PTEN restrains SHH medulloblastma growth through cell autonomous and nonautonomous mechanisms.

A third of patients with the pediatric cerebellar tumor Medulloblastoma (MB) have mutations that activate Sonic hedgehog (SHH) signaling (SHH-MB subgroup). The contribution of secondary mutations to tumor severity, however is not clear. mutations are enriched in the SHH-1 subtype that has the lowest survival rate. Widespread heterozygous loss of in two SHH-MB mouse models increases penetrance and excellerates onset of differentiated tumors. We delineated cellular and transcriptional changes that accelerate tumor growth and cause differentiation using a sporadic SHH-MB mouse model expressing oncogenic SmoM2 in rare cerebellar granule cell precursors (GCPs) and scRNA-seq analysis. Homozygous but not heterozygous sporadic loss of resulted in rapid acceleration of tumor growth and end stage disease by 40 days, compared to ~25% survival in control mice at 100 days. Heterozygous mutations therefore should negatively impact disease outcome primarily with germline mutations. Loss of in normal or SmoM2-expressing GCPs increased proliferation and enhanced progenitor state initially but by 12 days mutant tumors were highly differentiated due to increased survival of non-proliferating GCPs. Furthermore, macrophage infiltration and cytotoxicity were reduced in differentiated regions of tumors lacking , indicating cell nonautonomous changes also contribute to accelerated tumor growth.