TENASCIN EXPRESSION IN DEVELOPING, ADULT AND REGENERATING CAUDAL SPINAL-CORD IN THE URODELE AMPHIBIANS

Tenascin (Tn) protein and transcripts were analyzed in developing, adu lt and regenerating caudal spinal cord (SC) of Pleurodeles waltl. A po lyclonal antibody (PAb) against Xenopus Tn and a newt Tn cDNA probe we re used. In Western blots, anti-Tn PAb recognized Tn polypeptides of 2 00-220 kDa in tail regenerate extracts, but also the homolog of Tn/Cyt otactin/J1 in brain and SC of adult newt. Immunofluorescence studies s howed some reactivity around ependymoglial cells and strong labeling i n the nervous tracts, in the developing as well as in the regenerating SC or adult SC. Immunogold electron microscopy revealed the presence of Tn throughout the ependymoglial cells, particularly near and along the plasma membrane of radial processes surrounding axons, especially growth cones. Tn could be more precisely found within rough endoplasmi c reticulum and Golgi structures, or again in the surrounding extracel lular space. This suggested that Tn was at least produced by radial gl ial profiles forming axonal compartments in which axons grew. Using th e DNA probe for Tn, expression of Tn mRNA was also examined by Norther n blot and RNAase protection analyses and by in site hybridization, re spectively. The levels of transcripts, barely detectable in adult tail , increased in regenerates from 3 days through 4-8 weeks post-amputati on. In situ Tn mRNA were mainly localized in the mesenchyme, especiall y at the epithelial-mesenchymal interface, and in the developing carti lage, at the early regeneration stages, whereas high amounts of transc ripts were seen not only at these stages, but also later, in the regen erating SC. Our main results supported the view that, in the caudal SC of newts, Tn, synthesized by radial ependymoglial cells, was similarl y expressed during regeneration as well as larval development, and exh ibited a sustained high accumulation level in the adult SC. On the bas is of the multifunctional properties of Tn, the putative roles played by Tn as a substrate for neuronal pathfinding and boundary shaping wer e discussed.