Saccharomyces Cerevisiae Modulates Cell Growth via Alternative Polyadenylation
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ABSTRACT: Dynamic 3' UTRs variation mediated by APA is one of the major determinants of post-transcriptional regulation. Though some progress has been made in understanding its function in mammalian cells, the role of APA in the model organism S. cerevisiae, which lack of miRNAs, is a matter of debate. Unlike mammalian cells, most of S. cerevisiae genes tend to express mRNAs with longer 3′ UTRs in proliferating cells. Further analysis demonstrated that 3' UTRs length and mRNA expression were negatively correlated in different growth conditions. By combining APA sequencing and polysome profiling, we observed that mRNA isoforms with shorter 3' UTRs with a higher translational efficiency in proliferating cells but not quiescent. Further analysis demonstrated that different function genes translational efficiency control by APA are differential modulated and closely related with growth conditions. Furthermore, we observed the correlation between asRNAs and translational efficiency of different length 3′ UTR transcripts, suggests asRNAs may involve in the regulation of translational efficiency mediated by APA. Thus, this study indicates conservation of molecular function of APA in different Eukaryotes, highlighting the importance of APA in regulating gene function.
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.
Project description:Alternative polyadenylation (APA) refers to the regulated selection of polyadenylation sites (PASs) in transcripts, which affects the length of their 3’ untranslated regions (3’UTRs). APA regulates stage- and tissue-specific gene expression by affecting the stability, subcellular localization or translation rate of transcripts. We have recently shown that SRSF3 and SRSF7, two closely related SR proteins, link APA to mRNA export. However, the underlying mechanism for APA regulation by SRSF3 and SRSF7 remained unknown. Here, we combined iCLIP and 3’-end sequencing to find that both proteins bind upstream of proximal PAS (pPAS), but exert opposing effects on 3’UTR length. We show that SRSF7 enhances pPAS usage in a splicing-independent and concentration-dependent manner by recruiting the cleavage factor FIP1, thereby generating short 3’UTRs. SRSF7-specific domains that are absent in SRSF3 are necessary and sufficient for FIP1 recruitment. SRSF3 promotes long 3’UTRs by maintaining high levels of the cleavage factor Im (CFIm) via alternative splicing. Using iCLIP, we show that CFIm binds before and after the pPASs of SRSF3 targets, which masks them and inhibits polyadenylation. In the absence of SRSF3, CFIm levels are strongly reduced, which exposes the pPASs and leads to shorter 3’UTRs. Conversely, during cellular differentiation, 3’UTRs are massively extended, while the levels of SRSF7 and FIP1 strongly decline. Altogether, our data suggest that SRSF7 acts as a sequence-specific enhancer of pPASs, while SRSF3 inhibits pPAS usage by controlling CFIm levels. Our data shed light on a long-standing puzzle of how one factor (CFIm) can inhibit and enhance PAS usage.
Project description:Most eukaryotic genes express alternative polyadenylation (APA) isoforms with different lengths of 3’ untranslated region (3’UTR). Here we show arsenic stress elicits global shortening of 3’UTRs through two mechanisms. First, stress leads to immediate shortening of 3’UTR due to preferential usage of proximal cleavage and polyadenylation sites (PASs), as revealed by 3’ end sequencing of newly made RNAs that are metabolically labeled with 4-thiouridine. Second, long 3’UTR isoforms are more rapidly degraded during recovery from stress as compared to short 3’UTR isoforms, further shortening 3’UTR lengths in the cell. Using ribonucleoprotein immunoprecipitation coupled with 3’ end sequencing (3’READS+RIP), we show that the RNA-binding protein T cell-restricted intracellular antigen-1 (Tia1) preferentially interacts with long 3’UTR isoforms via U-rich elements in alternative 3’UTR sequences, and the interaction correlates with stress granule (SG) association during stress and with mRNA decay during recovery from stress, indicating SG-mediated RNA clearance mechanism post stress. Importantly, genes whose 3’UTRs are shortened by APA during stress can evade stress-induced 3’UTR size-based mRNA degradation, leading to higher transcript abundance post stress. Moreover, proliferating and differentiated cells display different extents of 3’UTR shortening after stress, indicating cell type-specific of impact of stress on the 3’UTR landscape. Together, our data indicate that 3’UTR length plays important roles in gene expression in stressed cells, and APA functions as an adaptive stress response mechanism to preserve mRNAs.
