Naive pluripotent cells can be stimulated to transition into a primed state that readies them for further differentiation. Yet, the molecular bases for maintenance of pluripotent states and the signaling pathways that govern the transition between them remain relatively unexplored. To gain further insight into these processes, Geula et al. screened a library of siRNAs targeting genes with potential roles in pluripotency reprogramming of mouse embryonic stem cells (mESCs). A number of epigenetic regulators, including proteins in the polycomb complex, were identified along with Mettl3, a protein that collaborates with Mettl14 as part of the machinery that installs N6-methyladenosine (m6A) modifications in mRNA. To explore the function of Mettl3 and m6A modification in pluripotency and differentiation, the authors generated a targeted knockout of Mettl3 in mice and derived ESCs from these animals. Knockout mESCs sustained a naive pluripotent state in which pathways involved in priming and differentiation are blunted. MS analysis revealed that mRNAs from the knockout mESCs have fewer m6A marks relative to wild-type ESCs, and RNA-seq profiling of m6A modifications across developmental stages showed that Mettl3 and m6A depletion directly enhanced the stability of mRNAs for genes that maintain naive pluripotency. Ribosome profiling analysis confirmed that the resultant elevated protein levels were not directly related to the depletion in m6A methylation on mRNA transcripts. Taken together, the results support the idea that m6A modification of mRNA has an important regulatory role in the orderly transition between naive and primed pluripotent states and highlight the need for a deeper understanding of the machineries that write, erase and read these RNA epigenetic marks.
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Sheppard, T. m6A partial differential. Nat Chem Biol 11, 175 (2015). https://doi.org/10.1038/nchembio.1764