Meeting Abstract
P1.30 Monday, Jan. 4 A propagating zone of localized protrusive and contractile activity drives zippering and neural tube closure in ascidians. ROBIN, F.B.*; SHERRARD, K.M.; MONTGOMERY, M.; SEMON, S.; MUNRO, E.M.; University of Washington and University of Chicago; University of Washington and University of Chicago; University of Washington; University of Washington; University of Washington and University of Chicago rbfr@u.washington.edu
The ascidian neural tube forms by neurectoderm folding, followed by fusion of the neural folds at the dorsal midline by a posterior-to-anterior “zippering” process. Using time-lapse fluorescence microscopy, we found that neural closure is accompanied by the constriction of a supra-cellular purse string-like actin cable that develops at the boundaries between presumptive neurectoderm and lateral epidermis. Significantly, constriction of the purse string is strongly biased to it’s posterior end where it is accompanied by highly localized protrusive activity and cortical contractility. Immuno-staining of fixed embryos and time-lapse microscopy of live embryos revealed that the active RhoA and active forms of Myosin are similarly localized to the highly contractile posterior zone, which propagates posterior to anterior and cell to cell as zippering proceeds. Blocking the Rho-pathway kinase ROCK with the inhibitor Y-27632 leads to loss of localized activated Myosin and specifically causes the zipper to collapse and the entire purse string to relax. Following fusion of opposed neural fold cells, midline cells are first dragged anteriorly as the zipper progresses further forward, then abruptly released as the apical domains of presumptive dermal and neural cells lose contact. The result of this process is to form two epithelia (one neural, one dermal) from a single initial epithelial layer. Our data highlight the existence of a “morphogenetic organizer” that coordinates supercellular force generation in time and space to achieve the completion of an essential step in chordate development.
