An ultrastructural and immunocytochemical study of astrocytic differentiation in vitro: changes in the composition and distribution of the cellular cytoskeleton.

Astroglia in cultures of dissociated neonatal rat optic nerves were studied by light microscopy, immunocytochemistry and electron microscopy to determine whether intermediate filaments play a role in defining the multipolar morphology of the mature astrocyte. Immature, polygonal astroblasts contained few glial filaments, in spite of exhibiting positive staining with antiserum against glial fibrillary acidic (GFA) protein. Microtubules were the most prominent cytoskeletal component at early stages of cytodifferentiation, but these were progressively reduced in number at later intervals and were gradually replaced by intermediate filaments. These observations suggest that microtubules are involved in the initial establishment of cytoplasmic asymmetry and process development. Subsequently, glial filaments may play a role in maintaining and stabilizing the overall geometry of the mature astrocyte.