GDF7 and medulloblastoma: Consistent with the fact that constitutively active SmoM2 was expressed in Gdf7-lineage cells and the tumor cells are marked by YFP, we detected a high level of Shh signaling, as evidenced by robust expression of pathway target genes Gli1 and Ptch1 in Gdf7Cre/+;SmoM2 medulloblastomas (Figure 2B and 2B′).