SIGNALS AND SIGNAL-TRANSDUCTION SYSTEMS IN THE CONTROL OF DEVELOPMENTIN HYDRA AND HYDRACTINIA

Pattern control in Hydra has traditionally been assigned to the determ ining influence of morphogens and neuropeptides. However, at present, arachidonic acid and its derivative 12-S-HETE are the only identified, potential signal molecules known to promote head and bud formation. M ore potent factors might exist but are not yet identified. Nonetheless , it is possible to evoke the development of an almost unlimited numbe r of supernumerary head structures and to induce ectopic foot formatio n by interference with the PI-PKC signal transducing system. Such an i nterference can also rescue the regeneration-deficient mutant reg-16. Regarding signals in the development of Hydractinia, metamorphosis is induced by an external key stimulus, i.e. a lipid derived from environ mental bacteria. The reception of this stimulus involves PKC-mediated responses. Upon its reception, a neuropeptide is released as an intern al, synchronising signal. Members of the novel LWamide family of pepti des appear to represent this internal signal. In postmetamorphic devel opment, a glycoprotein SIF serves as an inducer of stolen formation.