Localization of an epitope of a microtubule-associated protein 1x in outgrowing axons of the developing rat central nervous system.

We have shown that monoclonal antibody, G10, labels developing rat cerebellum in a manner consistent with the presence of microtubule-associated protein 1x in growing axons. In this paper we show that all growing axons investigated in post-natal and pre-natal developing rat brain contain microtubule-associated protein 1x and that neither dendrites, cell bodies nor glia are labelled by G10. The distribution of the G10 epitope as shown by immuno-electron microscopy is consistent with its localization to axonal microtubules. On Western blots there is only a small decrease in microtubule-associated protein 1x from first-natal day 7 to adulthood, in contrast to the dramatic decrease in immunofluorescence during axonal maturation. The G10 epitope is therefore probably masked in adult brain. The spatial and chronological coincidence of the G10 epitope with axonal elongation offers the possibility of using this monoclonal antibody to probe the function of the cytoskeleton during neuronal growth.