PRC1 and cancer: We confirmed by qRT-PCR that MUC1 and WDR5 increase expression of (i) SALL4, an ESC effector of pluripotency and self-renewal53, (ii) HIF1A, which is overexpressed in human cancers in association with hypoxia54, (iii) BMI1, a component of PRC1 and effector of H2A ubiquitylation that binds directly to MUC1-C55, and (iv) LGR5, which is necessary for maintenance of breast CSCs56 (Fig. 6c, d).