Canalized morphogenesis driven by inherited tissue asymmetries in Hydra regeneration

The emergence of a body axis is a central step in animal morphogenesis. In many cases, the animal’s body axis provides two separate guides for establishing the basic layout of the developing body plan: a symmetry axis and a polar direction. We take advantage of the relatively simple body plan of the freshwater animal Hydra to separate these two features of the body axis and focus on the emergence of polarity along a developmental trajectory. In this talk, I will present our work on regenerating tissue strips which fold into hollow spheroids by adhering their distal ends of opposite original polarities, and hence serve as frustrating initial conditions where the polarity cannot be trivially preserved. Despite the convoluted folding process and the tissue rearrangements during regeneration, these tissue strips develop in a reproducible manner, preserving the original polarity and yielding an ordered body plan. These observations suggest that the integration of mechanical and biochemical processes supported by their mutual feedback attracts the tissue dynamics towards a well-defined developmental trajectory. Hydra thus provide an example of dynamic canalization in which the dynamic rules are instilled, but, in contrast to the classical picture, the detailed developmental trajectory does not unfold in a programmatic manner