Hydra Regeneration and the Physics of Morphogenesis

Morphogenesis, the emergence of functional form in a developing organism, is one of the most remarkable examples of pattern formation in nature. Despite substantial progress, we still do not understand the organizational principles underlying the convergence of this process, across scales, to form viable organisms under variable conditions. 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 recent results showing that the nematic order of the supra-cellular actin fibers in regenerating Hydra defines a coarse-grained field, whose dynamics provide an effective description of the morphogenesis process. In particular, I will show that topological defects in the nematic order of the actin fibers act as organization centers of the morphogenesis process, with the main morphological features developing at defect sites. Finally, we aim to directly demonstrate that mechanical constraints can pattern the body plan during morphogenesis via mechanical feedback and I will describe our progress in this direction.