AP site appearances in mutUNG1-expressing mice. (a) Coronal cryosections of the hippocampus and cerebellum probed with an aldehyde-reactive probe and stained with DAPI demonstrate a high level of AP sites, but only in the hippocampus of induced mutUNG1 mice. Scale bar, 100 μm. (b) AP sites are only seen in parts of the hippocampus containing mitochondria, not nuclei, as demonstrated here in a mutUNG1 mouse induced for 3 months. Scale bar, 25 μm.