To address this, we created a novel in vivo model of Shh-dependent medulloblastomas by directing constitutive expression of an activated form of Smoothened (SmoM2)24 in Otx2+ GCPs (Otx2CreERT2/+;R26SmoM2/SmoM2 line) and next investigated Otx2 function in tumour cell proliferation by simultaneous Otx2 ablation (Otx2CreERT2/flox;R26SmoM2/SmoM2 sKO line). The gene discussed is GLI3; the disease is neoplasm.