CLUSTERING AND COLOCALIZATION OF IMMUNOGOLD DOUBLE-LABELED NEURAL CELL-ADHESION MOLECULE ISOFORMS IN CHICK FOREBRAIN

A quantitative immunoelectron microscopic study was carried out in the intermediate portion of hyperstriatum ventrale of chick forebrain (a region exhibiting learning-related morphological plasticity) in order to examine the fine distribution of the neural cell adhesion molecule (N-CAM). Antibodies against alpha 2,8 polysialic acid (PSA), characteristic for embryonic N-CAM, and those against the protein backbones of all N-CAM isoforms were sequentially labelled (post-embedding) with 5- and 15-nm gold particles, and binding to their epitopes was analyzed using the statistics of point processes. The results showed that: (1) PSA tends to form clusters (up to 200 nm in size), in contrast to the protein backbones of all N-CAM isoforms, and (2) the two tissue bound antibodies are colocalized spatially in clusters of sizes up to 100 nm. The data suggest that there is a spatial sub-cellular domain enriched in both PSA and protein isoforms of N-CAM.