In the current study, we use a human cerebellar-derived medulloblastoma cell line to characterize three steps of the intercellular propagation of ATXN1 aggregates in Daoy cells: (1) the presence of cytoplasmic ATXN1 aggregates following nuclear aggregate formation, (2) extracellular propagation of ATXN1 aggregates via actin-based tunneling nanotubes, and (3) incorporation of aggregation-prone and aggregation-resistant ATXN1 proteins into seeded aggregate formations. This evidence concerns the gene ATXN1 and medulloblastoma.