Arp2/3 Complex Activity Enables Nuclear YAP for Naive Pluripotency of Human Embryonic Stem Cells

Our understanding of transitions of human embryonic stem cells between distinct stages of pluripotency relies predominantly on regulation by transcriptional and epigenetic programs with limited insight on the role of established morphological changes. We report remodeling of the actin cytoskeleton of human embryonic stem cells (hESCs) as they transition from primed to naive pluripotency that includes assembly of a ring of contractile actin filaments encapsulating colonies of naive hESCs. Activity of the Arp2/3 complex is required for the actin ring, uniform cell mechanics within naive colonies, nuclear translocation of the Hippo pathway effectors YAP and TAZ, and effective transition to naive pluripotency. RNA-sequencing analysis confirms that Arp2/3 complex activity regulates Hippo signaling in hESCs, and impaired naive pluripotency with inhibited Arp2/3 complex activity is rescued by expressing a constitutively active, nuclear-localized YAP-S127A. These new findings on the cell biology of hESCs reveal a mechanism for cytoskeletal dynamics coordinating cell mechanics to regulate gene expression and facilitate transitions between pluripotency states.