Developmental and post-injury cortical gliogenesis: a genetic fate-mapping study with Nestin-CreER mice.

The primary sources of cortical gliogenesis, either during development or after adult brain injury, remain uncertain. We previously generated Nestin-CreER mice to fate-map the progeny of radial glial cells (RG), a source of astrocytes and oligodendrocytes in the nervous system. Here, we show that Nestin-CreER mice label another population of glial progenitors, namely the perinatal subventricular zone (SVZ) glioblasts, if they are crossed with stop-floxed EGFP mice and receive tamoxifen in late embryogenesis (E16-E18). Quantification showed E18 tamoxifen-induction labeled more perinatal SVZ glioblasts than RG and transitional RG combined in the newborn brain (54% vs. 22%). Time-lapse microscopy showed SVZ-glioblasts underwent complex metamorphosis and often-reciprocal transformation into transitional RG. Surprisingly, the E10-dosed RG progenitors produced astrocytes, but no oligodendrocytes, whereas E18-induction fate-mapped both astrocytes and NG2+ oligodendrocyte precursors in the postnatal brain. These results suggest that cortical oligodendrocytes mostly derive from perinatal SVZ glioblast progenitors. Further, by combining genetic fate-mapping and BrdU-labeling, we showed that cortical astrocytes cease proliferation soon after birth (<P10) and only undergo nonproliferative gliosis (i.e., increased GFAP expression without cell-division) after stab-wound injury in adult brains. By contrast, 9.7% of cortical NG2+ progenitors remained mitotic at P29, and the ratio rose to 13.8% after stab-wound injury. Together, these results suggest NG2+ progenitors, rather than GFAP+ astrocytes, are the primary source of proliferative gliosis after adult brain injury.