Mechanisms of epigenetic inheritance: copying of polycomb repressed chromatin

A key problem in gene regulation is how transcription patterns can be stably maintained in dividing cells. The formation and propagation of chromatin structures is believed to underlie stable gene expression patterns, including those maintained by Polycomb Group proteins. Recent studies focused on how Polycomb Group proteins and the chromatin structures they create behave during DNA replication and have begun to shed light onto mechanisms by which chromatin structures may be propagated through S-phase. These studies suggest that both segregation of chromatin features to newly replicated chromatin and a feedback loop consisting of histone modification and recognition of this modification may contribute to inheritance. Results are discussed in light of other links between Polycomb proteins and DNA replication, and other systems in which maintenance of repression is believed to involve propagation of heritable chromatin structures.