P04. Dissecting the contribution of non-neural ectoderm to the vertebrate neural tube closure

Abstract

Neural tube closure is one of the most prominent morphogenetic events during vertebrate development with dynamic cell shape changes and reorganization of cells. These cell behaviors are observed not only in a forming neural tube (neural ectoderm) itself but also in epidermal (non-neural) ectoderm. Cells in the neural ectoderm undergo apical constriction and mediolateral intercalation, which allow the neural tissue to form a groove along the anteroposterior axis and converge toward the midline, respectively. Although the knowledge on cellular and molecular mechanisms within neural ectoderm during vertebrate neurulation is accumulating, contribution of non-neural ectoderm is not well understood. In tissue level, non-neural ectoderm intensively moves toward the dorsal side of the embryo, probably contributing to the actual closure event, and it has been shown by studies with chick embryos that explants of neural ectoderm isolated from non-neural ectoderm fail to form neural tube, demonstrating the importance of non-neural ectoderm for neural tube closure. To clarify cellular and molecular basis of non-neural ectoderm that contributes to neural tube closure, we have analyzed possible mechanisms that may generate a force causing the movements, using Xenopus laevis embryos as a vertebrate model system. We first tested a contribution of cell divisions by treating the embryos with hydroxyurea and aphidicolin (HUA), inhibitors for cell division, throughout neurulation. Time-lapse images and sections of fixed embryos revealed that neural tube closure of the HUA-treated embryos were indistinguishable from the untreated controls with cell divisions suppressed significantly, suggesting that cell divisions may be dispensable for the tube closure. We are currently examining other cellular mechanisms, including surface expansion, mediolateral and/or anteroposterior rearrangement, and radial intercalation of non-neural ectoderm cells, using digital scanned laser light sheet microscopy (DSLM) as one of powerful tools enabling live imaging of cell morphogenesis in neural tube closure.