Meeting Abstract
P1.29 Monday, Jan. 4 CellularBasis for Ascidian Neurulation SHERRARD, K.*; ROBIN, F; CARVAJAL, D.; DANAHER, B.; DENG, W.; JOSHI, S.; MONTGOMERY, M.; SEMON, S.; WHITE, D.; MUNRO, E.; Center for Cell Dynamics, University of Washington; Center for Cell Dynamics (U.W.) and University of Chicago; Universidad de Antioquia, Columbia; Center for Cell Dynamics, University of Washington; SARS Institute, Bergen, Norway; University of Pittsburgh; University of Washington; University of Washington; University of Alberta, Edmonton; Center for Cell Dynamics (U.W.) and University of Chicago kmsherra@alumni.uchicago.edu
Ascidians form a neural tube of only a few hundred cells, providing an unparalleled opportunity to study this fundamental morphogenetic process at the cellular level. Several distinct subprocesses contribute to ascidian neurulation. First, primary invagination of the neural plate is followed by axial elongation accompanied by mediolateral cell-cell intercalation and oriented cell divisions. Second and concurrently, constriction of the blastopore and medially-directed crawling bring epidermal cells together at the posterior midline to initiate neural tube closure. Finally, neural tube closure proceeds through anterior to posterior zippering of both the neural tube and the overlying epidermal cells. Experiments with explants and laser ablation reveal that neural plate invagination proceeds normally in the absence of the posterior zipper-forming cells, but zippering fails. Conversely, zipper initiation and propagation proceed normally in the absence of the primary neural plate. Furthermore, unlike in vertebrates, formation and elongation of the neural tube does not require the presence of a notochord. A propagating zone of localized rho-kinase-dependent myosin activation is required for blastopore closure and for zippering, but not for invagination of the neural plate. Thus in ascidians, the complex process of neurulation can be decomposed into, and understood in terms of, a set of fundamental cellular mechanisms that are directly amenable to experimental analysis.
