These invertebrates can live almost forever and their fertility rates does not decline. The incredible regenerative abilities found in the group of cnidarians seems to be brought to perfection in the Hydra. The three stem cell types (ectodermal, endodermal and interstitial epithelial cells) have the capability to proliferate endlessly and differentiate to many cell types, so that the Hydra can replace its old cells and fully rejuvenate its full body. There are great possibilities to discover age-disabling processes, since that the Hydra shares more than 6000 genes with the human genome.

One of the promising genes found in the Hydra is FoxO, which is apparently key genes that regulates the proliferation of stem cells and their stress response. In higher organisms it belongs to a core unit which modulates a plethora of metabolic pathways (apoptosis, DNA damage repair, oxidative stress, cell differentiation etc.). Perhaps trying to activate our stem cells to rejuvenate old cells is a way to slow down the decline of our organism.


Bridge D, Theo fi les AG, Holler RL, Marcinkevicius E, Steele RE, Martinez DE. 2010. FoxO and stress responses in the Cnidarian Hydra vulgaris. PLoS ONE. 5:e11686.

Martinez  DE and Bridge D. 2012, Hydra, the everlasting embryo, confronts aging.

Salih DAM, Brunet A. 2008. FoxO transcription factors in the maintenance of cellular homeostasis during aging. Current Opinion in Cell Biology. 20:126 – 136.

Tomczyk S, Fischer K, Austad S, Galliot B. 2015. Hydra, a powerful model for aging studies. Invertebrate Reproduction and Development. 59:11-16