Project Summary Mechanical Regulation of Cell Adhesion by Dynamic Cytoskeletal Assemblies Epithelial tissue is built by dynamic adhesions, cell-cell junctions, that connect neighboring cells to maintain tissue cohesion and barrier function yet also allow dynamic processes like wound healing and tissue morphogenesis. Contractile forces generated within the actomyosin cytoskeleton are transmitted to cell-cell junctions to control the local cell shape and motions that sculpt tissue morphogenesis and initiate downstream signaling pathways that control cell fate. Understanding how the biophysical properties of cell-cell junctions are regulated has widespread implications for understanding and treating defects during embryonic development, for tissue engineering and the diagnosis and treatment of metastatic tumors. This proposal leverages innovative combination of cell biophysics, molecular cell biology, live cell imaging, mathematical modeling and optogenetics to investigate how RhoA signals regulate contractile forces to drive changes in cell-cell junction length that control cell shape and, ultimately, tissue morphogenesis. We propose experiments to elucidate how force-dependent process regulating actomyosin contractility, membrane remodeling and RhoA signaling feedback to each other to control junction length and length changes. We approach this problem by integrating molecular cell biology approaches with advanced quantitative imaging of cytoskeletal dynamics and biophysical measurements. By obtaining kinetic and kinematic (motion) signatures of proteins at varying levels of tension, we identify mechanisms of force transmission within focal adhesions and the actin cytoskeleton. We then collaborate closely with theoretical physicists to test the predictions of analytical theory and simulations with our quantitative biophysical measurements. This work builds a biophysical understanding of cell adhesion, tension and shape that, ultimately, will provide the framework for theories and models of tissue morphogenesis that will have predictive power in understanding in complex physiological processes. More generally, the strategies developed in this proposal can be applied more generally to understand how force-sensitive feedbacks within the cytoskeletal conspire to facilitate cell morphogenic processes. This will enable the development of improved therapies to treat diseases involved in tissue homeostasis that currently remain elusive by solely treating molecular targets.