The Dynamic Counterbalance of RAC1‐YAP/OB‐Cadherin Coordinates Tissue Spreading with Stem Cell Fate Patterning

Tissue spreading represents a key morphogenetic feature of embryonic development and regenerative medicine. However, how molecular signaling orchestrates the spreading dynamics and cell fate commitment of multicellular tissue remains poorly understood. Here, it is demonstrated that the dynamic counterbalance between RAC1–YAP and OB‐cadherin plays a key role in coordinating heterogeneous spreading dynamics with distinct cell fate patterning during collective spreading. The spatiotemporal evolution of individual stem cells in spheroids during collective spreading is mapped. Time‐lapse cell migratory trajectory analysis combined with in situ cellular biomechanics detection reveal heterogeneous patterns of collective spreading characteristics, where the cells at the periphery are faster, stiffer, and directional compared to those in the center of the spheroid. Single‐cell sequencing shows that the divergent spreading result in distinct cell fate patterning, where differentiation, proliferation, and metabolism are enhanced in peripheral cells. Molecular analysis demonstrates that the increased expression of RAC1–YAP rather than OB‐cadherin facilitated cell spreading and induced differentiation, and vice versa. The in vivo wound healing experiment confirms the functional role of RAC1–YAP signaling in tissue spreading. These findings shed light on the mechanism of tissue morphogenesis in the progression of development and provide a practical strategy for desirable regenerative therapies.