RNA polymerase II dynamics and mRNA stability feedback scale mRNA amounts with cell size
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ABSTRACT: A fundamental feature of cellular growth is that total protein and RNA amounts increase with cell size to keep concentrations approximately constant. A key component to this is that global transcription rates increase in larger cells. Here, we identify RNAPII as the limiting factor scaling mRNA transcription with cell size in budding yeast, as transcription is highly sensitive to the dosage of RNAPII but not to other components of the transcriptional machinery. Our experiments support a dynamic equilibrium model where global RNAPII transcription at a given size is set by the mass-action recruitment kinetics of unengaged nucleoplasmic RNAPII to the genome. However, this only drives a sub-linear increase in transcription with size, which is then partially compensated for by a decrease in mRNA decay rates as cells enlarge. Thus, limiting RNAPII and feedback on mRNA stability work in concert to scale mRNA amounts with cell size.
Project description:Over-expression of the Myc transcription factor causes its widespread interaction with regulatory domains in the genome, but leads to the up- and down-regulation of discrete sets of genes. The molecular determinants of these selective transcriptional responses remain elusive. Here, we present an integrated time-course analysis of transcription and mRNA dynamics following Myc activation in proliferating mouse fibroblasts, based on chromatin immunoprecipitation, metabolic labeling of newly synthesized RNA, extensive sequencing and mathematical modeling. Transcriptional activation correlated with the highest increases in Myc binding at promoters. Repression followed a reciprocal scenario, with the lowest gains in Myc binding. Altogether, the relative abundance (henceforth, “share”) of Myc at promoters was the strongest predictor of transcriptional responses in diverse cell types, predominating over Myc’s association with the co-repressor Miz1. Myc activation elicited immediate loading of RNAPII at activated promoters, followed by increases in pause-release5, while repressed promoters showed opposite effects. Gains and losses in RNAPII loading were proportional to the changes in the Myc share, suggesting that repression by Myc may be largely indirect, owing - at least in part - to competition for limiting amounts of RNAPII. Secondary to the changes in RNAPII loading, the dynamics of elongation and pre-mRNA processing were also rapidly altered at Myc regulated genes, leading to the transient accumulation of partially or aberrantly processed mRNAs. Altogether, our results shed light on how over-expressed Myc alters the various phases of the RNAPII cycle and the resulting transcriptional response.
Project description:Over-expression of the Myc transcription factor causes its widespread interaction with regulatory domains in the genome, but leads to the up- and down-regulation of discrete sets of genes. The molecular determinants of these selective transcriptional responses remain elusive. Here, we present an integrated time-course analysis of transcription and mRNA dynamics following Myc activation in proliferating mouse fibroblasts, based on chromatin immunoprecipitation, metabolic labeling of newly synthesized RNA, extensive sequencing and mathematical modeling. Transcriptional activation correlated with the highest increases in Myc binding at promoters. Repression followed a reciprocal scenario, with the lowest gains in Myc binding. Altogether, the relative abundance (henceforth, “share”) of Myc at promoters was the strongest predictor of transcriptional responses in diverse cell types, predominating over Myc’s association with the co-repressor Miz1. Myc activation elicited immediate loading of RNAPII at activated promoters, followed by increases in pause-release5, while repressed promoters showed opposite effects. Gains and losses in RNAPII loading were proportional to the changes in the Myc share, suggesting that repression by Myc may be largely indirect, owing - at least in part - to competition for limiting amounts of RNAPII. Secondary to the changes in RNAPII loading, the dynamics of elongation and pre-mRNA processing were also rapidly altered at Myc regulated genes, leading to the transient accumulation of partially or aberrantly processed mRNAs. Altogether, our results shed light on how over-expressed Myc alters the various phases of the RNAPII cycle and the resulting transcriptional response.
Project description:Over-expression of the Myc transcription factor causes its widespread interaction with regulatory domains in the genome, but leads to the up- and down-regulation of discrete sets of genes. The molecular determinants of these selective transcriptional responses remain elusive. Here, we present an integrated time-course analysis of transcription and mRNA dynamics following Myc activation in proliferating mouse fibroblasts, based on chromatin immunoprecipitation, metabolic labeling of newly synthesized RNA, extensive sequencing and mathematical modeling. Transcriptional activation correlated with the highest increases in Myc binding at promoters. Repression followed a reciprocal scenario, with the lowest gains in Myc binding. Altogether, the relative abundance (henceforth, “share”) of Myc at promoters was the strongest predictor of transcriptional responses in diverse cell types, predominating over Myc’s association with the co-repressor Miz1. Myc activation elicited immediate loading of RNAPII at activated promoters, followed by increases in pause-release5, while repressed promoters showed opposite effects. Gains and losses in RNAPII loading were proportional to the changes in the Myc share, suggesting that repression by Myc may be largely indirect, owing - at least in part - to competition for limiting amounts of RNAPII. Secondary to the changes in RNAPII loading, the dynamics of elongation and pre-mRNA processing were also rapidly altered at Myc regulated genes, leading to the transient accumulation of partially or aberrantly processed mRNAs. Altogether, our results shed light on how over-expressed Myc alters the various phases of the RNAPII cycle and the resulting transcriptional response.
