Decoupling the impact of microRNAs on translational repression versus RNA degradation in embryonic stem cells

ABSTRACT Translation and mRNA degradation are intimately connected, yet the mechanisms that regulate them are not fully understood. Here we studied the link between translation and mRNA stability in embryonic stem cells (ESCs). Transcripts showed a wide range of stabilities, which correlated with their translation levels. The protein DHH1 links translation to mRNA stability in yeast; however loss of the mammalian homolog, DDX6, in ESCs did not disrupt the correlation across transcripts. Instead, the loss of DDX6 led to upregulated translation of microRNA targets, without concurrent changes in mRNA stability. The Ddx6 knockout cells were phenotypically and molecularly similar to cells lacking all microRNAs ( Dgcr8 knockout ESCs). These data show that the loss of DDX6 can separate the two canonical functions of microRNAs: translational repression and transcript destabilization. Furthermore, these data uncover a central role for translational repression independent of transcript destabilization in defining the downstream consequences of microRNA loss.