During embryogenesis, epithelial cell apical constriction (via actomyosin contraction) forces epithelial sheets to invaginate - a morphological change that can generate tissues with a complex architecture. Now, on , Nishimura and Takeichi report that Shroom3 (an actin-binding protein that regulates epithelial apical constriction) and Rho kinases [ROCKs; kinases that phosphorylate myosin regulatory light chain (MLC), leading to actomyosin contraction] interact to regulate epithelial sheet remodelling. The researchers show that in epithelial cells in vitro and in invaginating chick neural tube, Shroom3 binds to and recruits ROCKs to the epithelial apical junctions. They also show that the expression of RII-C1 (the Shroom3-binding site on ROCKs that they identify) or Shroom3 depletion removes apically localized ROCKs and blocks neural tube closure. Finally, epithelial cells in the closing neural plate have a planar-polarized distribution of phosphorylated MLC, they report, that is abolished by RII-C1 expression. This distribution might drive tube closure, suggest the researchers. Together,these results provide new insights into how epithelial sheets bend during embryogenesis.