Project description:Our ability to predict protein expression from DNA sequence alone remains poor, reflecting our limited understanding of cis-regulatory grammar and hampering the design of engineered genes for synthetic biology applications. Here, we generate a model that predicts the translational efficiency of the 5’ untranslated region (UTR) of mRNAs in the yeast Saccharomyces cerevisiae. We constructed a library of half a million 50-nucleotide- long random 5’ UTRs and assayed their activity in a massively parallel growth selection experiment. The resulting data allow us to quantify the impact on translation of Kozak sequence composition, upstream open reading frames (uORFs) and secondary structure. We trained a convolutional neural network (CNN) on the random library and showed that it performs well at predicting the translational efficiency of both a held-out set of the random 5’ UTRs as well as native S. cerevisiae 5’ UTRs. The model additionally was used to computationally evolve highly translating 5’ UTRs. We confirmed experimentally that the great majority of the evolved sequences lead to higher translation rates than the starting sequences, demonstrating the predictive power of this model. The sequences were assayed in the context of a constant promoter and downstream coding sequence. Cell growth was used as a proxy for protein expression. Growth was measured by determining the ratio of sequence counts before and after growth selection.
Project description:Alternative polyadenylation (APA) regulates mRNA translation, stability, and protein localization. However, it is unclear to what extent APA regulates these processes uniquely in specific cell types. Using a new technique, cTag-PAPERCLIP, we discovered significant differences in APA between the principal types of mouse cerebellar neurons, the Purkinje and granule cells, as well as between proliferating and differentiated granule cells. Transcripts that differed in APA in these comparisons were enriched in key neuronal functions and many differed in coding sequence in addition to 3’UTR length.
Project description:Alternative Cleavage and Polyadenylation (APA) often results in production of mRNA isoforms with either longer or shorter 3’UTRs from the same genetic locus, potentially impacting mRNA translation, localization and stability. Developmentally regulated APA can thus make major contributions to cell-type-specific gene expression programs as cells differentiate. During Drosophila spermatogenesis, approximately 500 genes undergo APA when proliferating spermatogonia differentiate into spermatocytes, producing transcripts with shortened 3’ UTRs, leading to profound stage-specific changes in the proteins expressed. The molecular mechanisms that specify usage of upstream polyadenylation sites in spermatocytes are thus key to understanding the changes in cell state. Here, we show that upregulation of PCF11 and Cbc, the two components of Cleavage Factor II (CFII), orchestrates APA during Drosophila spermatogenesis. Knock down of PCF11 or cbc in spermatocytes caused dysregulation of APA, with many transcripts normally cleaved at a proximal site in spermatocytes now cleaved at their distal site, as in spermatogonia. Forced overexpression of CFII components in spermatogonia switched cleavage of some transcripts to the proximal site normally used in spermatocytes. Our findings reveal a developmental mechanism where changes in expression of specific cleavage factors can direct cell-type-specific APA at selected genes.
