The development pattern of a 31,000 mol. wt phosphatidyl inositol-anchored membrane glycoprotein was followed during development in mouse and rat cerebellum using monoclonal antibody 194-653. The epitope was developmentally regulated and particularly abundant in post mitotic precursors of granule cells, newly formed parallel fibres and unmyelinated axons of the white matter between the 5th and the 15th postnatal days. It decreased considerably thereafter. In the adult, a significant although relatively low staining was observed only in white matter. Observation at the ultrastructural level showed that most of the 31,000 mol. wt glycoprotein was very concentrated on neuronal plasma membranes. A little immunoreactivity was also found intracellularly at the perinuclear membrane of neuroblasts of the external germinal layer. The antigen was present in the coated pits and intracellularly in coated vesicles. Immunochemical studies indicated that 31,000 mol. wt antigen was very likely to be a previously identified transient concanavalin A-binding glycoprotein insoluble in neutral detergents (Reeber et al., 1981; Brain Res. 229, 53-65). It appeared to be one of the glycoprotein ligands for two endogenous mannosyl-lectins isolated from rat cerebellum (Zanetta et al., 1985, Devl. Brain Res. 17, 233-243, Zanetta et al., 1987, J. Neurochem. 49, 1250-1257). The affinity of the 31,000 mol. wt glycoprotein for the two endogenous lectins, together with its developmental pattern and localization indicate that it could be an important molecule for contact guidance during migration of neurons and for myelination and could take part in other ontogenetic steps.
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