Ground-state pluripotent stem cells are characterized by Rac1-dependent Cadherin-enriched F-actin protrusions

Abstract

Pluripotent Stem Cells (PSCs) exhibit extraordinary differentiation potentials that can be propagated in vitro and thus are commonly utilized in regenerative medicine. While different types of PSCs exist which correspond to different stages of pluripotency during embryogenesis, important aspects of their biology in terms of their cellular architecture and mechanobiology have been less well understood, thereby limiting their tissue engineering application potentials. Since the actin cytoskeleton is a primary determinant of cell mechanical properties, here we sought to investigate how the actin cytoskeleton may be differentially regulated in different states of pluripotency. Comparing ground-state naive mESCs and the corresponding converted prime epiblast stem cells (EpiSCs), we observed the actin cytoskeleton is drastically reorganized during the naive to prime pluripotency transition. Strikingly, we reported a distinctive actin organization that appears to be unique to the ground state mESCs, whereby the isotropic cortical networks are decorated with prominent actin-enriched structures which contain cadherin-based cell-cell junctional components, despite not locating at cell-cell junctions. We termed these structures "cadheropodia" and showed they arise from the cis-association of E-cadherin extracellular domain. Our measurements revealed that cadheropodia is under low mechanical tension and exhibits minimal calcium dependence, consistent with its putative dependence on cis-interaction. Further, we identified Rac1 as a negative regulator of cadheropodia whereby active Rac1 induces its fragmentation and dissociation of {beta}-catenin. Taken together, we described a novel actin-based structures in the ground-state mESCs, which may have potential roles in ground-state pluripotency and serve as useful structural markers to distinguish heterogeneous population of pluripotent stem cells.