Apoptosis in pre-Bilaterians: Hydra as a model.

Hydra is a member of the ancient metazoan phylum Cnidaria and is an especially well investigated model organism for questions of the evolutionary origin of metazoan processes. Apoptosis in Hydra is important for the regulation of cellular homeostasis under different conditions of nutrient supply. The molecular mechanisms leading to apoptosis in Hydra are surprisingly extensive and comparable to those in mammals. Genome wide sequence analysis has revealed the presence of large caspase and Bcl-2 families, the apoptotic protease activating factor (APAF-1), inhibitors of apoptotic proteases (IAPs) and components of a putative death receptor pathway. Regulation of apoptosis in Hydra may involve BH-3 only proteins and survival pathways, possibly including insulin signalling.