Widespread occurrence of polypeptides related to neurotubule‐associated proteins (MAP‐1 and MAP‐2) in non‐neuronal cells and tissues

The occurrence and cellular localization of polypeptides related to hog brain microtubule‐associated proteins 1 and 2 (MAP‐1 and MAP‐2) in non‐neuronal cell lines of various species and types, and in several tissues from rat was studied. When insoluble cell fractions were prepared by incubation of isotonic cell extracts with 20 microM taxol, polypeptides co‐migrating with MAP‐1 and MAP‐2 upon gel electrophoresis were observed in virtually all cases examined. Immunoblotting of preparations from 3T6, CHO, HeLa and N2A cells, as well as pituitary, heart, testis and liver revealed immuno‐reactivity with antibodies to neuronal MAP‐1 for polypeptides co‐migrating with MAP‐1 in all cases, except for HeLa cells and liver. With similar preparations, antibodies raised to neuronal MAP‐2 were barely reactive with bands of the MAP‐2 size except for N2A cells and pituitary gland. In all cases of non‐neuronal cells and tissues, major cross‐reactive bands, however, were of mol. wt. lower than that of MAP‐2, indicating, most likely, proteolytic breakdown of MAP‐2 during cell fractionation. As shown by double immunofluorescence microscopy of various cultured cell lines using affinity‐purified antibodies to MAPs, and monoclonal antibodies to tubulin, MAP‐1‐as well as MAP‐2‐related antigens were generally, but not exclusively, associated with typical microtubule structures of the cytoplasm, spindle, midbody and primary cilia. Antigens related to both MAPs were also localized in frozen sections of rat trachea, testis, pituitary, kidney and cardiac and skeletal muscle.