Extensive proliferation of oligodendrocyte precursors in the parenchyma ofthe embryonic chick central nervous system

The proliferation of oligodendrocyte lineage cells in the chick embryo cent ral nervous system (CNS) was examined by double-immunolabeling with a linea ge marker monoclonal antibody (mAb) 04 or mAb 01 and 5-bromo-3'-deoxyuridin e (BrdU). In all regions examined, the first 04-positive (04+) cells appear ed in restricted regions of the ventricular zone (VZ), regarded as a site o f oligodendrocyte origin. Within the 04+ focus, less than 20% of the 04+ ce lls incorporated BrdU. In contrast, 04+ cells in the parenchyma were mitoti cally active; for example, 40-50% of early 04+ cells were labeled with BrdU . Some of these were unipolar in shape, indicative of migratory precursor c ells. The frequency of 04+/BrdU+ cell appearance decreased to less than 20% with further development. 01+ oligodendrocytes were largely mitotically in active, with only approximately 5% of 01+ cells incorporating BrdU. These r esults clearly demonstrated that the VZ generates relatively few precursor cells and that these oligodendrocyte precursors actively generate their coh ort in the parenchyma of the CNS. (C) 2001Academic Press.