At P16 the maturational stage and cell origin of oligodendrocyte lineage cells in septal corpus callosum were determined using fluorescent labeling. (A) The distribution of tamoxifen induced fluorescence expression in postnatal SVZ-derived cells (tdTomato+, red) and immunolabeled mature oligodendrocytes (Olig2+CC1+, green) across the corpus callosum (scale bar = 100 μm) (B) High resolution merged and split channel images, scale bars = 10 μm, demonstrating colabeled cells within the corpus callosum (DAPI, blue; Olig2, white; and tdTomato, red). Mature oligodendrocytes (OLs) are identified by Olig2 and CC1 (green) coexpression. Vertical white arrows point to a DAPI+ Olig2+ CC1+ cell that is tdTomato positive, indicative of a postnatally derived mature OL. C) Proliferating OPCs are identified by Olig2 and Ki67 (green) coexpression. Horizontal white arrows point to a DAPI+ Olig2+ Ki67+ cell that is tdTomato negative, indicative of an embryonically derived proliferating OPC. (D) Oligodendrocyte progenitor cells (OPCs) are identified by Olig2 and PDGFRα (green) coexpression. Split channel images demonstrate an embryonically derived tdTomato- (white horizontal arrow) and a postnatally derived tdTomato+ (white vertical arrow) OPCs (Olig2+ PDGFRα +).