PPP1R15A and medulloblastoma: Bromodeoxyuridine (BrdU) labeling (Figure 4A–4C, 4M) and proliferating cell nuclear antigen (PCNA) IHC (data not shown) showed that GADD34 mutation, either heterozygous or homozygous, did not significantly affect the number of proliferating cells in medulloblastoma in Ptch1+/− mice.