MicroRNAs control the apoptotic threshold in primed pluripotent stem cells through regulation of BIM

Mammalian primed pluripotent stem cells have been shown to be highly susceptible to cell death stimuli due to their low apoptotic threshold, but how this threshold is regulated remains largely unknown. Here we identify miRNA-mediated regulation as a key mechanism controlling apoptosis in the post-implantation epiblast. Moreover, we find that three miRNA families, miR-20, miR-92 and miR-302, control the mitochondrial apoptotic machinery by fine-tuning the levels of expression of the pro-apoptotic protein BIM. These families therefore represent an essential buffer needed to maintain cell survival in stem cells that are not only primed for differentiation but also for cell death. We used microarrays to compare the gene expression profiles of Dicer conditional Epiblast stem cells (Dicer fx/fx EpiSCs, used as control cells) and Dicer deleted epiblast stem cells (Dicer-/- EpiSCs) five days after the induction of Dicer deletion Dicer fx/fx EpiSCs were left untreated (control cells) or treated with 0.3uM of 4-OH-Tamoxifen for three days and without Tamoxifen for two further days, until day 5 when RNA was extracted and used for microarray analysis. Three independent deletion experiments including a Dicer fx/fx sample and a Dicer -/- sample were analyzed as biological replicates.