Project description:Alternative Cleavage and Polyadenylation (APA) often results in production of mRNA isoforms with either longer or shorter 3’UTRs from the same genetic locus, potentially impacting mRNA translation, localization and stability. Developmentally regulated APA can thus make major contributions to cell-type-specific gene expression programs as cells differentiate. During Drosophila spermatogenesis, approximately 500 genes undergo APA when proliferating spermatogonia differentiate into spermatocytes, producing transcripts with shortened 3’ UTRs, leading to profound stage-specific changes in the proteins expressed. The molecular mechanisms that specify usage of upstream polyadenylation sites in spermatocytes are thus key to understanding the changes in cell state. Here, we show that upregulation of PCF11 and Cbc, the two components of Cleavage Factor II (CFII), orchestrates APA during Drosophila spermatogenesis. Knock down of PCF11 or cbc in spermatocytes caused dysregulation of APA, with many transcripts normally cleaved at a proximal site in spermatocytes now cleaved at their distal site, as in spermatogonia. Forced overexpression of CFII components in spermatogonia switched cleavage of some transcripts to the proximal site normally used in spermatocytes. Our findings reveal a developmental mechanism where changes in expression of specific cleavage factors can direct cell-type-specific APA at selected genes.
Project description:Alternative Cleavage and Polyadenylation (APA) often results in production of mRNA isoforms with either longer or shorter 3’UTRs from the same genetic locus, potentially impacting mRNA translation, localization and stability. Developmentally regulated APA can thus make major contributions to cell-type-specific gene expression programs as cells differentiate. During Drosophila spermatogenesis, approximately 500 genes undergo APA when proliferating spermatogonia differentiate into spermatocytes, producing transcripts with shortened 3’ UTRs, leading to profound stage-specific changes in the proteins expressed. The molecular mechanisms that specify usage of upstream polyadenylation sites in spermatocytes are thus key to understanding the changes in cell state. Here, we show that upregulation of PCF11 and Cbc, the two components of Cleavage Factor II (CFII), orchestrates APA during Drosophila spermatogenesis. Knock down of PCF11 or cbc in spermatocytes caused dysregulation of APA, with many transcripts normally cleaved at a proximal site in spermatocytes now cleaved at their distal site, as in spermatogonia. Forced overexpression of CFII components in spermatogonia switched cleavage of some transcripts to the proximal site normally used in spermatocytes. Our findings reveal a developmental mechanism where changes in expression of specific cleavage factors can direct cell-type-specific APA at selected genes.
Project description:Epithelial-mesenchymal transition (EMT) plays important roles in tumour progression and is orchestrated by dynamic changes in gene expression. While it is well established that post-transcriptional regulation plays a significant role in EMT, the extent of alternative polyadenylation (APA) during EMT has not yet been explored. Using 3’ end anchored RNA sequencing, we mapped the alternative polyadenylation landscape (APA) following TGF-β-mediated induction of EMT in human mammary epithelial cells and found APA generally causes 3’UTR lengthening during this cell state transition. Investigation of potential mediators of APA indicated the RNA-binding protein Quaking (QKI), a splicing factor induced during EMT, regulates a small subset of events including the length of its own transcript. Analysis of QKI CLIP-seq data identified the binding of QKI within 3’UTRs was enriched near cleavage and polyadenylation sites. Following QKI knockdown, APA of many transcripts are altered to produce predominantly shorter 3’UTRs associated with reduced gene expression. These findings reveal the changes in APA that occur during EMT and identify a potential role for QKI in this process.
Project description:Epithelial-mesenchymal transition (EMT) plays important roles in tumour progression and is orchestrated by dynamic changes in gene expression. While it is well established that post-transcriptional regulation plays a significant role in EMT, the extent of alternative polyadenylation (APA) during EMT has not yet been explored. Using 3’ end anchored RNA sequencing, we mapped the alternative polyadenylation landscape (APA) following TGF-β-mediated induction of EMT in human mammary epithelial cells and found APA generally causes 3’UTR lengthening during this cell state transition. Investigation of potential mediators of APA indicated the RNA-binding protein Quaking (QKI), a splicing factor induced during EMT, regulates a small subset of events including the length of its own transcript. Analysis of QKI CLIP-seq data identified the binding of QKI within 3’UTRs was enriched near cleavage and polyadenylation sites. Following QKI knockdown, APA of many transcripts are altered to produce predominantly shorter 3’UTRs associated with reduced gene expression. These findings reveal the changes in APA that occur during EMT and identify a potential role for QKI in this process.