Wounds in the embryo show a remarkable ability to heal quickly without leaving a
scar. Previous studies have found that an
actomyosin ring (purse string) forms around the
wound perimeter and contracts to close the
wound over the course of several dozens of minutes. Here, we report experiments that reveal an even faster mechanism which remarkably closes
wounds by more than 50% within the first 30s. Circular and elliptical
wounds (~100μm in size) were made in the blastoderm of early chick embryos and allowed to heal, with
wound area and shape characterized as functions of time. The closure rate displayed a biphasic behavior, with rapid constriction lasting about a minute, followed by a period of more gradual closure to complete healing. Fluorescent staining suggests that both healing phases are driven by
actomyosin contraction, with relatively rapid contraction of fibers at cell borders within a relatively thick ring of tissue (several cells wide) around the
wound followed by slower contraction of a thin supracellular
actomyosin ring along the margin, consistent with a purse string mechanism. Finite-
element modeling showed that this idea is biophysically plausible, with relatively isotropic contraction within the thick ring giving way to tangential contraction in the thin ring. In addition, consistent with experimental results, simulated elliptical
wounds heal with little change in aspect ratio, and decreased membrane tension can cause these
wounds to open briefly before going on to heal. These results provide new insight into the healing mechanism in embryonic epithelia.