Meeting Abstract

16.4  Monday, Jan. 4  Initiation of Neural Tube Closure in Ciona Intestinalis MONTGOMERY, M.S.*; MUNRO, E.; SHERRARD, K.; ROBIN, F.; Univ. of Washington, Seattle; Univ. of Washington, Seattle; Univ. of Washington, Seattle; Univ. of Washington, Seattle monicm2@u.washington.edu

Ascidian neural tube closure (zippering) is initiated by the assembling of cells and materials at a posteriorly located center we are calling the zipper origin. The zipper origin as a structure has not previously been described in the literature. To advance our understanding of the prospective identity and morphological change of cells in contact with the zipper origin, we created 3-D reconstructions through Amira and 3-D Virtual Embryo of early neurula we fixed and stained in phalloidin. We find that posterior-most muscle, neural plate, notochord, and epidermal cells meet as they extend towards the zipper origin. With time-lapse imaging and confocal microscopy, we show that initiation of neural tube closure occurs by three main events: 1) cinching of the apical ends of muscle cells lining the closing blastopore; 2) rolling-inward of the two posterior-most roof cells; and 3) crawling of posterior epithelial cells towards the zipper origin. We provide evidence that this gathering at the zipper origin is significantly driven by myosin contractility. We find the presence of monophosphorylated nonmuscle myosin II at the same time and location of blastopore closure and building of the zipper origin. We also find diphosphorylated nonmuscle myosin II concentrated at the zipper origin at earlier and later stages corresponding to the time of initiation of neural tube closure. We show further that inhibition of nonmuscle myosin II through the Rho kinase pathway causes a drastic disassembly of material already collected at the zipper origin and significant deformation of zipper-initiating cells. Our results show that activation of Rho kinase and myosin II is necessary to initiate tube closure. With reduced myosin contractility, formation of the neural tube does not occur, indicating the motor protein’s role as an indispensable biomechanical device.