Apical constriction is a key cellular mechanism that drives morphogenetic processes such as gastrulation or neural tube closure. Although it is well established that polarised positioning and activation of actomyosin is crucial for apical constriction, the molecular factors that regulate this process in the context of vertebrate gastrulation are less clear. Now, Chenbei Chang and colleagues report that, in Xenopus, the RhoGEF protein Plekhg5 controls apical constriction of a group of cells on the embryo's surface that become bottle-shaped during gastrulation. The authors first show that plekhg5 mRNA localises to the blastopore lip and is able to induce ectopic bottle cells in a Rho-dependent manner when overexpressed. Apical localisation of the Plekhg5 protein in surface cells is dependent on its PH domain and GEF activity, and Plekhg5 expression promotes the apical enrichment of actomyosin and the elongation of bottle cells. Finally, the authors demonstrate that plekhg5 knockdown impairs blastopore lip formation and gastrulation movements and that plekhg5 acts downstream of nodal/activin signalling. Together, this work unravels how the localised expression of an actomyosin regulator drives apical constriction to ensure coordinated cell behaviours during gastrulation.
