Shh-subtype medulloblastoma (SHH-MB) is thought to arise from GC lineage precursors99,100 and relies on Atoh1 for tumor initiation.30,86 Similar to the development of GC lineage, SHH-MB also follows a hierarchical pattern.9,101,102 Heterogeneous cell subpopulations within the tumor tissue recapitulate different developmental stages of GC lineage cells.101 Our discovery that Sin3A’s stage-specific functions in GC lineage progression suggests a more intricate role for Sin3A in SHH-MB. The gene discussed is ATOH1; the disease is medulloblastoma.