Early specification of oligodendrocytes in the chick embryonic brain

Oligodendrocytes are the myelin-forming cells in the central nervous system of vertebrates. In the rodent embryo, these cells have been shown to emerg e from restricted territories of the neuroepithelium. However, a comprehens ive view of the development of oligodendroglial populations from their vent ricular sources remains to be established. As a first step toward this aim, we have examined in vivo the spatiotemporal emergence of oligodendrocytes in the chick embryonic brain. We have detailed the patterns of expression o f three early markers of the oligodendroglial lineage: the plp/dm-20 and PD GFR alpha transcripts and the O4-reactive antigen. During embryonic develop ment, these molecules showed a similar segmental pattern of expression. How ever, plp/dm-20(+) cells were already observed, in the ventricular layer, a t E2.5, i.e., 2 days before the appearance of O4(+) and PDGFR alpha(+) cell s, suggesting that oligodendrocyte precursors arise nearly simultaneously w ith neurons. In the chick embryonic brain, the onset of expression of plp/d m-20 appears therefore to be the earliest event indicative of oligodendrogl ial specification and we propose, based on the expression of plp/dm-20 tran script, a ventricular map of the foci at which oligodendrocytes originate. In addition, we document the precocious segregation, from E5, of plp/dm-20( +) and PDGFR alpha(+) oligodendroglial cells in the subventricular and mant le layers of the brain. (C) 1999 Academic Press.