A microtubule‐LUZP1 association around tight junction promotes epithelial cell apical constriction

Apical constriction is critical for epithelial morphogenesis, including neural tube formation. Vertebrate apical constriction is induced by di‐phosphorylated myosin light chain (ppMLC)‐driven contraction of actomyosin‐based circumferential rings (CRs), also known as perijunctional actomyosin rings, around apical junctional complexes (AJCs), mainly consisting of tight junctions (TJs) and adherens junctions (AJs). Here, we revealed a ppMLC‐triggered system at TJ‐associated CRs for vertebrate apical constriction involving microtubules, LUZP1, and myosin phosphatase. We first identified LUZP1 via unbiased screening of microtubule‐associated proteins in the AJC‐enriched fraction. In cultured epithelial cells, LUZP1 was found localized at TJ‐, but not at AJ‐, associated CRs, and LUZP1 knockout resulted in apical constriction defects with a significant reduction in ppMLC levels within CRs. A series of assays revealed that ppMLC promotes the recruitment of LUZP1 to TJ‐associated CRs, where LUZP1 spatiotemporally inhibits myosin phosphatase in a microtubule‐facilitated manner. Our results uncovered a hitherto unknown microtubule‐LUZP1 association at TJ‐associated CRs that inhibits myosin phosphatase, contributing significantly to the understanding of vertebrate apical constriction. Synopsis Apical cell constriction drives epithelial morphogenesis and is mediated by junctional actomyosin ring constriction in vertebrates. Here, the leucine zipper motif‐containing protein LUZP1 is found as a new regulator of this process via inhibition of myosin phosphatase activity at tight junction (TJ)‐associated circumferential rings (CRs). The microtubule‐associated protein LUZP1 localizes at TJ‐associated CRs. Di‐phosphorylated myosin light chain (ppMLC) promotes recruitment of LUZP1 to TJ‐associated CRs. LUZP1 inhibits myosin phosphatase to increase myosin light chain phosphorylation and promote CR contraction during apical constriction. Microtubules facilitate LUZP1‐mediated inhibition of myosin phosphatase activity. Graphical Abstract The neural tube‐closure regulator LUZP1 drives apical constriction of epithelial cells by inhibiting myosin phosphatase activity in a microtubule‐dependent manner