The role of Polycomb Group Proteins in Cell Cycle Regulation During Development

Polycomb group (PcG) and trithorax group (trxG) proteins are evolutionarilyconserved chromatin modifiers that have well known roles in the maintenance ofsilent and active expression states of homeotic genes. PcG proteins may also beinvolved in the control of cellular proliferation, as several PcG complexes have beenshown to act either as proto-oncogenes or as tumor suppressors in vertebrates. InDrosophila, PcG factors associate with specific DNA regions termed PcG responseelements (PREs), and a PRE was recently identified in the gene encoding Cyclin A.Still, it is not yet clear how PcG complexes could control cell cycle progression.Beyond acting as stable silencers of cell cycle genes during the differentiationprocess, PcG complexes might also be integrators and/or modulators of cell cyclecheckpoints in dividing cells. Here, we discuss this dual aspect of PcG involvement inepigenetic cell cycle control.