Evidence for a foot-inhibiting substance in hydra.

Crude extracts of hydra contain a substance or substances which specifically inhibit foot formation in regenerating hydra. This foot inhibitor(s) is probably of low molecular weight, and it is present in the animal in an inactive, structure-bound form as a gradient from foot to head. The foot region contains 60% of this inhibitor in a 7-8 fold higher concentration than the other regions. The foot inhibitor was purified chemically from the head activator (Schaller, 1973) and the 'head' inhibitor (Berking, 1974). It is suggested that the substance under investigation is a new morphogen, responsible for foot inhibition in hydra.