TP53 and medulloblastoma: Notably, these changes in the histone machinery in SI-CSC medulloblastomas were reproducible in vitro in long-term LDE225-treated Ptch;p53 and FSmoM2;hGFAP-cre primary medulloblastoma tumorspheres (Fig. 4G), indicating a generalizable epigenetic mechanism that occurs both in vivo and in vitro.