Fig. 7.

A Trio-RhoA-Shroom3 pathway is required for apical constriction during lens pit invagination. Model depicting the proposed molecular pathway by which lens pit cell apical constriction drives invagination. Pax6 and RhoA regulate Shroom3 expression and apical localization, respectively. The Shroom3-dependent apical constriction machinery requires Trio activation of RhoA. This leads to activation of the contractile, actin-myosin network and a reduced apical circumference of cells. The coordinated action of a localized group of cells that are apically constricting causes inward bending and invagination of the epithelial placode forming the lens pit.