Fig. 2.

Cortical development shows disruption of upper layers and oligodendrocytes after APE1 loss. (A) The cortex (CTX) and corpus callosum (CC) are reduced in thickness, as is the hippocampal formation (HC) in the Ape1^Nes-cre brain. (B) DNA damage resulting from APE1 loss causes elevated γH2AX immunostaining and is more apparent in the upper-layer neurons (I–IV) of the cortex, while the lower-layer neurons (IV–VI) show little γH2AX immunoreactivity. White arrowheads indicate γH2AX cells that are apoptotic, while yellow arrows show the smaller γH2AX puncta indicative of DNA damage. (C) The illustration summarizes the change in the distribution of γH2AX/DNA damage as the cortex develops; darker shades of red indicate more γH2AX. (D) Apoptosis identified using TUNEL shows continual cellular attrition in the P7 and 6-wk-old Ape1^Nes-cre brain. (E, Upper) Specific cortical layer markers for upper-layer neurons (Satb2 and Brn2) are absent in the Ape1^Nes-cre cortex compared with WT controls. Tbr1, which primarily localizes to lower-layer neurons, is similar in the control and mutant tissue. (Lower) The graphs show quantitation of the loss of Satb2 and Brn2 in the Ape1^Nes-cre cortex compared with control cortex. ****P < 0.0001; ***P = 0.0002; n.s., not significant. (F) Myelin production indicated by CNPase immunostaining is markedly reduced in the corpus callosum (CC) of Ape1^Nes-cre mice. (G) Loss of oligodendrocytes is indicated by Sox10 immunostaining. The Ape1^Nes-cre cortex also has increased gliosis, as shown by GFAP immunostaining, suggesting a general perturbation of neural homeostasis.