Cellular memory and dynamic regulation of polycomb group proteins.

Epigenetic components drive the inheritance of transcriptional programs. This cellular memory is crucial for the stable maintenance of cell fates throughout development. Polycomb group (PcG) proteins are central players in various epigenetic phenomena, such as the maintenance of Hox expression patterns from fruit flies to humans, X chromosome inactivation and imprinting in mammals. This cellular memory system involves changes at the chromatin level, through histone modifications and DNA methylation, as well as at the level of the nuclear architecture. Surprisingly, in addition to their role in the stable maintenance of repressive states, PcG factors are involved in more dynamic processes such as cellular proliferation and plasticity.