Institute for Genome Sciences and Policy, Department of Molecular Genetics and Microbiology, Duke University, Durham, NC 27710, USA.
Despite evidence implicating the Polycomb group protein, Eed (embryonic ectoderm development protein) in imprinted X inactivation, a similar role in random X inactivation in the embryo has remained an open question. Brockdorff and colleagues now report that Eed, along with its binding partner Enx1, transiently associates with the inactive X chromosome (Xi) and likely contributes to the epigenetic signature and long-term stability of the Xi heterochromatin.