Nematocyte differentiation in hydra.

Nematocyte differentiation from interstitial stem cells in hydra occurs in a highly position-dependent manner along the body axis. The results of the studies summarized here have shown that the morphogenetic factors involved in head formation are probably not responsible for this. Whether the morphogenetic factors involved in foot formation are responsible has not been determined. A new factor, presumably unrelated to any of the known morphogens, has been identified which specifically inhibits the developing nematoblasts to differentiate into stenoteles. This factor is present in a gradient along the body column, and appears to be responsible, at least in part, for producing position-dependent nematocyte differentiation. Nematoblasts which normally differentiate into one nematocyte type can be altered to differentiate into another by means of regeneration or treatment with stenotele inhibitor. This alteration occurs near the S/G2 boundary in the terminal cell cycle in the nematocyte differentiation pathway. It appears that either the nematoblasts are not committed to any specific nematocyte pathway until this critical time, or the nematoblasts committed to differentiate into a specific type can transdifferentiate into another type at this step.