Changes in the cytoplasmic distribution of microtubule-associated protein 2 during the differentiation of cultured cerebellar granule cells.

The distribution of microtubule-associated protein 2 in cultured cerebellar granule cell neurons was followed by immunohistochemical staining with specific antibodies. During differentiation in vitro, the neurites of these cells pass through a series of developmental stages. At first the emergent processes contain only trace levels of microtubule-associated protein 2 which is most concentrated in and near the cell body. When the neurites are between two and five cell diameters long they exhibit both microtubule-associated protein 2 and tubulin, apparently evenly distributed, throughout their length. Subsequently microtubule-associated protein 2 is limited to an initial, usually varicose portion of the neurite whereas its long distal extension contains abundant tubulin but is apparently devoid of microtubule-associated protein 2. Thus microtubule-associated protein 2 and tubulin are not necessarily co-distributed with a single neuronal process. In both morphological appearance and in the different distributions of microtubule-associated protein 2 and tubulin they contain, these processes show a mixture of axonal and dendritic properties. Since these same cells do not develop their characteristic dendritic arborizations, our results suggest that when removed from the developing brain, cerebellar granule neurons achieve part but not all of their normal morphological and cytoskeletal differentiation.