title: Reactivation of an inactive human X chromosome: evidence for X inactivation by DNA methylation.
abstract: A mouse-human somatic cell hybrid clone, deficient in hypoxanthine-guanine phosphoribosyltransferase (HPRT) and containing a structurally normal inactive human X chromosome, was isolated. The hybrid cells were treated with 5-azacytidine and tested for the reactivation and expression of human X-linked genes. The frequency of HPRT-positives clones after 5-azacytidine treatment was 1000-fold greater than that observed in untreated hybrid cells. Fourteen independent HPRT-positive clones were isolated and analyzed for the expression of human X markers. Isoelectric focusing showed that the HPRT expressed in these clones is human. One of the 14 clones expressed human glucose-6-phosphate dehydrogenase and another expressed human phosphoglycerate kinase. Since 5-azacytidine treatment results in hypomethylation of DNA, DNA methylation may be a mechanism of human X chromosome inactivation.
mesh_terms: D000818:Animals; D001374:Azacitidine / Q000494:pharmacology*; D001483:Base Sequence; D002454:Cell Differentiation; D004247:DNA / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics; D006801:Humans; D006822:Hybrid Cells / Q000502:physiology; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D008745:Methylation; D051379:Mice; D012730:Sex Chromosomes; D014960:X Chromosome
chemical_list: D004247:DNA; D005954:Glucosephosphate Dehydrogenase; D007041:Hypoxanthine Phosphoribosyltransferase; D001374:Azacitidine