In vitro analysis of the oligodendrocyte lineage in mice during demyelination and remyelination

Proliferation of mature and immature oligodendrocytes in vivo has been described in several electron microscopic and autoradiographic studies of experimental demyelination in adult CNS (Herndon et al., 1977; Ludwin, 1979; Aranella and Herndon, 1984; Raine et al., 1988) . In our in vivo studies of remyelination following coronavirus-induced demyelination in mice, we have used in situ hybridization and immunolabeling techniques to analyze the expression of myelin genes and the presence of cell-type-specific antigens in oligodendrocytes and their precursors (Jordan et al., 1989; Godfraind et al., 1989) . We found that myelin basic protein mRNA isoforms containing exon-2, which are normally abundant only during development, are reexpressed at dramatically increased levels during remyelination (Jordan et al., 1990) . This recapitulation of molecular events characteristic of development suggests that newly generated oligodendrocytes are responsible for remyelination in this disease. Studies using triple-label immunocytochemistry combined with autoradiography have identified O-2A progenitor cells in 1 ~m frozen sections of the spinal cord of these infected mice (Godfraind et al., 1989) . O-2A progenitors and O4-positive astrocytes proliferated early in the course of the disease and some Figure 12 . An O-2A adult progenitor cultured from demyelinated tissue (4 wpi) and processed as described in Fig. 10 is recognized by its reactivity with the 04 antibody (A; rhodamine optics) and in the absence of staining with GC (B; fluorescein optics) or GFAP (C; coumarin optics) antibodies. The cluster of silver grains over the nucleus (D, arrow) indicates that this cell incorporated [3H]thymidine during the 20-h in vitro pulse. (E) Phase contrast showing the cell processes. Note that numerous microglial cells are also present in this culture. Bar, 50 #m. cells generated during the demyelination stage later developed into oligodendrocytes (Godfraind et al., 1989) .