Widespread distribution of the major polypeptide component of MAP 1 (microtubule-associated protein 1) in the nervous system.

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Abstract
A monoclonal antibody to microtubule-associated protein 1 (MAP 1), 1 of the 2 major high MW MAP found in microtubules isolated from brain tissue was prepared. MAP 1 can be resolved by SDS PAGE [sodium dodecyl sulfate polyacrylamide gel electrophoresis] into 3 electrophoretic bands, which were designated MAP 1A, MAP 1B and MAP 1C in order of increasing electrophoretic mobility. The antibody recognized exclusively MAP 1A, the most abundant and largest MAP 1 polypeptide. To determine the distribution of MAP 1A in nervous system tissue and cells, tissue sections from rat brain and spinal cord, as well as primary cultures of newborn rat brain were examined by immunofluorescence microscopy. Anti-MAP 1A stained white matter and gray matter regions, while a polyclonal anti-MAP 2 antibody previously prepared in this laboratory stained only gray matter. This confirmed earlier biochemical results, which indicated that MAP 1 is more uniformly distributed in brain tissue than MAP 2 (Vallee, R. B. 1982). To determine the identity of cells and cellular processes immunoreactive with anti-MAP 1A, a variety of brain and spinal cord regions were examined. Fibrous staining of white matter by anti-MAP 1A was generally observed. This was due in part to immunoreactivity of axons, as judged by examination of axonal fiber tracts in the cerebral cortex, and of large myelinated axons in the spinal cord and in spinal nerve roots. Cells with the morphology of oligodendrocytes were brightly labeled in white matter. Intense staining of Purkinje cell dendrites in the cerebellar cortex and of the apical dendrites of pyramidal cells in the cerebral cortex was observed. By double-labeling with antibodies to MAP 1A and MAP 2, the presence of both MAP in identical dendrites and neuronal perikarya was found. In primary brain cell cultures anti-MAP 2 stained predominantly cells of neuronal morphology. Anti-MAP 1A stained nearly all cells. Included among these were neurons, oligodendrocytes and astrocytes as determined by double-labeling with anti-MAP 1A in combination with antibody to MAP 2, myelin basic protein or glial fibrillary acidic protein, respectively. In contrast to MAP 2, which is specifically enriched in dendrites and perikarya of neurons, MAP 1A is evidently widely distributed in the nervous system.