PTCH1 and medulloblastoma: In the Ptch1 heterozygous mouse model of medulloblastoma, studies of proliferation kinetics and genetic lineage tracing have shown that slow-cycling Sox2-positive stem-like cells at the apex of a hierarchy give rise to highly proliferative intermediates (marked by Dcx and Ki67 expression) that differentiate into NeuN-positive neurons, which then undergo rapid apoptosis (Vanner et al., 2014).