Differential distribution of microtubule‐associated proteins MAP‐1 and MAP‐2 in neurons of rat brain and association of MAP‐1 with microtubules of neuroblastoma cells (clone N2A)

To study the individual location of the microtubule proteins MAP‐1 and MAP‐2 in neuronal tissues and cells, antisera to electrophoretically purified MAP‐1 and MAP‐2 components were raised in rabbits. When frozen sections through rat brain were examined by immunofluorescence microscopy the antibodies to MAP‐1 strongly stained a variety of nerve cells including dendrites and myelinated axons in the cerebrum and cerebellum. Antibodies to MAP‐2 showed similar staining patterns, except that myelinated axons were unstained. These results were confirmed by immunoelectron microscopy of frozen sections through cerebellum using the peroxidase technique. Thereby, the association of MAP‐1 with microtubules was also clearly demonstrated. When cultured mouse neuroblastoma N2A cells were examined by immunofluorescence microscopy the antiserum to MAP‐1 brightly stained filamentous structures resembling microtubules, whereas relatively weak and diffuse staining of the cytoplasm was observed with the antiserum to MAP‐2. In agreement with the immunolocalization, MAP‐1, but not MAP‐2, was found as a prominent component of microtubules proteins polymerized in vitro by taxol from soluble N2A cell extracts. Together these results indicate that neuronal microtubules are preferentially associated with distinct high mol. wt. polypeptides. Therefore, they support the concept that different complements of associated proteins determine distinct functions of microtubules.