Distribution of the head-activating substance in hydra and its localization in membranous particles in nerve cells

Abstract

The low-molecular-weight substance activating head and bud formation in hydra is shown to occur in the animal as a gradient decreasing from the hypostomal to the basal region. The concentration of head-activating substance increases during head regeneration and during bud initiation. Most of the low-molecular-weight head-activating substance is present in the animal in a structure-bound form. More than 90% was sedimentable; 70% was recovered in a highly purified fraction consisting of membranous particles of ∽1200 Å diameter. This implies that in the animal only a minor portion of the total activating activity is freely diffusible, i.e. present in the low-molecular-weight form. The head-activating substance is mainly produced by and/or stored in nerve cells or a subgroup of the nerve cells. Nerve cells were enriched tenfold in a fraction containing most of the head-activating substance in a more than 10 times higher specific activity than in the animal. In addition, it is shown that only the nerve cells are positively correlated with the distribution of head-activating activity both with regard to localization within the animal as to time sequence of appearance during head regeneration and bud formation.