Dcp1a, a novel Mek substrate, regulates the self-renewal and differentiation of mouse embryonic stem cells [Ribo-seq]

Mek inhibitor is widely applied to maintain pluripotency, while prolonged Mek inhibition compromises the developmental potential of mouse embryonic stem cells (ESCs). To better understand the mechanism of Mek in pluripotency maintenance, we first demonstrated that Mek regulates gene expression at post-transcriptional steps. Consistently, many of the 66 Mek substrates identified by quantitative phosphoproteomic analysis are involved in RNA processing. We further confirmed that S563 of Dcp1a, a mRNA decapping cofactor and P-body component, is phosphorylated by Mek1. Dcp1a, as well as two other P-body components Edc4 and Dcp2, are required for the proper self-renewal and differentiation of ESCs, indicating the role of P-bodies in ESCs. Dephosphorylation of Dcp1a S563 facilitates both self-renewal and differentiation of ESCs, through promoting P-body formation and RNA storage. In summary, our study identified 66 Mek substrates supporting the Erk-independent function of Mek, and revealed that Dcp1a, phosphorylated by Mek, regulates ESC self-renewal and differentiation, through modulating P-body formation. To demonstrate the role of Mek in post-transcriptional regulation of gene expression, ESCs were cultured with DMSO or 1 μM PD for 3 passages. Ribosome profiling was performed to validate DMSO or PD treated transripts translation rates.