DISTRIBUTION OF NCAM-180 AND POLYSIALIC ACID IN THE DEVELOPING TECTUMMESENCEPHALI OF THE FROG DISCOGLOSSUS-PICTUS AND THE SALAMANDER PLEURODELES-WALTL

The 180 kDa component of the neural cell adhesion molecule (NCAM-180), total NCAM (NCAM-total) and the polysialic acid modification of NCAM (PSA) show similar temporal and spatial regulation in the developing t ecta of Pleurodeles waltl (salamander) and Discoglossus pictus (frog). Whereas NCAM-total is found throughout the tectal tissue on neurons a nd glia, NCAM-180 is only found on non-proliferating neurons and in fi ber layers. PSA is expressed by a subset of NCAM-180-positive cells. W estern blots show that there is little polysialylated NCAM-140 in the developing amphibian tectum. Regions unstained for PSA and NCAM-180 co rrespond precisely to the growth zones of the tectum. NCAM- 1 80 and P SA are not present in tecta of early larvae. Staining intensity is str ongest at midlarval stages for both antigens. At metamorphosis, PSA is strongly downregulated, whereas NCAM-180 is downregulated in juvenile animals. Both antigens are still present in fiber layers of adult ani mals. In dissociated tissue culture of the frog tectum, NCAM-180 is no t present on astrocytes, but on neuronal cells. Expression is enhanced at cell contact sites, suggesting that NCAM-1 80 is involved in cell contact stabilization. This study shows that general features of tempo ral and spatial regulation of NCAM isoforms and PSA are highly conserv ed in frog and salamander tecta, despite large differences in the rate of cell migration and the degree of lamination in these homologous br ain regions.