Early oligodendrocyte progenitor cells in the human fetal telencephalon

Oligodendrocytes, the myelin-producing cells in the central nervous system, represent a large portion of the total number of cells in the human brain. Using cell-specific markers and antibodies to ventral homeodomain transcription factors, NKX2.1 and DLX2, we show here that a subpopulation of early oligodendrocyte progenitor cells (OPCs) in the human telencephalon may originate in the ganglionic eminence (GE). DLX2-labeled OPCs form a well-delineated stream of cells connecting the GE subventricular zone (SVZ) to the cortical intermediate zone through the anterior cortical SVZ. This population of cells is labeled by early OPCs markers, PDGFRalpha, Olig1, and NG2, and not with either neuronal, astrocyte, or late OPCs markers. Intriguingly, numerous CD68(+) microglia/macrophages, nestin(+) neural stem cells, and CD34(+) hematopoietic stem cells (HSCs) are also present in both the GE stream and the cortical SVZ. These cells could be colabeled with DLX2 as well as early OPCs markers. A separate subpopulation of early OPCs, present in the GE and cortical SVZ, did not express either DLX2 or CD68. These findings suggest that different subpopulations of early OPCs, characterized with different sets of transcription factors and cell-specific markers, are present in human forebrain. These subpopulations may have different origins; one may originate in the cortical SVZ, while others may come from the GE and/or outside the CNS as hematopoietic stem cells.