Conditional inactivation of key repair factors of either of these two pathways, such as BRCA2 (HR), XRCC4, or Lig4 (cNHEJ) in nestin-expressing or Emx1-expressing neural progenitor cells leads to medulloblastomas (MBs) or high-grade gliomas (HGGs) in mouse models with a p53-deficient background8,9 (Peter McKinnon, personal communication). Here, TP53 is linked to medulloblastoma.