Methylation of the Hprt gene on the inactive X occurs after chromosome inactivation.
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.
D000818:Animals; D004303:Dosage Compensation, Genetic; D005260:Female; D005786:Gene Expression Regulation; D005865:Gestational Age; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D007438:Introns; D008745:Methylation; D051379:Mice; D013724:Teratoma / Q000235:genetics; D014960:X Chromosome / Q000502:physiology*; D015017:Yolk Sac / Q000502:physiology
D007041:Hypoxanthine Phosphoribosyltransferase