Figure 1.

Halt and reversal of morphogenesis under external electric fields. (a) Possible trajectories for an incipient spheroid tissue under a field are shown. (b) Shown are images depicting the trajectory scheme in (a) top row: time (hour from tissue excising) and voltages (V_pp) for the images (from left): 5.5, 0; 42, 18; 68, 25.5; 97, 0. The red arrow represents the voltage is on, the black arrow represents V = 0. The voltage is switched off at 71 h. Scale bars, 100 μm. (c) Shown are images depicting the trajectory scheme in (a) bottom row: time (hour from tissue excising) and voltages (V_pp) for the images (from left): 2, 0; 53, 0; 80, 25; 108, 31; 136, 0. The voltage is switched off at 108 h. The red arrow represents the voltage is on, the black arrow represents V = 0. Scale bars, 100 μm. (d) Cumulative statistics for regeneration and reversal of morphogenesis are shown. The left panel shows cumulative statistics (147 tissue samples from 15 different experiments) exhibiting their first regeneration in the absence of an external voltage or a voltage below the critical value. Time is measured from the point of tissue excision, and regeneration is identified as the emergence of tentacles. All samples regenerated between 15 and 55 h, in agreement with previous results (31). The right panel shows cumulative statistics for reversal of morphogenesis, the folding back of fully regenerated Hydra into the incipient spheroid morphology, for 77 tissue samples (from 15 different experiments). All samples first regenerated into a mature Hydra. The folding time is estimated from the point at which the voltage was first set above 15 V_pp, the minimal voltage observed to affect morphology (e.g., shortening of the tentacles).