Bmi1 plays a central role in senescence and aging, regulating the expression of relevant genes involved in aging and cancer.41, 42, 43 Overexpression of Bmi1 results in repression of the tumor suppressor p16INK4a, which has emerged as a major regulator of aging and age-associated pathologies.44 We show that in CPCs, Bmi1, and miR-300 oppositely regulate expression of p16Ink4a and p19ARF. Expression of p16Ink4a is decreased in CPCs upon Bmi1 and miR-300 upregulation (Figure 2c); in contrast, p19ARF levels are upregulated. This evidence concerns the gene BMI1 and cancer.