Reversal of morphogenesis in Hydra regeneration under external electric fields

Morphogenesis—the emergence of form and function in a developing animal, is one of the most remarkable examples of pattern formation in nature. The current picture of morphogenesis relies on biochemical patterning. However, morphogenesis results from the dynamic symbiotic interplay of three types of processes: biochemical, mechanical and electrical, spanning all scales from the molecular to the entire organism. One of the main challenges is to understand how living systems close the loop to stabilize the robust emergence of a viable body plan in development. The ability to modulate morphogenesis on demand will provide novel insights on this process. Towards this aim, we utilize Hydra regeneration and study morphogenesis under external AC electric fields. We demonstrate that an external electric field can be tuned to drive morphogenesis in Hydra regeneration, backward and forward, around a critical point in a controlled manner. Interestingly, a backward-forward cycle of morphogenesis leads to a newly emerged body plan in the re-developed folded tissue, which is not necessarily similar to the one before the reversal process. Thus, a controlled drive of morphogenesis allows in principle, multiple re-initiation of novel developmental trajectories for the same tissue. We will discuss the main experimental observations and their implications. Controlled reversal trajectories open a new vista on morphogenesis, painting it as a physical dynamic phase transition and call for a new theoretical framework for this phenomenon.