Spatiotemporal development of oligodendrocytes in the embryonic brain

In the central nervous system (CNS), oligodendrocytes have long been consid ered to be the last cell type to be generated during development. In rodent s, the progenitor cells that give rise to oligodendrocytes have been report ed to originate in the subventricular zone. Here, we review recent data dem onstrating the existence of oligodendrocyte precursor cells in the ventricu lar layer of the neural tube that emerge prior to the progenitor stage. Oli godendrocyte precursors arise in restricted foci that are distributed along the rostrocaudal axis of the neural tube, for the most part ventrally. The generation of oligodendrocyte precursor cells occurs either simultaneously with, or follows closely upon the emergence of the first neurons. Experime nts with quail-chick chimeras provide evidence that oligodendrocyte progeni tors derived from ventricular precursors migrate either tangentially or rad ially to colonize extensive or segmentally retricted territories of the bra in, The choice depends on their site of origin. Finally, we discuss the pos sibility that oligodendrocytes could be a mosaic population that originates from at least two types of precursor cells. (C) 2000 Wiley-Liss, Inc.