Increased number of OPCs in Pen-2 cKO mice. A, IHC on Olig2. Images for the cortex and the thalamus at P14 are shown. B, IHC on Pdgfrα. Boxed areas in Ba and Bb were enlarged as Be and Bf, respectively. Scale bars: Ba-Bd, 50 µm; Be, Bf, 10 µm. C, Relative number of Olig2⁺ and Pdgfrα⁺ cells in 1 mm² area in the cortex and the thalamus. There were significant differences on relative numbers for Olig2⁺ and Pdgfrα⁺ cells between control and Pen-2 cKO mice at P14 (n = 4 mice per group). **p < 0.01. ***p < 0.005. D, Western blotting for Olig2, Pdgfrα, and Sox10. There were significant differences on relative levels for Olig2, Pdgfrα, and Sox10 between control and Pen-2 cKO mice at P14 (Control: n = 3; Pen-2 cKO: n = 4). **p < 0.01. ***p < 0.005. GAPDH served as the loading control. E, Representative images for double immunostaining for Pdgfrα and BrdU. BrdU was injected into mice at P7. Images were taken from the cortex. Scale bar, 50 µm. F, Percentage of Pdgfrα⁺/BrdU⁺ cells to Pdgfrα⁺ cells in the cortex. There was a highly significant difference between control and Pen-2 cKO mice (Control: 100 ± 2.9%, n = 4 mice; Pen-2 cKO: 168.4 ± 4.4%, n = 4 mice). ****p < 0.001.