Tail fin regeneration in teleosts: cell-extracellular matrix interaction in blastemal differentiation.

The fins of teleosts are appendices capable of regenerating by an epimorphic process that completely restores in a few days the original shape and size. After a partial amputation, the process that follows consists of: wound healing, blastema formation and cell differentiation to form a particular cell population responsible for the building of the different tissue elements. The present work deals with the histochemical and ultrastructural characterisation of the extracellular matrix (ECM) components in different blastemal regions. In the subepidermal space of the tip of a regenerating ray, two zones can be identified: the blastema proper (BP) that occupies the more apical region and extends proximally along the centre of the regenerating ray, and the actinotrichial blastemic region (ABR), located laterally to the former, about some micrometres beneath the tip and tightly related with the palisade of the actinotrichia. Hyaluronate is the more prominent glycosaminoglycan (GAG) in BP whereas sulphated GAGs and collagen are scarce in distal portions but they can be identified proximally. In the ABR a network composed mainly of sulphated GAGs and in part of collagen is developed. This network connects the actinotrichia of each palisade and extends around them. The significance of the ECM components in the morphogenetic processes of the regenerating rays is discussed. In addition a model for the synthesis of lepidotrichia by lepidotrichium-forming cells, differentiated from blastemal cells, is given.