Polycomb group (PcG) genes encode chromatin proteins that are involved in the maintenance of cellular memory throμgh epigenetic chromatin modifications. Bmi-1 has been identified among the PcG genes as a potent oncogene that plays an important role in the regulation of cell proliferation by suppressing the p16-dependant pathway. Bmi-1 may be use as a therapeutic target for studying stem cell proliferation and renewal.