The RhoGEF protein Plekhg5 regulates apical constriction of bottle cells during gastrulation.

Apical constriction regulates epithelial morphogenesis during embryonic development, but how this process is controlled is not understood completely. Here, we identify a Rho guanine nucleotide exchange factor (GEF) gene as an essential regulator of apical constriction of bottle cells during gastrulation. is expressed in the blastopore lip and its expression is sufficient to induce ectopic bottle cells in epithelia of different germ layers in a Rho-dependent manner. This activity is not shared by , which encodes another organizer-specific RhoGEF. Plekhg5 protein is localized in the apical cell cortex via its pleckstrin homology domain, and the GEF activity enhances its apical recruitment. Plekhg5 induces apical actomyosin accumulation and cell elongation. Knockdown of inhibits activin-induced bottle cell formation and endogenous blastopore lip formation in gastrulating frog embryos. Apical accumulation of actomyosin, apical constriction and bottle cell formation fail to occur in these embryos. Taken together, our data indicate that transcriptional regulation of expression at the blastopore lip determines bottle cell morphology via local polarized activation of Rho by Plekhg5, which stimulates apical actomyosin activity to induce apical constriction.