Regeneration potential in echinoderms: revisiting the regeneration concept

The potential for regenerating tissues, organs, and body parts, even the ability to reconstruct a complete animal from a body fragment, is expressed to a maximum extent in echinoderms which provide ideal deuterostome models for the study of regeneration. Regenerative processes following self-induced or traumatic damages are common in all classes of the phylum, even though specific capabilities differ between the taxa, depending on individual potential of morphogenetic and histogenetic plasticity at the whole body, tissue, and cellular levels. Regenerative phenomena, which are displayed by adults as well as by embryos and larvae independently of their developmental stage, always imply the crucial contribution of regeneration-competent cells (pluripotent/multipotent cells or dedifferentiated/transdifferentiated cells) employed in both repair and regenerative processes. In this review, we provide an overview of the current understanding of the phenomenon, giving an idea of the “state of the art” across the phylum in terms of experimental approaches and representative models, each model being unique for specificity and versatility and useful for unraveling the biological significance of regeneration and its relationships with developmental and asexual reproductive processes. We also rediscuss the crucial aspects of regeneration in terms of evolutionary implications, taking into account its possible primitive or derived origin, its reproductive or reconstructive role, and its adaptive or exaptive significance.