Project Summary A fundamental question in cell biology is how the proper level of cell contractility is generated to drive cell and tissue morphogenesis. We know that cells must coordinate contractile events to enable dynamic movements. We do not know how they generate and tune contractility in the right place at the right time. Myosin 2 filaments are the dominant force-generating motor proteins in all cells and tissues. Recent advances in light microscopy have enabled us to observe myosin 2 dynamics in living cells at unprecedented spatial and temporal resolution. We have observed complexity at the subcellular level that we never considered or anticipated from decades of in vitro studies. This proposal uses high-resolution imaging along with a toolbox of cellular and molecular assays to dissect the mechanisms by which cells build actomyosin 2 contractile structures, tune them to fit the cellular process, and deconstruct them. Recent discoveries have clearly shown that after decades of investigation, myosin 2 is still holding secrets that we must uncover to fully understand cellular contractility. We anticipate the completion of this work will answer current questions and yield important new ones.