Project description:The C-terminal domain (CTD) of RNA polymerase II (RNAPII) is composed of heptapeptide repeats, which play a key regulatory role in gene expression. Using genetic interaction and mRNA expression analysis we found that truncating the CTD resulted in distinct changes to cellular function. Truncating the CTD altered RNAPII occupancy to not only cause decreases, but also increases in mRNA levels. The latter were largely mediated by promoter elements, and in part were linked to the transcription factor Rpn4. The mediator subunit Cdk8 was enriched at promoters of these genes, and its removal not only restored normal mRNA and RNAPII occupancy levels, but also reduced the abnormally high cellular amounts of Rpn4. This suggested a positive role of Cdk8 in relationship to RNAPII, which contrasted with the negative role at the activated INO1 gene. Here, loss of CDK8 suppressed the reduced mRNA expression and RNAPII occupancy levels of CTD truncation mutants.
Project description:We have taken five different time points of a Yeast culture in exponential grow in rich medium, each one elapsed ten minutes from de previous one (from OD600 0.36 to 0.47). Then, for each time point we have measured the transcription rates (TR) and mRNA amounts (RA) for all the genes using the Genomic run-on (GRO) technique . For each time point we have measured the transcription rates (GRO) with 3 replicates (except for the t2 that only has 2 replicates due to technical problems) and mRNA amounts (cDNA RP) with 3 replicates for all the genes. The data were normalized using a gDNA hybridization for each filter.
Project description:Complex molecular responses preserve gene expression accuracy and genome integrity in the face of environmental perturbations. Here we report that, in response to UV-irradiation, RNA Polymerase II (RNAPII) molecules are dynamically and synchronously released from promoter-proximal regions to promote uniform and accelerated scanning of the whole transcribed genome. The maximised influx of de novo released RNAPII correlates with increased sensing of damaged sites, as confirmed by RNAPII accumulation at dipyrimidine sites and by the average slow-down of elongation rates in gene bodies. By triggering this transcription elongation ‘safe’ mode, endangered cells guarantee an efficient DNA repair regardless of damage location, gene size and transcription level. Accordingly, in clinically-relevant samples we detect low and homogenous rates of mutational signatures associated with UV-irradiation or cigarette-smoke across all active genes. Together, our data highlight a novel functional advantage associated with regulation of promoter-proximal pausing and provide unanticipated insights into the mechanism underlying the central role of active transcription in shaping the mutagenic landscape of cancer genomes.
Project description:Plants possess a cold acclimation system to acquire freezing tolerance through pre-exposure to non-freezing low temperatures. The transcriptional cascade of C-repeat binding factors (CBFs)/dehydration response element-binding factors (DREBs) is considered a major transcriptional regulatory pathway during cold acclimation. However, little is known regarding the functional significance of mRNA stability regulation in the response of gene expression to cold stress. The actual level of individual mRNAs is determined by a balance between mRNA synthesis and degradation. Therefore, it is important to assess the regulatory steps to increase our understanding of gene regulation. Here, we analyzed temporal changes in mRNA amounts and half-lives in response to cold stress in Arabidopsis cell cultures based on genome-wide analysis. In this mRNA decay array method, mRNA half-life measurements and microarray analyses were combined. In addition, temporal changes in the integrated value of transcription rates were estimated from the above two parameters using a mathematical approach. Our results showed that several cold-responsive genes, including Cold-regulated 15a, were relatively destabilized, whereas the mRNA amounts were increased during cold treatment by accelerating the transcription rate to overcome the destabilization. Considering the kinetics of mRNA synthesis and degradation, this apparently contradictory result supports that mRNA destabilization is advantageous for the swift increase in CBF-responsive genes in response to cold stress.
Project description:Transcriptomics data obtained from limiting amounts of mRNA is often noisy, providing primarily qualitative changes in transcript expressions. So far, technical variations arising out of the library preparation protocols have not been adequately characterized at reduced levels of mRNA. Here, we generated sequencing libraries from limiting amounts of mRNA using three amplification-based methods, viz. Smart-seq, DP-seq and CEL-seq, and demonstrated significant technical variations in these libraries. Reduction in mRNA levels led to inefficient amplification of the majority of low to moderately expressed transcripts. Furthermore, stochasticity in primer hybridization and/or enzyme incorporation was magnified during the amplification step resulting in significant distortions in fold changes of the transcripts. Consequently, the majority of the differentially expressed transcripts identified were either high-expressed and/or exhibited high fold changes. High technical variations, which were sequencing depth independent, ultimately masked subtle biological differences mandating the development of improved amplification-based strategies for quantitative transcriptomics from limiting amounts of mRNA.
Project description:We analyzed the effect of SAC3, SUS1 and SRC1 on the transcription rates, mRNA stabilities and mRNA levels by doing GRO experiments in a deletion mutants and the partial C-truncated version of Sac3 comparing with a wild type. Some data for mRNA amounts (sus1 ans src1 mutants) are not included because were already in GEO database: GSE920 and GSE6370 accession numbers.