Widespread cellular distribution of MAP-1A (microtubule-associated protein 1A) in the mitotic spindle and on interphase microtubules.

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Abstract
Microtubule-associated protein 1 (MAP 1) from brain was previously reported to comprise multiple protein species; the principal component, MAP 1A, can be detected in both neuronal and glial cells by immunofluorescence microscopy using a monoclonal antibody. The cellular and subcellular distribution of MAP 1A in commonly used cultured cell systems was determined here. Immunofluorescence microscopy and immunoblot analysis were used with anti-MAP 1A to examine 18 types of mammalian cell cultures. MAP 1A was detected in every culture system examined. Included among these were cells of mouse, rat, Chinese hamster, Syrian hanster, Potoroo (marsupial) and human origin derived from a broad variety of tissues and organs. Anti-MAP 1A consistently labeled mitotic spindles and stained cytoplasmic fibers during interphase in most of the cultures. These fibers were identified as microtubules by co-localization with tubulin in double-labeling experiments, by their disappearance in response to colchicine or vinblastine and by their reorganizaiton in response to taxol. The anti-MAP 1A stained microtubules in a punctate manner, raising the possibility that MAP 1A is located along microtubules at discrete foci that might represent sites of interaction between microtubules and other organelles. Verification that MAP 1A was, indeed, the reactive material in immunofluorescence microscopy was obtained from immunoblots. Anti-MAP 1A stained a band at the position of MAP 1A in all cultures examined. MAP 1A, a major MAP from brain, is widely distributed among cultured mammalian cells both within and outside of the nervous system.