Genetic analysis of developmental mechanisms in hydra. VIII. Head-activation and head-inhibition potentials of a slow-budding strain (L4).

Morphogenetic potentials involved in head formation were examined in a hydra strain (L4) which has a very low budding rate and a large polyp size, and the results were compared to those of the normal strain (105). Hydra tissue has two types of antagonistic morphogenetic potentials which are thought to play important roles in head structure formation: the head-activation potential and the head-inhibition potential. Lateral tissue transplantation (Webster & Wolpert, 1966) was used to compare the levels of the two potentials in L4 and the normal strain. It was found that the intact polyp of L4 has a nearly normal or slightly lower head-activation potential but a significantly higher head-inhibition potential than the normal strain. During the course of regeneration after head amputation, the levels of the two potentials in L4 changed in significantly different patterns from those in the normal strain. These abnormalities of the two potentials may be responsible for the developmental and morphological abnormalities in L4. The significance of these observations is discussed in light of the current hydra pattern formation models (Wolpert, Hornchurch & Clarke, 1974; Meinhardt & Gierer, 1974).