Re‐growth, morphogenesis, and differentiation during starfish arm regeneration

Abstract

The red starfish Echinaster sepositus is an excellent model for studying arm regeneration processes following traumatic amputation. The initial repair phase was described in a previous paper in terms of the early cicatrisation phenomena, and tissue and cell involvement. In this work we attempt to provide a further comprehensive description of the later regenerative stages in this species. Here we present the results of a detailed microscopic and submicroscopic investigation of the long regenerative phase, which can be subdivided into two sub-phases: early and advanced regenerative phases. The early regenerative phase (1-6 weeks p.a.) is characterized by tissue rearrangement, morphogenetic processes and initial differentiation events (mainly neurogenesis and skeletogenesis). The advanced regenerative phase (after 6 weeks p.a.) is characterized by further differentiation processes (early myogenesis), and obvious morphogenesis and re-growth of the regenerate. As in other starfish, the regenerative process in E. sepositus is relatively slow in comparison with that of crinoids and many ophiuroids, which is usually interpreted as resulting mainly from sizerelated aspects and of the more conspicuous involvement of morphallactic processes. Light and electron microscopy analyses suggest that some of the amputated structures, such as muscles, are not able to replace their missing parts by directly regrowing them from the remaining tissues, whereas others tissues, such as the skeleton and the radial nerve cord, appear to undergo direct re-growth. The overall process is in agreement with the distalizationintercalation model proposed by Agata and co-workers (1). Further experiments are needed to confirm this hypothesis.

Post‐metamorphic ontogeny of Zoroaster fulgens Thomson, 1873 (Asteroidea, Forcipulatacea)

“…Asteroid ossicles commence growth as intracellular spicules that later differentiate into ossicles through the addition of extracellular calcite deposits (Ben Khadra et al. ; Czarkwiani et al. ).…”

“…), as well as during arm regeneration (Ben Khadra et al. , ; Czarkwiani et al. ) or spine regeneration (Dubois & Jangoux, ).…”

“…Recent work on the regeneration process in echinoderms, especially the regeneration of the asteroids and ophiuroids arms, has shown that regeneration follows a ‘distalization‐intercalation’ model (Ben Khadra et al. ,b, ; Czarkwiani et al. ).…”

“…The regeneration can be divided into three main phases: (i) the repair phase during the first hours/days post‐amputation; (ii) the early regenerative phase; and (iii) the advanced regenerative phase (Candia Carnevali & Bonasoro, ; Ben Khadra et al. ,b, ). It is during the early regenerative phase that ‘distalization‐intercalation’ occurs, i.e.…”

Expression of stem cell factors in the adult sea cucumber digestive tube

“…Sea cucumbers, and echinoderms in general, are known for the plasticity of their adult tissues (Franco et al, 2013; Mashanov et al, 2014a; Ben Khadra et al, 2015). One manifestation of this plasticity is the capacity to autotomize (eviscerate) and then quickly regrow the digestive tube and associated visceral structures.…”