Shroom3-mediated recruitment of Rho kinases to the apical cell junctions regulates epithelial and neuroepithelial planar remodeling

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Abstract
Remodeling of epithelial sheets plays important roles in animal morphogenesis. Shroom3 is known to regulate the apical constriction of epithelial cells. Here, we show that Shroom3 binds ROCKs and recruits them to the epithelial apical junctions. We identified the Shroom3-binding site (RII-C1) on ROCKs, and found that RII-C1 could antagonize the Shroom3-ROCK interaction, interfering with the action of Shroom3 on cell morphology. In the invaginating neural plate/tube, Shroom3 colocalized with ROCKs at the apical junctions; Shroom3 depletion or RII-C1 expression in the tube removed these apically localized ROCKs, and concomitantly blocked neural tube closure. Closing neural plate exhibited peculiar cell assemblies, including rosette formation, as well as a planar-polarized distribution of phosphorylated myosin regulatory light chain, but these were abolished by ROCK inhibition or RII-C1 expression. These results demonstrate that the Shroom3-ROCK interaction is crucial for the regulation of epithelial and neuroepithelial cell arrangement and remodeling.