Imprinted by Eed

Imprinted genes are subject to epigenetic regulation and undergo parent-of-origin-specific allelic silencing. Many imprinted genes have been shown to contain a differentially methylated region (DMR). In an Advanced Online Publication in Nature Genetics Jesse Mager and colleagues at the University of North Carolina at Chapel Hill report a role for the Polycomb-group protein Eed (for 'embryonic ectoderm development'), a histone methyltransferase, in epigenetic regulation at imprinted loci (Nature Genetics, 10 March 2003, DOI:10.1038/ng1125). Eed^-/- knockout embryos showed upregulation of a subset of paternally-repressed imprinted genes. Loss of imprinting may account in part for the lethality of Eed-knockout embryos. Eed mutation did not affect parent-of-origin methylation, but it did cause changes in the methylation of certain CpG dinucleotides in the DMR of imprinted genes. These data provide the first link between mammalian Polycomb-group proteins and genome imprinting.