PTCH1 and neoplasm: To characterize the molecular pathomechanism underlying the tumor-promoting effect of Nos2 deficiency in Ptch1+/− mice, we performed comprehensive expression and DNA copy number profiling of MB tumors (Ptch1+/− Nos2+/+ versus Ptch1+/− Nos2−/−) as well as expression profiling of normal cerebellar tissue samples from different developmental stages and various genotypes (Ptch1+/− Nos2+/+, Ptch1+/− Nos2−/−, Ptch1+/+ Nos2−/− and wild-type mice).