Glial cell lineages in the rat cerebral cortex

I have traced the fates of glial cell progenitors in the rat cerebral corte x marked with a recombinant retrovirus throughout most of the period of cor ticogenesis, from embryonic (E) day 14 to postnatal (P) day 14. Discrete cl usters of clonally related glia were examined in serially cut sections, and their phenotypes identified using reliable light and electron microscopic criteria. Analysis of a large number of clones marked with retrovirus at va rious stages of embryonic Life contained, with very few exceptions, either all astrocytes or all oligodendrocytes, This observation suggests that the ventricular zone contains separate progenitor cells for the two glial cell types. Oligodendrocyte clones were rarely seen in the cortices injected wit h retrovirus at the early stages of corticogenesis (E14-E16), suggesting th at there is a very small number of oligodendrocyte progenitors in the ventr icular zone at these early stages. Their frequency increased significantly at later embryonic ages. At these later stages, ventricular zone cells also give rise to progenitor cells that make up the subventricular zone in earl y postnatal life. Injections of retrovirus in this proliferative zone short ly after birth resulted in the generation of labeled astrocyte and oligoden drocyte clones in the cortical gray and white matter, with the astrocyte cl ones being in the majority. Injections at increasingly later stages resulte d in the presence, predominantly in the white matter of both hemispheres an d in the corpus callosum, of progressively more oligodendrocyte clones and fewer astrocyte clones. Injections at P14 generated only oligodendrocyte cl ones in the white matter of both hemispheres. A small number of clusters (< 10%) generated after subventricular zone injections contained both astrocyt es and oligodendrocytes, suggesting that single subventricular zone cells c an differentiate into both glial cell types. (C) 1999 Academic Press.