RPS6KB1 and osteosarcoma: As S6K inactivation promoted only a partial osteogenic differentiation of SSEA-4+ TICs (Supplementary Fig. 4j), we wanted to investigate the downstream mechanisms of mTORC1 in the regulation of dedifferentiation versus terminal maturation of partially differentiated SSEA-4− osteosarcoma cells, as this marks a critical point for retention or elimination of tumorigenicity.