This proposal focuses on dissecting of the molecular mechanisms involved in the control of cell division, cell polarization, and morphogenesis. These simultaneously interrelated and functionally distinct processes are controlled by small GTPases, switch like proteins that primarily act at cell membranes to remodel cellular physiology. These proteins perform numerous functions in cells and tissues and their activity is highly regulated. We propose to study the role of several small GTPases during these processes in intact model organisms, including the nematode C. elegans and the fruit fly, Drosophila using a combination of live cell imaging, classical genetics, and optogenetics. We will also dissect the mechanisms responsible for the spatial and temporal activation of these GTPases which is critical for cell division, cell polarization, and morphogenesis. Given the high degree of conservation of these processes, information gained in this project could aid our understanding of certain cancers and the origin of some birth defects.