Exploring echinoderm repair events after arm injury

Traumatic amputations are severe damages that can heavily impair animal life and survival. All animals are able to heal minor injuries but only few efficiently face the loss of whole body parts and completely regenerate them. Regeneration is prevented or limited if the initial repair phase is not ensured and highly effective. This is achieved only if different events properly occur, among which wound closure, inflammatory and immune responses, and extracellular matrix remodelling. Echinoderms are one of the best known examples of invertebrates displaying outstanding regenerative abilities. In this research the starfish Echinaster sepositus and the brittle star Amphiura filiformis were used as models to compare the main repair events after arm amputation using both microscopy and molecular tools. A comparison with the healing phenomena of scarcely regenerating models, such as mammals, is discussed as well. Our studies highlighted that the first emergency reactions, namely wound contraction and re-epithelialization, are similar in the two echinoderm species and faster and more effective than in mammals. The immunodetection of a TNF-α-like molecule suggested a possible conservation of this inflammatory pathway between echinoderm classes and within deuterostomes. Considering extracellular matrix remodelling, molecular analyses suggested that the identified collagen genes are not expressed in the new tissues till the beginning of the regenerative phase. This is in agreement with microscopy analyses that showed that collagen deposition is limited and delayed in both echinoderm species and in comparison to mammals. This difference may be relevant to understand why echinoderms subsequently regenerate so efficiently: indeed, abundant and quick scar formation and/or fibrosis in mammals have been suggested as a limiting factor for the regenerative process. Overall, echinoderms showed similar wound closure events, characterized by absence of fibrosis and delayed collagen deposition, and quicker and more efficient than those of mammals. Therefore, also considering their key phylogenetic position, they proved to be valid experimental systems to study the repair processes. Further molecular analyses must be performed to better understand the gene regulatory network and the molecule cross-talk underpinning echinoderms’ repair events and compare them with those of mammals to reveal fundamental similarities and differences between animals able and unable to regenerate.