show Abstracthide AbstractNaïve and primed pluripotent states retain distinct molecular properties, yet limited knowledge exists on how their state transitions are regulated. Here we identify Mettl3, an N6-Methyladenosine (m6A) transferase, as a regulator for terminating murine naïve pluripotency. Mettl3 knockout pre-implantation epiblasts and naïve embryonic stem cells (ESCs) are depleted for m6A in mRNAs and yet, are viable. However, they fail to adequately terminate their naïve state, and subsequently undergo aberrant and restricted lineage priming at the post-implantation stage, leading to early embryonic lethality. m6A predominantly and directly reduces mRNA stability, including that of key naïve pluripotency promoting transcripts. This study highlights a critical role for an mRNA epigenetic modification in vivo, and identifies regulatory modules that functionally influence naïve and primed pluripotency in an opposing manner. Overall design: m6A-seq was measured from total RNA in mouse embryonic stem cells (ESCs), embroid bodies (EBs) and embronic fibroblasts (MEF). 3 biological replicates are available from BVSC ESC line and EBs, and two biological replicates are available for MEFs. m6A-seq was also measured from total RNA in Mettl3 knockout ESCs. Each sample consist of IP to m6A and control input.