title: Spontaneous reactivation of the inactive X chromosome in mouse embryonal carcinoma cells.
abstract: The mouse embryonal carcinoma cell line MC12 carries two X chromosomes, one of which replicates late in S phase and shares properties with the normal inactive X chromosome and, therefore, is considered to be inactivated. Since the hypoxanthine phosphoribosyl transferase (HPRT) gene on the active X chromosome is mutated (HPRT(NDASH;)), MC12 cells lack HPRT activity. After subjecting MC12 cells to selection in HAT medium, however, a number of HAT-resistant clones (HAT(R)) appeared. The high frequency of HAT resistance (3.18 x 10(-4)) suggested reactivation of HPRT(PLUS;) on the inactive X chromosome rather than reversion of HPRT(NDASH;). Consistent with this view, cytological analyses showed that the reactivation occurred over the length of the inactive X chromosome in 11 of 20 HAT(R) clones isolated. The remaining nine clones retained a normal heterochromatic inactive X chromosome. The spontaneous reactivation rate of the HPRT(PLUS;) on the inactive X chromosome was relatively high (1.34 x 10(-6)) and comparable to that observed for XIST-deleted somatic cells (Csankovszki et al., 2001), suggesting that the inactivated state is poorly maintained in MC12 cells.
authors.affiliation: Laboratory of Gene Function and Regulation, Center for Advanced Science and Technology, and Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, Japan. ikuya@rmg.hokudai.ac.jp
authors.forename: I
authors.initials: I
authors.lastname: Yoshida
mesh_terms: D000630:Aminopterin / Q000494:pharmacology; D000818:Animals; D002455:Cell Division / Q000235:genetics; D003470:Culture Media / Q000737:chemistry / Q000494:pharmacology; D004303:Dosage Compensation, Genetic; D004351:Drug Resistance / Q000235:genetics; D054278:Embryonal Carcinoma Stem Cells; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006570:Heterochromatin / Q000235:genetics; D019271:Hypoxanthine / Q000494:pharmacology; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics; D013936:Thymidine / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014960:X Chromosome / Q000235:genetics*
chemical_list: D003470:Culture Media; D006570:Heterochromatin; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; C077885:XIST non-coding RNA; D019271:Hypoxanthine; D007041:Hypoxanthine Phosphoribosyltransferase; D000630:Aminopterin; D013936:Thymidine