ATOH1 and medulloblastoma: We examined tumours of both genotypes (Ptc1lox/lox;Math1-Cre and Ptc1lox/lox;RBP-Jlox/lox;Math1-Cre) in more detail and observed that the tumour mass is made up of small round granular cells interspersed with stroma in both cases (Figure 4A,B), similar to human medulloblastoma and as previously published [38].