EXPRESSION OF POLYSIALYLATED NEURAL CELL-ADHESION MOLECULE (PSA-N-CAM) IN DEVELOPING, ADULT AND REGENERATING CAUDAL SPINAL-CORD OF THE URODELE AMPHIBIANS

The patterns of expression of polysialylated (<<embryonic>>) form of N eural Cell Adhesion Molecule (PSA/E-N-CAM) and of all N-CAM isoforms w ere investigated by indirect immunofluorescence and immunoblotting dur ing the development of the Central Nervous System (CNS) and during the regeneration of the caudal Spinal Cord (SC) of the amphibian urodeles Pleurodeles waltl (Pw) and Notophthalmus viridescens (Nv). In this st udy, a monoclonal antibody to group B Meningococcus (anti-Men-B) which recognizes alpha-2,8-linked sialic units of PSA-N-CAM, and polyclonal anti-total N-CAM antibodies were used. Total-N-CAM immunoreactivities were consistently detected throughout the CNS of developing and adult newts. PSA-N-CAM expression predominated in <<embryonic>> developing CNS and was reduced to certain CNS areas in the adult urodeles. In the case of SC, the expression level of this isoform of N-CAM dramaticall y decreased to become low and nearly restricted to some ependymoglial cell surfaces. Interestingly, during newt tail regeneration, PSA-N-CAM was intensely reexpressed in regenerating SC, at the surface of epend ymoglial cell processes and in axonal compartments. Expression was max imal at 4 to 6 weeks following amputation, and then gradually returned to a normal adult low level in well differentiated SC. These findings strongly supported the view that the expression of PSA-N-CAM was asso ciated with the properties of plasticity shown by the SC ependymoglial tissue in newts, during tail regeneration. On the other hand, the hig h level of PSA-N-CAM expression in axonal compartments of regenerating as well as developing SC suggested that these isoforms of N-CAM could be implicated in axonal outgrowth within the <<tunnels>> defined by t he radial ependymoglial processes. This transient PSA-N-CAM expression could therefore be considered both as a negative modulator of cell-ce ll and cell-substrate interactions and as a permissive factor for neur on differentiation.