Patterns and Cellular Mechanisms of Arm Regeneration in Adult Starfish Echinaster sepositus

Adult echinoderms from each of the five classes exhibit natural, rapid regeneration of entire lost parts following predation or other traumatic events. The asteroids represent one of the echinoderms’ classes used traditionally as experimental models to study limbs regeneration, though very little is known on the cellular mechanisms and patterning. In this study we have chosen “Echinaster sepositus”, the widespread sea star in the Mediterranean as a model with the aim of making a descriptive scenario of the regrowth of missing arm-tip. The regeneration process can be subdivided into three phases: a) a repair phase, which is characterized by wound healing (re-epithelialization) and “edema” formation; b) an early regenerative phase, during which beginning of first differentiation events occurs (skeletogenesis) and c) an advanced regenerative phase characterized by differentiation, morphogenesis and growth of the bud. Our results confirm that regeneration in asteroids is a morphallactic process which usually consists in a rearrangement of the existing tissues through dedifferentiation, differentiation and/or migration of cells in order to regenerate the lost body structures, without a strong contribution of proliferative events. A true blastema is not formed during arm-tip regeneration in this sea star. Therefore, an epimorphollactic process could be involved during regeneration of removed ossicles. This supports the hypothesis of the combination of both processes during regeneration. To confirm such conclusions it’s worthy to use molecular and biochemical approaches.