13-P084 Regulation of neural stem cells in the zebrafish hypothalamus by Shh

signaling to orchestrate cell shape changes during mesoderm invagination. The apically targeted transmembrane protein T48 acts as an anchor for RhoGEF2 via a PDZ binding motif and thereby ensures the apical enrichment of RhoGEF2 during mesoderm invagination allowing rapid and efficient ventral furrow formation. Apical constriction also requires the tethering of the contractile network to the adherens junctions. During gastrulation, the adherens junctions in the mesodermal cells are moved from a subapical localization to the apical end of the lateral membranes. We demonstrate that this movement is not simply mediated by a tensile force from constricting actin cytoskeleton, but an independent step of at least partial disassembly must occur which is controlled by Snail.