Polycomb group (PcG) proteins are chromatin-modifying complexes first identified in Drosophila, where they function in the epigenetic silencing of gene expression. In mammals, PcG proteins play critical roles in development, including regulation of homeotic genes and X chromosome inactivation. Dysregulation or overexpression of PcG proteins has been associated with increased severity and invasiveness in several cancers. The Drosophila Posterior Sex Combs (Psc) gene is a member of the PcG family and is essential for maintaining segmental identity during development. It is also the homolog of the murine Bmi1 oncogene, which is known to promote neural stem cell self-renewal.
