Wound-induced assembly and closure of an actomyosin purse string in Xenopus oocytes

Background: Both single cells and multicellular systems rapidly heal physic al insults but are thought to do so by distinctly different mechanisms. Wou nds in single cells heal by calcium-dependent membrane fusion, whereas mult icellular wounds heal by a variety of different mechanisms, including circu mferential contraction of an actomyosin 'purse string' that assembles aroun d wound borders and is dependent upon the small GTPase Rho. Results: We investigated healing of puncture wounds made in Xenopus oocytes , a single-cell system. Oocyte wounds rapidly assumed a circular morphology and constricted circumferentially, coincident with the recruitment of fila mentous actin (F-actin) and myosin-ll to the wound borders. Surprisingly, r ecruitment of myosin-ll to wound borders occurred before that of F-actin, F urther, experimental disruption of F-actin prevented healing but did not pr event myosin-ll recruitment. Actomyosin purse-string assembly and closure w as dependent on Rho GTPases and extracellular calcium. Wounding resulted in reorganization of microtubules into an array similar to that which forms d uring cytokinesis in Xenopus embryos. Experimental perturbation of oocyte m icrotubules before wounding inhibited actomyosin recruitment and wound clos ure, whereas depolymerization of microtubules after wounding accelerated wo und closure. Conclusions: We conclude the following: actomyosin purse strings can close single-cell wounds; myosin-ll is recruited to wound borders independently o f F-actin; purse-string assembly is dependent on a Rho GTPase; and purse-st ring assembly and closure are controlled by microtubules. More generally, t he results indicate that actomyosin purse strings have been co-opted throug h evolution to dispatch a broad variety of single-cell and multicellular pr ocesses, including wound healing, cytokinesis and morphogenesis.