The RhoGEF protein Plekhg5 regulates medioapical actomyosin dynamics of apical constriction during Xenopus gastrulation

Apical constriction results in apical surface reduction in epithelial cells and is a widely used mechanism for epithelial morphogenesis during embryo development. Both medioapical and junctional actomyosin remodeling are involved in apical constriction, but the deployment of medial versus junctional actomyosin in specific developmental processes has not been fully described. Additionally, genetic regulation of actomyosin dynamics during apical constriction is poorly understood in vertebrate systems. In this study, we investigate actomyosin dynamics and their regulation by the RhoGEF protein Plekhg5 in Xenopus bottle cells. Using live imaging and quantitative image analysis, we show that bottle cells assume different shapes, with rounding bottle cells constricting earlier in small clusters followed by fusiform bottle cells forming between the clusters. Though both medioapical and junctional actomyosin accumulate as surface area decreases, apical constriction is better correlated with medioapical actomyosin localization, which may promote formation of microvilli in the apical membrane. Knockdown of plekhg5 disrupts both medioapical actomyosin activity and apical constriction but does not affect initial F-actin dynamics. Taken together, our study reveals distinct cell morphologies, uncovers actomyosin behaviors, and demonstrates the crucial role of a RhoGEF protein in controlling actomyosin dynamics during apical constriction of bottle cells in Xenopus gastrulation.