Project description:There has been a surge of interest towards targeting protein synthesis to treat diseases and extend lifespan. Despite the progress, few options are available to assess translation in live animals, as their complexity limits the repertoire of experimental tools to monitor and manipulate processes within organs and individual cells. It this study, we developed a labeling-free method for measuring organ- and cell-type-specific translation elongation rates in vivo. It is based on time-resolved delivery of translation initiation and elongation inhibitors in live animals followed by ribosome profiling. It also reports translation initiation sites in an organ-specific manner. Using this method, we found that the elongation rates differ more than 50% among mouse organs and determined them to be 6.8, 5.0, and 4.3 amino acids per second for liver, kidney, and skeletal muscle, respectively. We further found that the elongation rate is reduced by 20% between young adulthood and mid-life. Thus, translation, a major metabolic process in cells, is tightly regulated at the level of elongation of nascent polypeptide chains.
Project description:There has been a surge of interest towards targeting protein synthesis to treat diseases and extend lifespan. Despite the progress, few options are available to assess translation in live animals, as their complexity limits the repertoire of experimental tools to monitor and manipulate processes within organs and individual cells. It this study, we developed a labeling-free method for measuring organ- and cell-type-specific translation elongation rates in vivo. It is based on time-resolved delivery of translation initiation and elongation inhibitors in live animals followed by ribosome profiling. It also reports translation initiation sites in an organ-specific manner. Using this method, we found that the elongation rates differ more than 50% among mouse organs and determined them to be 6.8, 5.0 and 4.3 amino acids per second for liver, kidney, and skeletal muscle, respectively. We further found that the elongation rate is reduced by 20% between young adulthood and mid-life. Thus, translation, a major metabolic process in cells, is tightly regulated at the level of elongation of nascent polypeptide chains.
Project description:The rate of transcription elongation plays important roles in the timing of expression of full-length transcripts as well as for the regulation of alternative splicing. In this study we coupled Bru-Seq technology with 5,6-dichlorobenzimidazole 1-M-NM-2-D-ribofuranoside (DRB) to estimate the elongation rates of over 2,000 individual genes in human cells. This technique, BruDRB-Seq, revealed gene-specific differences in elongation rates with a median rate of around 1.5 kb/min. We found that genes with fast elongation rates showed higher densities of H3K79m2 and H4K20me1 marks compared to slower elongating genes. Furthermore, fast elongation rates had a positive correlation with gene length, low complexity DNA sequence and distance from nearest active transcription unit. Features that negatively correlated with elongation rate included exon density and the number of LINE sequences in the gene. The BruDRB-Seq technique offers new opportunities to interrogate mechanisms of regulation of transcription elongation. Measurement of RNA Pol II elogation rate. Normal fibroblasts (HF1 and TM), Cockayne syndrome group B fibroblasts, K562 and MCF-7 cells were exposed to DRB for 60 minutes, after which a washout was performed. Nascent RNA was labeled using bromouridine for 10 minutes immediately after the washout. The genomic region extending from actice Trancription Start Sites was used to determine the gene's elongation rate. Please note that the nf_0h_3* samples are duplicated sample records of GSM1062445 and GSM1062446, for the convenient retrieval of the complete raw data from SRA.
Project description:Recent studies reveal a striking phenomenon that RNA Polymerase II (Pol II) appears to travel on gene body in an accelerated fashion, but the mechanism has remained unknown. We performed synchronized transcription coupled with deep sequencing, observing an inverse relationship between initial rate and acceleration in different cell types. We directly tested several correlative events and detected a positive contribution of the splicing commitment factor SRSF2 to Pol II acceleration, suggesting a functional benefit of co-transcriptional pre-mRNA splicing in transcription elongation. Unexpectedly, we found that perturbation of Pol II Ser2 phosphorylation had little impact on Pol II elongation or acceleration. While H3K79me2 has been positively correlated with Pol II elongation, we showed that reduction of this histone modification event actually accelerated Pol II elongation. Together, these data suggest a combined effect of gradual gain-of-competence and gradual lost-of-epigenetic barriers as the mechanism for accelerated Pol II elongation. DRB time-course releasing assay under functional perturbation
Project description:To study the impact of the RNA polymerase II (Pol II) elongation rate on gene expression, we used CRISPR-Cas9 genome editing in S. pombe to generate a "slow" Pol II mutant with decreased elongation rate. Although the mutation is well tolerated as far as cell growth is concerned, transcriptomic analyses revealed that the slow mutant tends to terminate transcription prematurely. We distinguished two mechanisms by which premature termination affects gene expression in the slow mutant: It either (1) shortens 3'UTR, or (2) derepresses protein coding genes by prematurely terminating upstream interfering RNAs. Strikingly, the genes affected by these mechanisms are enriched for genes involved in phosphate uptake and purine synthesis, two processes essential for the maintenance of the nucleotide pool of the cell. Together with evidences that nucleotides are conditional for Pol II processive elongation, our results suggest that Pol II elongation rate acts as both sensor and effector in response to nucleotide depletion.
