Diacylglycerol-induced multihead formation in Hydra

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Abstract
Diacylglycerol (DAG) mediates transmembrane transduction for a wide variety of extracellular signals. Though pattern formation in multicellular organisms is, as a rule, based on intercellular signalling, reports on the participation of DAG in pattern-forming processes are lacking. Here evidence is presented for the involvement of DAG in pattern control in Hydra. Upon daily exposure to 1,2-dioctanoyl-sn-glycerol, wild-type polyps form ectopic heads along the gastric column in a periodic pattern and transform into phenocopies of a multiheaded mutant. The appearance of ectopic head structures is preceded by a (wave-like) increase in the positional value. Long before ectopic tentacles appear in the intact animal and, beginning with the first pretreatment, excised segments progressively fail to regenerate feet, form heads also at their lower end and eventually over the entire segment. DAG is the first physically defined substance found to induce, in hydra, an increase in the positional value and to evoke ectopic head formation.