Meeting Abstract

16.3  Monday, Jan. 4  Neural Tube Closure: Zipper Propagation in Ascidian Embryos SEMON, Shelby N*; ROBIN, Francois; SHERRARD, Kristin; MUNRO, Edwin; Univ. of Washington, Seattle; MGCB, Univ. of Chicago; The Center for Cellular Dynamics; MGCB, Univ. of Chicago snsemon@u.washington.edu

Ascidians are a member of the chordate phylum and as such they undergo many of the same developmental processes that other chordates undergo. The difference is that Ascidians have a much smaller number of cells and larger cell size to embryo size ratio making them an ideal system in which to study the fundamental processes involved in neural tube closure. Focusing on the cellular processes involved in neural tube closure, we used confocal microscopes for fixed and time lapse imaging with fluorescent probes to carefully observe the cellular behaviors of control embryos. We found that neural tube closure proceeds unidirectionally from posterior to anterior in a behavior we call zippering. This behavior involves three main processes: cell crawling, adhesion and contraction. Focusing on the role of contractility, we found that there is a mechanically continuous actin purse string that has myosin localized in an area of high contractility in the boundary cells closest to the zipper. Using Y-27632, a drug that inhibits RhoKinase-activated myosin to inhibit contractility at different stages during zipper closure, we found that when Y-27632 was added near the beginning of the zippering process, zippering did not proceed and when added late in the zippering process, the zipper broke and the interior structures of the embryo extended out of the anterior half. However, invagination of the floor cells of the neural plate occurred normally in Y-27632 treated embryos. We conclude that contractility is essential for zipper initiation and propagation but not a driving force in the invagination that proceeds the zippering process.