Anisotropic Cell Shape and Motion Coordinate Hindbrain Neuropore Morphogenesis.

Neural tube closure is a critical morphogenetic process in vertebrate development, and failure to close cranial regions such as the hindbrain neuropore (HNP) leads to severe congenital malformations. While mechanical forces like actomyosin purse-string contraction and directional cell crawling have been implicated in driving HNP closure, how these forces organize local cell shape and motion to produce large-scale tissue remodeling remains poorly understood. Using live and fixed imaging of mouse embryos combined with cell-based biophysical modeling, we show that these force-generating mechanisms are insufficient to explain the robust patterns of cell elongation and nematic alignment observed at the HNP border. Instead, we show that local anisotropic stress and cytoskeletal organization are required to generate these patterns and promote midline cell motion. Our model captures key features of cell shape dynamics and emergent nematic order, which we confirm experimentally, including the alignment of actin fibers with cell shape and enhanced midline cell speed. Comparative analysis with chick embryos, which lack supracellular purse-strings, supports a conserved link between tension generation and cellular patterning. These findings establish a physical framework connecting force generation, cell shape anisotropy, and tissue morphodynamics during epithelial gap closure.