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

Pluripotent Stem Cells (PSCs) exhibit extraordinary differentiation potential and are thus highly valuable cellular model systems. However, while different PSC types corresponding to distinct stages of embryogenesis have been in common use, aspects of their cellular architecture and mechanobiology remain insufficiently understood. Here we investigated how the actin cytoskeleton is regulated in different pluripotency states. We observed a drastic reorganization during the transition from ground-state naïve mouse embryonic stem cells (mESCs) to converted prime epiblast stem cells (EpiSCs). mESCs are characterized by prominent actin-enriched cortical structures that contain cadherin-based cell-cell junctional components, despite not locating at cell-cell junctions. We termed these structures "Non-Junctional Cadherin Complexes (NJCC)" and showed that they are under low mechanical tension, depend on the ectodomain but not the cytoplasmic domain of E-cadherin, and exhibit minimal calcium dependence. Active Rac1 was identified as a negative regulator that promotes β-catenin dissociation and NJCC fragmentation. Our data suggests that NJCC may arise from the cis-association of E-cadherin ectodomain, with potential roles in ground-state pluripotency, and could serve as structural markers to distinguish heterogeneous population of pluripotent stem cells.