GSE117121
To investigate the decay constants (half-lives) of transcript isoforms generated by alternative polyadenylation in proliferating and quiescent cells
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. Overall design: 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.