Chick amniogenesis is mediated by an actin cable

This study examined the process of chick amniogenesis to determine whether the actin cable mechanism operating during amnion wound repair is a recapitulation of developmental events. Staining of the developing amnion with fluorescein isothiocyanate-labeled phalloidin indicated the presence of an actin cable in the amniotic head fold, which persisted through to the closure of the amnion. Transmission electron microscopy of the developing amnion revealed linearly arranged actin microfilaments in the elongated cells at the leading edge of the amnion, adjacent to either side of a nodule of numerous cells at the point of midline fusion. A mesh of cytoplasmic actin filaments was seen dispersed throughout the accumulated cells of the nodule. Lamellapodia were absent suggesting that cell crawling is not involved in amniogenesis. Addition of an enzyme inhibitor of Rho, cell-permeable C3 transferase, to the surface of the developing amnion prior to closure appeared to inhibit amniogenesis at the early embryonic stages.