Project description:Alternative polyadenylation generates numerous 3’ mRNA isoforms that can differ in their stability, structure, and function. These isoforms can be used to map mRNA stabilizing and destabilizing elements within 3’ untranslated regions (3’UTRs). Here, we examine how environmental conditions affect 3’ mRNA isoform turnover and structure in yeast cells on a transcriptome scale. Isoform stability broadly increases when cells grow more slowly, with relative half-lives of most isoforms being well correlated across multiple conditions. Surprisingly, dimethyl sulfate probing reveals that individual 3’ isoforms have similar structures across different conditions, in contrast to the extensive structural differences that can exist between closely related isoforms in an individual condition. Unexpectedly, most mRNA stabilizing and destabilizing elements function only in a single growth condition. The genes associated with some classes of condition-specific stability elements are enriched for different functional categories, suggesting that regulated mRNA stability might contribute to adaptation to different growth environments. Condition-specific stability elements do not result in corresponding condition-specific changes in steady-state mRNA isoform levels. This observation is consistent with a compensatory mechanism between polyadenylation and stability, and it suggests that condition-specific mRNA stability elements might largely reflect condition-specific regulation of mRNA 3’ end formation.
Project description:We measured half-lives of 21,248 mRNA 3’ isoforms in yeast by rapidly depleting RNA polymerase II from the nucleus and performing direct RNA sequencing throughout the decay process. Interestingly, the half-lives of mRNA isoforms from the same gene, including nearly identical isoforms, often vary widely. Based on clusters of isoforms with different half-lives, we identify hundreds of sequences conferring stabilization or destabilization upon mRNAs terminating downstream. One class of stabilizing element is a polyU sequence that can interact with poly(A) tails, inhibit the association of poly(A) binding protein, and confer increased stability upon introduction into ectopic transcripts. More generally, destabilization and stabilization elements are linked to the degree to which the poly(A) tail can engage in double-stranded structures. Isoforms engineered to fold into 3’ stem-loop structures not involving the poly(A) tail exhibit even longer half-lives. We suggest that double-stranded structures at the 3’ ends are a major determinant of mRNA stability. Half-lives of 21,248 mRNA 3’ isoforms in yeast were measured by rapidly depleting RNA polymerase II from the nucleus and performing direct RNA sequencing throughout the decay process.
Project description:We measured half-lives of 21,248 mRNA 3’ isoforms in yeast by rapidly depleting RNA polymerase II from the nucleus and performing direct RNA sequencing throughout the decay process. Interestingly, the half-lives of mRNA isoforms from the same gene, including nearly identical isoforms, often vary widely. Based on clusters of isoforms with different half-lives, we identify hundreds of sequences conferring stabilization or destabilization upon mRNAs terminating downstream. One class of stabilizing element is a polyU sequence that can interact with poly(A) tails, inhibit the association of poly(A) binding protein, and confer increased stability upon introduction into ectopic transcripts. More generally, destabilization and stabilization elements are linked to the degree to which the poly(A) tail can engage in double-stranded structures. Isoforms engineered to fold into 3’ stem-loop structures not involving the poly(A) tail exhibit even longer half-lives. We suggest that double-stranded structures at the 3’ ends are a major determinant of mRNA stability.
Project description:Gene expression analysis requires accurate measurements of global RNA degradation rates, earlier problematic with methods disruptive to cell physiology. Recently, metabolic RNA labeling emerged as an efficient and minimally invasive technique applied in mammalian cells. Here, we have adapted SH-Linked Alkylation for the Metabolic Sequencing of RNA (SLAM-Seq) for a global mRNA stability study in yeast using 4-thiouracil pulse-chase labeling. We assign high-confidence half-life estimates for 67.5 % of expressed ORFs, and measure a median half-life of 9.4 min. For mRNAs where half-life estimates exist in the literature, their ranking order was in good agreement with previous data, indicating that SLAM-Seq efficiently classifies stable and unstable transcripts. We then leveraged our yeast protocol to identify targets of the Nonsense-mediated decay (NMD) pathway by measuring the change in RNA half-lives; instead of steady-state RNA level changes. With SLAM-Seq, we assign 580 transcripts as putative NMD targets, based on their measured half-lives in wild-type and upf3Δ mutants. We find 225 novel targets, and observe a strong agreement with previous reports of NMD targets, 61.2 % of our candidates being identified in previous studies.This indicates that SLAM-Seq is a simpler and more economic method for global quantification of mRNA half-lives. Our adaptation for yeast yielded global quantitative measures of the NMD effect on transcript half-lives, high correlation with RNA half-lives measured previously with more technically challenging protocols, and identification of novel NMD regulated transcripts that escaped prior detection.
Project description:Purpose: Alternative polyadenylation (APA) can result in the generation of transcripts that terminate at different locations within the gene, which can result in different 3' UTRs. 3´ UTRs are known to contain RNA stabilizing and destabilizing motifs that provide a platform for binding of RNA binding proteins. Changes in 3´ UTRs for the different APA-generated isoforms of a gene could allow for inclusion or exclusion of these RNA stability elements. The goal of this study is determine the stability (half-lives based on transcript decay) of APA isoforms in proliferating and quiescent cells. Methods: The proliferating and quiescent (7-day contact inhibited) cells were treated with actinomycin D to stop transcription and the cells were harvested at different time points (0. 2, 4, 8 hours) for RNA isolation and global sequencing of 3´ ends. The adaptors and polyA sequenced were trimmed from each read. The reads were aligned to the human genome (hg19) using TopHat (v2.0.14). The aligned read files were used to determine the counts of APA isoforms of each gene using the code provided by Gruber et al. (PMID: 27382025). The counts of the APA isoforms were fit to an exponential decay model to obtain half-lives. The entire workflow was performed for two biological replicates: 12-1 and 12-3 strains of human dermal fibroblasts. Results: In two different fibroblast strains (12-1 and 12-3), we found that isoforms terminating at distal polyadenylation sites were more stable than isoforms terminating at proximal polyadenylation sites in quiescent, but not proliferating, fibroblasts. Conclusions: The transition from shorter to longer isoforms in quiescent cells is associated with stabilization of the transcripts.