Meeting Abstract
S3.1-1 Saturday, Jan. 4 08:00 Dynamics of Tissue Morphogenesis in Ascidians MUNRO, E.M.*; HASHIMOTO, H.; ROBIN, F.R.; SHERRARD, K.M.; University of Chicago; University of Chicago; University of Chicago; University of Chicago emunro@uchicago.edu
A key challenge in developmental biology is to understand how embryonic cells organize force production in space and time and how these forces are resolved into globally stereotyped patterns of cell shape change, rearrangement and tissue deformation. Ascidian embryos provide a unique opportunity to address this challenge; they elaborate all of the essential elements of the chordate body plan, but they do so in a few hours, with a few hundred large and optically clear cells, against the backdrop of highly stereotyped early cleavages and cell fate determination. In this talk, I will highlight our recent attempts to understand mechanisms that govern ascidian neurulation. The ascidian neural tube forms through neuroectoderm (Ne) invagination, followed by epidermal “zippering”, in which the neural folds and adjacent epidermis (Epi) meet at the midline, then exchange junctions in a posterior-anterior progression to separate the neural tube from the overlying epidermis. Using quantitative live imaging, we have identified a moving zone of actomyosin-dependent contractile activity just ahead of the zipper, in which individual Ne/Epi junctions sequentially undergo rapid shortening, drawing the zipper forward and drawing the edges of the neural plate into contact at the midline. Newly met epidermal cells remain associated with the zipper during Ne/Epi junctional exchange, elongate as the zipper moves anteriorly, then release from the zipper and relax towards more isodiametric shapes. Combining experimental manipulations with computer modeling, we have shown that a local increase in contractile tension within this zone provides the essential driving force, while junctional release and cell shape relaxation behind the zipper creates an essential mechanical asymmetry that leads to unidirectional zipper progression.
