One of the most fascinating and important properties of living systems is their ability to cope with physical damage. This property is manifest in both single cells and multicellular systems, and is broadly conserved not only in a number of different animal phyla, but in plants as well. Because of its obvious clinical importance, multicellular wound healing has long been the subject of intense scrutiny. In contrast, repair of plasma membrane wounds in single cells has been overlooked until relatively recently. At least two mechanisms have been described: an extremely rapid membrane fusion event that provides an immediate block to the inrush of ions that would otherwise kill the cell, and a slower contractile response in which a circumferential ring of actin filaments and myosin-2 assembles around the wound and then closes. The primary goal of this project is to characterize the mechanisms that regulate assembly and closure of this ectopic contractile ring. Using Xenopus oocytes as a model system, a combination of physical, microscopic, and recombinant DNA-based approaches will be employed to test relationships between cell tension, local increases in rho class GTPase activity, and intracellular free calcium, in the recruitment of actin filaments and myosin-2 to the wound border. In addition to providing information directly relevant to the basic biological process of repair of damage to the plasma membrane, the proposed studies have the potential to provide insights into processes which resemble ectopic contractile ring assembly and closure, such as animal cell cytokinesis.