Polycomb complex recruitment in pluripotent stem cells.

The recruitment of the silencing complex Polycomb group (PcG) to its target sites in mammalian cells has remained elusive. A prevalent model proposes that the PRC1 component is recruited through recognition of methylated H3K27 found at target sites occupied by the PRC2 component. However, mounting evidence suggests that PRC2-independent mechanisms of PRC1 recruitment exist. Three studies describe that the histone demethylase Kdm2b binds to unmethylated CpG islands and recruits a subset of PRC1 complexes to chromatin in pluripotent stem cells.