Methylation of the Hprt gene on the inactive X occurs after chromosome inactivation

Cell. 1987 Jan 16;48(1):39-46. doi: 10.1016/0092-8674(87)90353-9.


DNA sequences have previously been identified in the first intron of the mouse Hprt gene that are methylated on the inactive but not the active X chromosome. The temporal relationship between methylation of these sequences and X-inactivation was studied in teratocarcinoma cells and postimplantation mouse embryos: the sequences are unmethylated prior to X-inactivation and do not become methylated on the inactive X in most fetal cells until several days postinactivation. Such inactive X-specific methylation occurs in a significantly smaller proportion of the cells in the extra-embryonic tissues, yolk sac mesoderm and endoderm, than in the fetus. These data suggest that the inactive X-specific methylation of sequences such as those in the first intron of the Hprt gene does not play any role in the primary events of X-inactivation, but may function as part of a secondary, tissue-specific mechanism for maintaining the inactive state.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Dosage Compensation, Genetic*
  • Female
  • Gene Expression Regulation
  • Gestational Age
  • Hypoxanthine Phosphoribosyltransferase / genetics*
  • Introns
  • Methylation
  • Mice
  • Teratoma / genetics
  • X Chromosome / physiology*
  • Yolk Sac / physiology


  • Hypoxanthine Phosphoribosyltransferase