Imprinted inactivation

The eed (embryonic ectoderm development) gene is a member of the mouse Polycomb group (Pc-G) and is required for early gastrulation. In the Advance Online issue of Nature Genetics, Jianbo Wang and colleagues from the University of North Carolina define a role for eed in X chromosome inactivation. They analysed trophoblast giant cells in eed-null embryonic deciduas and found developmental defects in eed-null females but not in male embryos. To investigate the role of paternal X inactivation, Wang et al. crossed the eed-mutant mice with mice carrying a paternally inherited X-linked green fluorescent protein (GFP) transgene. The presence of fluorescent extra-embryonic cells in eed-null females suggests that eed is essential for maintaining paternal X-inactivation. The authors propose a model in which interaction between the Eed protein and histone deacetylases maintains gene silencing on the imprinted X chromosome in mouse extra-embryonic tissues.