MYCN and medulloblastoma: Using mice infected with RCAS-Shh RCAS-SHH in combination with RCAS-N-myc-T50A or RCAS-AKT-Myr Δ11–60 of Ntv-a wild-type p53 and Ntv-a p53-null background, Hambardzumyan et al. showed that similar to human medulloblastomas, nestin-expressing perivascular stem cells survive radiation, activate PI3K/Akt signaling, undergo PTEN/p53-dependent cell cycle arrest and shortly thereafter re-enter the cell cycle (127).