Genetic analysis of developmental mechanisms in hydra. XIX. Stimulation of regeneration by injury in the regeneration-deficient mutant strain, reg-16.

A mutant strain of Hydra magnipapillata, reg-16, has a very low regenerative capacity. After head removal, it usually restores 10-20% of the original number of tentacles in 7 days. A procedure was found to markedly improve tentacle regeneration in this strain. The closed wound located at the apical regenerating tip of the decapitated polyp was gently reopened using a pair of forceps. Reg-16 polyps treated in this way at 24 and 48 h after head removal restored nearly all of the original number of tentacles in 7 days. A lateral tissue transplantation procedure was employed to examine the effect of wound reopening on the morphogenetic potential of decapitated reg-16 polyps. Wound reopening produced a significant increase in head activation level without producing a preceding decrease in head inhibition level. This and other observations suggest that the coupled activation-inhibition changes that normally occur after head removal from the wild-type hydra do not occur in this strain. Mechanisms responsible for the wound reopening effect and the absence of activation-inhibition coupling in the mutant strain reg-16 are discussed.