A morphogenetically active compound has been isolated from tissue extract of Hydractinia echinata and identified to be N-methylpicolinic
acid (
homarine). When applied to whole animals,
homarine prevents metamorphosis from larval to adult stage and alters the pattern of adult structures. The concentration of
homarine in oocytes is about 25 mM. During embryogenesis, metamorphosis and early colony development the overall
homarine content does not change. Adult colonies contain a fourfold lower
homarine concentration than larvae. The
polyp's head contains twofold more
homarine than the gastric region and the stolons. A second, similarly active compound, N-methylnicotinic
acid (
trigonelline), has also been identified in Hydractinia tissue at concentrations about one-third that of
homarine. Incubation of larvae in 10 to 20 microM-
homarine or
trigonelline prevents head as well as stolon formation. If the compounds are applied in a pulse during metamorphosis, a large part of the available tissue forms stolons. Since microM concentrations of
homarine and
trigonelline are morphogenetically active, whereas mM concentrations are present in the tissue it appears that both substances are stored within the tissue.