Lecturer:  Kinneret Keren, Department of Physics, Technion
Abstract:
We focus on the mechanical aspects of morphogenesis using Hydra, a small multicellular fresh-water animal, as a model system. Hydra has a simple body plan and is famous for its ability to regenerate an entire animal from small tissue pieces, providing a flexible platform to explore how mechanical forces and feedback contribute to the formation and stabilization of the body plan during morphogenesis. I will present our results showing that the nematic order of the supra-cellular muscle fibers in regenerating Hydra defines a coarse-grained field, whose dynamics provide an effective description of the morphogenesis process. Topological defects in the nematic order, which emerge early in the regeneration process, identify the sites where morphological features develop in the regenerating animal. We show that contractile activity in the muscle fibers leads to extensive, transient tissue deformations at these defect sites, suggesting that the nematic muscle fiber organization can act as a “mechanical morphogen” that provides local positional cues. I will further present our recent studies on the tissue mechanics and cellular dynamics underlying the elongation of regenerating Hydra along their future body axis as the tissue develops from a roughly round spheroid into a cylindrically shaped mature animal.  Overall our results indicate that that the nematic organization of the actomyosin cytoskeleton is an integral and important component of the morphogenesis process from the onset of Hydra regeneration.