SHH and neoplasm: While several hedgehog-driven medulloblastoma mouse models have been generated and use Nestin, GFAP, or Math1 as driver lines for constitutive Shh pathway activity [27], [28], [29], [30], our Gdf7Cre/+;SmoM2 medulloblastoma mouse model demonstrates how remarkably few cells are sufficient for oncogenic transformation and tumor formation.