Ultrastructural features of cultured oligodendrocytes expressing stage-specific cell-surface antigens

This study was designed to correlate cytological features that had previously been established for oligodendrocytes at different developmental stages in vivo and cytological criteria in vitro with the expression of stage-specific cell-surface antigens of cultured oligodendrocytes. Cells obtained from the corpus callosum of 10-day-old C57BL/6J mice were maintained in monolayer cultures and stained with monoclonal antibodies 01 through 012 by indirect immunofluorescence or immunoperoxidase methods. 0 antigen-positive cells were classified according to two criteria: (a) cell shape (type I-III); and (b) cytoplasmic features at the ultrastructural level (class 1-3). Approximately 95% of all 0 antigen-positive cells could be identified as oligodendrocytes by established cytological criteria, thus supporting previous evidence of their glial character from electrophysiological and cell type-specific marker studies. After 12 days in vitro approximately 90% of all morphologically identified oligodendrocytes expressed antigens 03, 04, 05 or 06, which are the first to appear during development in vivo, whereas only 30-40% expressed antigens 011 or 012 which are the last to appear during development in vivo. 01 through 010 antigen-positive oligodendrocytes belong to 3 morphologically distinct cell types: (1) with small (approximately 10 micron in diameter) round cell bodies and few slender processes; (2) with 'hairy eyeball' morphology with a network of processes; and (3) with large, sometimes bipolar cell bodies (up to 30 micron in diameter) surrounded by high amounts of membranous material devoid of cytoplasm. By cytoplasmic criteria at least 90% of all 0 antigen-positive cells fit the description by Mori and Leblond of 'light' to 'medium' oligodendrocytes in vivo, although a clear-cut correlation with expression of early or late appearing 0 antigens was not observed. Typically 'dark' oligodendrocytes were rarely seen in our cultures. 011 and 012 antigen-positive cells are restricted to the group of large oligodendrocytes with high amounts of membranous material, often organized in more or less compact structures (type III). In contrast to the more uniform localization of antigens 01 through 010 over the whole cell surface, antigens 011 and 012 are less strongly detectable on cell bodies than on processes and membranous whirls.