  Morphogenesis involves the dynamic interplay of biochemical, mechanical and
electrical processes. Here we ask: to what extent can the course of
morphogenesis be modulated and controlled by an external electric field? We
show that above a critical amplitude, an external electric field can halt
morphogenesis in Hydra regeneration. Moreover, above this critical amplitude,
the electric field can even lead to reversal dynamics: a fully developed Hydra
folds back into its incipient spheroid morphology. The potential to renew
morphogenesis is re-exposed when the field is reduced back to amplitudes below
criticality. These dynamics are accompanied by modulations of the Wnt3
activity, a central component of the head organizer in Hydra. Reversal of
morphogenesis is shown to be triggered by enhanced epithelial electrical
excitations, accompanied by intensified calcium activity, indicating that
electrical processes play an instructive role to a level that can direct
developmental trajectories. Reversal of morphogenesis by external fields, calls
for extending its framework beyond programmatic, forward-driven, hierarchical
processes.
