HISTOCHEMICALLY DEFINED CELL STATES DURING TAIL FIN REGENERATION IN TELEOST FISHES

Teleost fin rays regenerate when they are cut, forming a distal prolif erating blastema that restores the entire structure in a few weeks. In the present study we have analysed the histochemical properties of th e cells and the extracellular matrix of regenerating fins in two teleo st species, Carassius auratus and Brachydanio rerio. Different cell ty pes and states have been defined. Four epidermal cell types, i.e. peri dermal, epidermal, basal epidermal and mucous cells, display different histochemical and lectin binding properties, depending on their distr ibution in the regenerative tissue. Blastema differentiates into two c ell types: scleroblasts and fibroblasts. The scleroblasts stem from bl astemal cells that have contacted the lateral palisade of actinotrichi a and begun to release lepidotrichial material beneath the subepiderma l basement membrane. The fibroblasts differentiate from blastemal cell s in the centro-proximal region of the blastema. Both cell types pass through transient states. Blastemal cells showed increased affinities for Concanavalin agglutinin, Ricinus communis agglutinin, toluidine bl ue and aldehyde-fuchsin, as they differentiated into scleroblasts and fibroblasts. Three different regions are histochemically distinguishab le in the precalcified lepidotrichial hemisegment, reflecting differen t degrees of maturation: mature matrix, central band and the periphera l (immature) region contacting scleroblasts. Maturation of lepidotrich ial matrix is characterized by the lost of affinity for lectins and st rong positivity for silver methenamine. A catalogue of position-depend ent histochemical affinities defining cell diversity in the regenerati ng fin of teleosts is proposed in order to correlate changes with the underlying regeneration mechanisms.