Arp2/3 complex activity is necessary for mouse ESC differentiation, times formative pluripotency, and enables lineage specification

Abstract

SummaryMouse embryonic stem cells (mESCs), a model for differentiation into primed epiblast-like cells (EpiLCs), have revealed transcriptional and epigenetic control of early embryonic development. The control and significance of morphological changes, however, remain less defined. We show marked changes in morphology and actin architectures during differentiation that depend on Arp2/3 complex but not formin activity. Inhibiting Arp2/3 complex activity pharmacologically or genetically does not block exit from naive pluripotency but attenuates increases in EpiLC markers. We find that inhibiting Arp2/3 complex activity delays formative pluripotency and causes globally defective lineage specification as indicated by RNA-sequencing, with significant effects on TBX3-depedendent transcriptional programs. We also identify two previously unreported indicators of mESC differentiation; MRTF and FHL2, which have inverse Arp2/3 complex-dependent nuclear translocation. Our findings on Arp2/3 complex activity in differentiation and the established role of formins in EMT indicate that these two actin nucleators regulate distinct modes of epithelial plasticity.HighlightsArp2/3 complex activity is necessary for morphology changes during differentiationArp2/3 complex activity regulates transcriptional markers of differentiationInhibiting Arp2/3 complex activity delays entry into formative pluripotencyArp2/3 complex activity-dependent shuttling of FHL2 and MRTF occurs in mESCs

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

“…How this difference in YAP localization occurs between mouse and human is unknown, although a number of cytoskeletal factors regulate YAP localization, including stability of the actin cytoskeleton, contractility, and mechanical regulators such as ERM proteins 26 . Further highlighting differences between human and mouse ESCs, we recently reported that Arp2/3 complex activity is necessary for the differentiation of clonal mouse naïve ESCs to the primed epiblast state, which is in part mediated by translocation of myocardin-related transcription factor MRTF from the cytosol to the nucleus 38 . Additionally, a recent report suggests that Arp2/3 complex activity may form a positive feedback loop with YAP-TEAD1 transcriptional activity controlling cytoskeletal reorganization 39 ; thus Arp2/3 complex activity may regulate naïve pluripotency at multiple stages including initially to reorganize the actin cytoskeleton, but also during maintenance of naïve pluripotency through regulating YAP localization and hence activity.…”