Neuropeptides and their functions in Hydra.

In order to identify novel peptide signaling molecules involved in the regulation of developmental and physiological processes in the freshwater cnidarian, Hydra magnipapillata, we initiated a systematic peptide screening project, the Hydra Peptide Project. In the project, twelve neuropeptides were identified so far. The LWamide family is composed of seven members, which share a GLWamide motif at their C-termini. All the peptides have an ability to induce metamorphosis of Hydractinia serrata planula larvae into polyps. In Hydra, LWamides induce detachment of the bud from a parental polyp. A neuropeptide, Hym-355, enhances neuronal differentiation by inducing the multipotent interstitial stem cells to enter the neuron differentiation pathway. A myoactive neutopeptide, Hym-176, specifically and reversibly induces contraction of the ectodermal muscle of the body column, in particularly in the peduncle region of epithelial Hydra that totally lack nerve cells. Two members of a novel neuropeptide family (FRamides) were contained in the same precursor. However, they have opposite myoactive functions in epithelial hydra. From these results, it seems fair to say reasonable to conclude that the so-called 'primitive' nervous system of Hydra is in reality more complex than generally believed.