Polycomb mediated epigenetic silencing and replication timing at the INK4a/ARF locus during senescence.
BACKGROUND:The INK4/ARF locus encodes three tumor suppressor genes (p15(Ink4b), Arf and p16(Ink4a)) and is frequently inactivated in a large number of human cancers.Mechanisms regulating INK4/ARF expression are not fully characterized.PRINCIPAL FINDINGS:Here we show that in young proliferating embryonic fibroblasts (MEFs) the Polycomb Repressive Co