Klf4 methylated by Prmt1 is required for lineage segregation of epiblast and primitive endoderm

The second cell fate decision in the early stage of mammalian embryonic development is pivotal; however, the underlying molecular mechanism is largely unexplored. Here, we report that Prmt1 acts as an important regulator in primitive endoderm (PrE) formation. First, an embryonic chimeric assay showed that Prmt1 inhibition induces the integration of mouse embryonic stem cells (ESCs) into the PrE. Second, Prmt1 inhibition promotes Gata6 expression in both mouse blastocysts and ESCs. Single-cell RNA sequencing and flow cytometry assays demonstrated that Prmt1 depletion in ESCs contributes to an emerging cluster, where PrE genes are upregulated significantly. Furthermore, the efficiency of extraembryonic endoderm stem cell induction increased in Prmt1-depleted ESCs. Finally, we showed that the pluripotency factor Klf4 methylated at Arg396 by Prmt1 is required for recruitment of the repressive mSin3a/HDAC complex to silence PrE genes. Therefore, we reveal a regulatory mechanism for cell fate decisions centered on Prmt1-mediated Klf4 methylation.