Contraction and polymerization cooperate to assemble and close actomyosin rings around Xenopus oocyte wounds

Xenopus oocytes assemble an array of F-actin and myosin 2 around plasma mem brane wounds. We analyzed this process in living oocytes using confocal tim e-lapse (four-dimensional) microscopy. Closure of wounds requires assembly and contraction of a classic "contractile ring" composed of F-actin and myo sin 2. However, this ring works in concert with a 5-10-mum wide "zone" of l ocalized actin and myosin 2 assembly. The zone forms before the ring and ca n be uncoupled from the ring by inhibition of cortical flow and contractili ty. However, contractility and the contractile ring are required for the st ability and forward movement of the zone, as revealed by changes in zone dy namics after disruption of contractility and flow, or experimentally induce d breakage of the contractile ring. We conclude that wound-induced contract ile arrays are provided with their characteristic flexibility, speed, and s trength by the combined input of two distinct components: a highly dynamic zone in which myosin 2 and actin preferentially assemble, and a stable cont ractile actomyosin ring.