns, we discovered that the 5 splice site base pairs with a U1 snRNA that is tethered to RNA polymerase II during intron synthesis. Correlation with splicing outcomes demonstrate that these associations are functional. The interactions between 5 splice sites, U1 snRNP, and elongating RNA polymerase II occurs genome-wide. Our findings reveal that during intron synthesis the upstream 5 splice site remains attached to the transcriptional machinery and is thus brought into proximity of the 3 splice site to enable rapid splicing.
Project description:Alternative pre-mRNA splicing increases proteomic diversity and provides a potential mechanism underlying both phenotypic diversity and susceptibility to genetic disorders in human populations. To investigate the variation in splicing among humans on a genomewide scale, we use a comprehensive exon-targeted microarray to examine alternative splicing in lymphoblasts derived from the CEPH HapMap population. We show the identification of transcripts containing annotated and novel sequence verified exon skipping, intron retention, and cryptic splice site usage that are specific between individuals. Using family-based linkage analysis, we demonstrate Mendelian inheritance and segregation of specific splice isoforms with regulatory haplotypes for three genes. Allelic association was further used to identify individual SNPs or regulatory haplotype blocks linked to the alternative splicing event, taking advantage of the high-resolution genotype information from the CEPH HapMap population. Keywords: Comparative genomic hybridiation within a 3 generation pedigree
Project description:Alternative splicing (AS) plays key roles in plant development and responses to environmental changes. However, the mechanisms underlying AS divergence (differential expression of transcript isoforms resulting from alternative splicing) in plant accessions and its contributions to responses to environmental stimuli remain unclear. In this study, we investigated genome-wide variation of AS in Arabidopsis thaliana accessions Col-0, Bur-0, C24, Kro-0, and Ler-1, as well as their F1 hybrids, and characterized the regulatory mechanisms for AS divergence by RNA sequencing (RNA-seq). We found that most of the divergent AS events in Arabidopsis accessions were cis-regulated by sequence variation, including those in core splice site and splicing motifs. Many genes that differed in AS between Col-0 and Bur-0 were involved in stimulus responses. Further genome-wide association analyses of 22 environmental variables showed that SNPs influencing known splice site strength were also associated with environmental stress responses. These results demonstrate that cis-variation in genomic sequences among Arabidopsis accessions was the dominant contributor to AS divergence, and it may contribute to differences in environmental responses among Arabidopsis accessions.
Project description:Spliced messages constitute one-fourth of expressed mRNAs in the yeast Saccharomyces cerevisiae, and most mRNAs in metazoans. Splicing requires 5' splice site (5'SS), branch point (BP), and 3' splice site (3'SS) elements, but the role of the BP in splicing control is poorly understood because BP identification remains difficult. We developed a high-throughput method, Branch-seq, to map BP and 5'SS of isolated RNA lariats. Applied to S. cerevisiae, Branch-seq detected 76% of expressed, annotated BPs and identified a comparable number of novel BPs. We used RNA-seq to confirm associated 3'SS locations, identifying some 200 novel splice junctions, including an AT-AC intron. We show that several yeast introns use two or even three different BPs, with effects on 3'SS choice, protein coding potential, or RNA stability and identify novel introns whose splicing changes during meiosis or in response to stress. Together, these findings reveal BP-based regulation and demonstrate unanticipated complexity of splicing in yeast. 1 Lariat-seq experiment library. 3 barcoded Branch-seq libraries that make up one experiment. 26 RNA-seq samples, 2 biological replicates of each.
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.