Actin (white) accelerates toward a wound (bottom) over time (left to right)
Cells sustain rips and tears during processes such as migration. The plasma membrane is repaired within milliseconds, but resealing of the underlying actomyosin cortex can take several minutes. On page 785, Mandato and Bement investigate this process in frog oocytes and find that a polymerization zone and a contractile ring work together to close wounds.
Mandato and Bement find that the structure surrounding a wound is clearly contractile—square wounds round up, elongated wounds shorten fastest along their long axis, and rewounding causes nearby areas to spring open further. But contractility seems to be restricted to a narrow ring, whereas actin and myosin accumulate in a broader zone around this ring. Actin filaments can be tracked as they flow and accelerate into this zone, thus depleting the surrounding area. This process of cortical flow...