Abstract

Research performed on vertebrate and invertebrate model systems have demonstrated the potential of adult stem cells that represent a hope for regenerative medicine. In parallel since 2006, we know that differentiated cells can be manipulated as such as they reactivate their stem cell potential. Beside the pressure of patients for regenerative medicine, there is a need to better understand the mechanisms that regulate cellular as well as tissue plasticity. Hydra is a small freshwater cnidarian polyp that exhibits a highly dynamic maintenance of its body shape and fitness, a strong regenerative potential upon injury, and a low senescence. As such it provides a unique model system to investigate the relationships between tissue plasticity and regenerative potential. Hydra properties rely on three distinct stem cell populations that cannot replace each other, ectodermal and endodermal epithelial stem cells, both unipotent, and interstitial stem cells, multipotent. Surprisingly the suppression of the multipotent interstitial cells is compatible not only with survival of the animal but also with the reactivation of their adult developmental programs, i.e. regeneration and asexual reproduction ,i.e. budding. I will present experimental strategies that investigate the specific properties of these three stem cell populations, their cycling activity, their resistance to cell death, their response to injury and the molecular pathways linked to these behaviors.