A developmentally regulated axonal glycoprotein (7-8D2 antigen) with a restricted distribution in mature rat brain

7-8D2 is a mouse monoclonal IgGl antibody which recognizes a neuronal cell surface antigen in rat brain. Immunohistochemical techniques reveal the antigen to be present most abundantly in the cerebellum of the adult brain, where it is expressed by the cell bodies and fibres of the granule neurons. Lower levels of staining were found in the neuropil of the hippocampus, in some fibres of the corpus callosum and in the most superficial layer of the cerebral cortex. Immunoelectron microscopy confirmed that the antigen was present on the surface of the parallel fibres in the cerebellum and showed that it was absent from glial, Purkinje or stellate cell membranes. The antigen had a more widespread distribution early in development, and the restricted adult distribution was achieved by the end of the second postnatal week. Immunoblotting of samples of adult rat brain shows that the antigen appears as a close doublet of bands at 211,000 mol. wt. This result was confirmed by immunoprecipitating the antigen from metabolically labelled glycoproteins prepared from cultured cerebellar interneurons. Immunoblotting and immunohistochemical experiments were in agreement that the cerebellum contained high levels of the antigen, and that lower but significant amounts could be found in other brain regions, notably the hippocampus and the cerebral cortex. The localization data and the changes in the distribution of the antigen may suggest some role for this molecule during early brain development.