In embryo analysis of H3K27 trimethylation suggests a two-step process involving PRC2 interacting sequences and high GC content

ABSTRACT Polycomb group (PcG) proteins are essential for the repression of key developmental regulators during development. In Drosophila, the polycomb repressive complexes (PRC) associate with defined DNA sequences termed polycomb response elements (PREs). In mammals, however, the mechanisms underlying polycomb recruitment at targeted loci are poorly understood. We have used an in vivo approach to try and map DNA sequences of importance for the proper recruitment of polycomb proteins within the genetically well-characterized HoxD genomic locus. Here, we report that relatively small polycomb interacting sequences appear necessary and sufficient to confer polycomb recognition and targeting to ectopic loci. These elements synergize, when clustered together, to form a fully functional repressive domain. In addition, a high GC content, while not sufficient to recruit PRC2, may help its local spreading. We discuss the importance of PRC2 recruitment over Hox gene clusters, in embryonic stem cells, for their subsequent coordinated transcriptional activation during development. ChIP-chip using K27 antibodies