Regenerating echinoderms : a promise to understand stem cell potential

The potential for regenerating tissues, organs and body parts, even the ability to reconstruct virtually a complete animal from a body fragment, is expressed to a maximum extent in echinoderms which provide fantastic and tractable models for the study of regeneration. Regenerative processes are common in all classes of the phylum, even though specific capabilities differ remarkably between the classes, depending on individual potential of morphogenetic and histogenetic plasticity at tissue and most of all at cellular levels. These phenomena, particularly in adults, imply the existence of stem cells which can be present in the circulating fluids or in the tissues in the form of resident cells, ready to be recruited in the repair and regenerative processes that follow traumatic or self-induced damage. In spite of the impressive effectiveness of their regenerative processes, only a few model systems for the study of regeneration have been developed in echinoderms, each model being unique for its specificity and versatility, and useful for unravelling peculiar aspects of the phenomenon. In addition, larvae of all classes display a unique capacity for rapid regeneration regardless of their developmental stage, showing an unexpected plasticity in terms of processes and mechanisms closely related to events of asexual reproduction and cloning. On the basis of their regenerative potential echinoderms can provide a broad range of valuable new deuterostome models for the study of regeneration genetics, with potential applications in vertebrate regeneration. Since the complexity of the echinoderm genome, as exemplified by the sea urchin genome project, indicates that echinoderms share at least 70% of their proteins with mankind, we shall consider how this provides an important tool kit to aid our understanding of the phenomenon as well as support the development of realistic methods to pursue tissue and organ regeneration in humans.