Paternal X chromosome expression in extraembryonic membranes of XO mice.

The paternally derived allelic form of the X chromosome linked enzyme phosphoglycerate kinase (PGK-1) is expressed in both the fetus and extraembryonic membranes of 9.5 day post coitum XO (XpO) mouse conceptuses. Previous studies on trophectoderm and primitive endoderm derived extraembryonic membranes in XX conceptuses suggest expression of only the maternally derived X chromosome (Xm). Our results suggest that the observed lack of expression of Xp in the trophectoderm and primitive endoderm derivatives of XX embryos is not an intrinsic property of the Xp chromosome.