Dynamin regulates epithelial maintenance and apical constriction in epithelial monolayers
Apical constriction converts the shape of a polarized epithelial cell from a tall column into an inverted cone. This morphological process is requisite to the bending of epithelial monolayers observed during gastrulation, neural tube formation and the patterning of tubular organs such as the mammary gland, kidney and lung. Apical constriction is an effect of the acto-myosin contractile system remodeling at the apical junctional region. One molecule that has the ability to regulate actin is dynamin. This mechanoenzyme is known for its function in deforming membranes during endocytosis and for its dependence on GTP binding and hydrolysis to perform this function. Here, we use imaging approaches to probe dynamin’s role in actin remodeling leading to apical constriction. We show that expression of a nucleotide free or GDP-bound form of dynamin (ie. Dyn2K44A), but not GTP-bound forms or other general endocytic inhibitors, leads to dramatic apical constriction of expressing cells in the MDCKII epithelial monolayer. This is dependent on dynamin’s localization at the apical junctional region and on the activity of Rho-kinase (ROCK), but not of Myosin Light Chain Kinase (MLCK), to stimulate myosin IIB. A direct interaction of the nucleotide free/GDP-bound form of dynamin with cortactin is necessary to induce apical constriction, but this is independent of cortactin’s interaction with Arp2/3 and N-WASP. Instead, cortactin’s role may relate to its ability to directly bind to actin. Our findings thus reveal that dynamin and cortactin play important roles in controlling acto-myosin-based apical constriction in polarized epithelial cells by orchestrating actin assembly and restructuring within these cells.