Oligodendroglial progenitor cells but not oligodendroglia divide during normal development of the rat cerebellum

To identify the stage in the life cycle of oligodendroglia at which they are mitotic during normal in vivo development [3H]thymidine autoradiography has been combined with immunocytochemistry on frozen sections of rat cerebellum. A panel of antibodies have been used that recognize antigens expressed by oligodendroglia at different stages of differentiation from progenitor to mature cell. It has been demonstrated that of the cells of the oligodendroglial lineage only the progenitors, identified by their expression of the ganglioside GD3, were seen to incorporate [3H]thymidine at all the developmental stages tested. Only few dividing GD3-positive cells were observed in the subventricular zones of the fourth-ventricle. The greatest number of dividing GD3-positive progenitors in the rat cerebellum was observed in the folia at postnatal day 7. Silver grains were never observed over cells that could be distinguished as oligodendroglia by their expression of galactocerebroside, 2'3'-cyclic nucleotide 3'-phosphohydrolase, or myelin basic protein. Mitotic astroglia were observed at all stages and could be clearly distinguished by their expression of glial fibrillary acidic protein and glutamine synthetase. When animals were injected with [3H]thymidine at postnatal day 7 and killed at 1-day intervals radiolabel was first observed in galactocerebroside-positive and 2'3'-cyclic nucleotide 3'-phosphohydrolase-positive oligodendroglia at day 9 and in myelin basic protein-positive cells at day 10-11, 3 days after the last cell division. Thus, we have demonstrated for the first time using in situ immunocytochemical techniques, a mitotic glial progenitor cell that is known to give rise to oligodendroglia both in vivo and in vitro.