A microtubule-associated protein (MAP1) which is expressed at elevated levels during development of the rat cerebellum.

Monoclonal antibody (MAb) G10 labels a single high mol. wt. (HMW) band on Western blots of microtubule preparations from 2 day old rat brain. The G10 antigen is thermolabile and co-migrates with microtubule-associated protein (MAP)1 from young rat brain on low percentage (5%) polyacrylamide-SDS gels. The G10 antigen decreases by about five times from birth to adulthood in the rat cerebellum. The same single band is labelled on Western blots of homogenates of whole neonatal rat brain but no labelling is found using neonatal or adult kidney, lung or liver. We have therefore identified a brain-specific MAP1, designated MAP1(x). Immunofluorescence microscopy using MAb G10 on parasagittal sections of rat cerebella shows labelling of the newly formed molecular layer in 6 day old rats. Only a narrow band close to the pial surface is labelled in 18 day old animals, which disappears in the adult. Labelling of the cerebellar white matter found in young rats also disappears. Neurones but not flat cells in cerebellar cultures label with MAb G10. All staining patterns are consistent with an axonal distribution of the antigen. MAP1(x) may be part of a developmentally regulated microtubule structure.