RBPJ and medulloblastoma: In conclusion, even though Notch signalling is lost in the majority of cells in Ptc1lox/lox;RBP-Jlox/lox;Math1-Cre tumours, as confirmed by loss of Hes5 mRNA, RBP-J deletion does not appear to influence the characteristics of medulloblastoma initiated by Ptc1 deletion in GNPs.