Project description:The Pol II elongation rate influences poly(A) site selection, with slow and fast Pol II derivatives causing upstream and downstream shifts, respectively, in poly(A) site utilization. In yeast, depletion of either of the histone chaperones FACT or Spt6 causes an upstream shift of poly(A) site use that strongly resembles the poly(A) profiles of slow Pol II mutant strains. Like slow Pol II mutant strains, Spt6- and FACT-depleted cells exhibit processivity defects, indicating that both Spt6 and FACT stimulate the Pol II elongation rate. Poly(A) profiles of some genes show atypical downstream shifts; this subset of genes overlaps well for FACT- or Spt6- depleted strains, but it is different from the atypical genes in Pol II speed mutant strains. In contrast, depletion of histone H3 or H4 causes a downstream shift of poly(A) sites for most genes, indicating that nucleosomes inhibit the Pol II elongation rate in vivo. Thus, chromatin-based control of the Pol II elongation rate is a potential mechanism, distinct from direct effects on the cleavage/polyadenylation machinery, to regulate alternative polyadenylation in response to genetic or environmental changes.
Project description:The rate of transcription elongation plays important roles in the timing of expression of full-length transcripts as well as for the regulation of alternative splicing. In this study we coupled Bru-Seq technology with 5,6-dichlorobenzimidazole 1-β-D-ribofuranoside (DRB) to estimate the elongation rates of over 2,000 individual genes in human cells. This technique, BruDRB-Seq, revealed gene-specific differences in elongation rates with a median rate of around 1.5 kb/min. We found that genes with fast elongation rates showed higher densities of H3K79m2 and H4K20me1 marks compared to slower elongating genes. Furthermore, fast elongation rates had a positive correlation with gene length, low complexity DNA sequence and distance from nearest active transcription unit. Features that negatively correlated with elongation rate included exon density and the number of LINE sequences in the gene. The BruDRB-Seq technique offers new opportunities to interrogate mechanisms of regulation of transcription elongation.
Project description:Elongation factor Paf1C regulates several stages of the RNA polymerase II (Pol II) transcription cycle, although it is unclear how it modulates Pol II distribution and progression in mammalian cells. We found that conditional ablation of Paf1 resulted in the accumulation of unphosphorylated and Ser5 phosphorylated Pol II around promoter proximal regions and within the first 20-30 kb of gene bodies, respectively. Paf1 ablation did not impact the recruitment of other key elongation factors, namely, Spt5, Spt6, and the FACT complex, suggesting that Paf1 function may be mechanistically distinguishable from each of these factors. Moreover, loss of Paf1 triggered an increase in TSS-proximal nucleosome occupancy, which could impose a considerable barrier to Pol II elongation past TSS-proximal regions. Remarkably, accumulation of Ser5P in the first 20-30 kb coincided with reductions in histone H2B ubiquitylation within this region. Furthermore, we show that nascent RNA species accumulate within this window, suggesting a mechanism whereby Paf1 loss leads to aberrant, prematurely terminated transcripts and diminution of full-length transcripts. Importantly, we found that loss of Paf1 results in Pol II elongation rate defects with significant rate compression. Our findings suggest that Paf1C is critical for modulating Pol II elongation rates by functioning beyond the pause-release step as an "accelerator" over specific early gene body regions.