Arm-tip regeneration in the spiny starfish Marthasterias glacialis: an integrated approach

Starfish (Echinodermata, Asteroidea) possess striking regenerative capabilities being able to replace lost body structures after both autotomy and traumatic amputation. We selected the Mediterranean-Atlantic starfish Marthasterias glacialis (Linnaeus, 1758) as experimental model to study the arm-tip regeneration. The aims of this research are to describe in detail the complex cell and tissue patterning during M. glacialis regenerative process and to provide a complementary morphological perspective to previous and on-going proteomic studies [1]. Specimens of M. glacialis were collected in the west coast of Portugal (Estoril, Cascais) and subjected to traumatic arm-tip amputation. Regeneration tests were performed at different time-points: 48 hours, 13 days, 3, 6 and 10 weeks post amputation (p.a.). Regenerating samples were processed for both light and electron (TEM and SEM) microscopy analysis. As for other Asteroids, in M. glacialis the process can be divided in three main phases: a) repair phase (until 48h p.a.) during which wound closure and healing phenomena take place; b) early regenerative phase (13d–3w p.a.) where dedifferentiation, rearrangement and first signs of differentiation occur and c) advanced regenerative phase (up 3w p.a.) characterized by complete differentiation,morphogenesis and re-growth of the lost body structures with the formation of a miniaturized arm. Our results confirm that M. glacialis arm regeneration is mainly based on morphallactic mechanisms including 1) rearrangement and dedifferentiation of the stump tissues possibly used as source of cells (mainly from coelomic epithelium) for the subsequent regrowth of the new arm-tip, 2) lack of a well-defined undifferentiated blastema, although the presence of a widespread “blastemal connective tissue” is detectable, underlining the need to review classical epimorphosis/morphallaxis definitions. M. glacialis regenerative process can be well described by the “distalization-intercalation” regenerative model re-proposed for starfish by [2]: indeed, the first body structures reformed are the most distal ones and the new tissues subsequently differentiate by intercalation between these latter and the stump, following a proximal-distal gradient. Current proteomic studies on coelomic epithelium/cells will help to clarify the role of this tissue during regeneration. [1] Franco C.F. et al., 2011. Proteomics (2011), 11: pp 3587-3592. [2] Ben Khadra et al., 2015. WRR 23(4), pp 623-634.