Epithelial invagination, a common feature of embryogenesis, involves coordinated modulation of individual cell cytoskeletons. For example, during eye development, lens pit invagination, which is accompanied by a columnar-to-conical cell shape change (termed apical constriction, AC), is dependent on the cytoskeletal protein Shroom3. Now, through experiments in chick and mouse embryos and in MDCK cells, Richard Lang and colleagues provide new insights into how Shroom3 drives AC and lens invagination (see ). The researchers show that the activity of Rock1/2 (serine/threonine kinases that activate non-muscle myosin and that are activated by the Rho family GTPase RhoA) is required for lens invagination and that RhoA activity is required for Shroom3-induced AC. RhoA, when activated and targeted apically, is sufficient to induce AC, they report, and is essential for the apical localisation of Shroom3. Finally, they show that the RhoA guanine nucleotide exchange factor Trio is required for Shroom3-dependent AC. Thus, a Trio-RhoA-Shroom3 pathway is required for AC during lens pit invagination.
