Linking the Rb and polycomb pathways

Polycomb group (PcG) proteins associate to form complexes that repress Hox genes, thereby imposing the patterning of Hox expression required for devel opment. However, these proteins have a second Hox-independent role in regul ating cell proliferation. Our results suggest that association between Rb a nd PcG proteins forms a repressor complex that blocks entry of cells into m itosis. Also, we provide evidence that Rb colocalizes with nuclear PcG comp lexes and is important for association of PcG complexes with nuclear target s. The Rb-PcG complex may provide a means to link cell cycle arrest to diff erentiation events leading to embryonic pattern formation.