Genetic analysis of developmental mechanisms in hydra

Mutant hydra strains showing abnormal development can be isolated through sexual inbreeding of wild hydra. One such mutant strain, called reg-16, regenerates tentacles very poorly following amputation of the head and foot. Tentacle regeneration, however, is significantly enhanced by subdividing the regenerating fragment longitudinally. Lateral tissue implants that induce head formation in wild-type hydra either regress or induce foot formation in reg-16 polyps. These results suggest that regeneration deficiency in reg-16 is due to a defective polarity gradient. A chimaeric strain of hydra was produced by combining interstitial cells (and thus their differentiation products, nerve cells and nematocytes) of reg-16 hydra with epithelial cells of another strain which is capable of normal regeneration. The chimaeras regenerate normally, suggesting that the defect of reg-16 is not located in the interstitial or nerve cells.