X inactivation analysis and DNA methylation studies of the ubiquitin activating enzyme E1 and PCTAIRE-1 genes in human and mouse
Department of Cell Biology
Medical Subject Headings
Animals; Chromosome Mapping; *Dosage Compensation, Genetic; Female; Gene Expression Regulation; Humans; Hybrid Cells; Ligases; Male; Methylation; Mice; Mice, Inbred BALB C; Mice, Inbred Strains; Protein-Serine-Threonine Kinases; Ubiquitin-Activating Enzymes; Ubiquitin-Protein Ligases; X Chromosome
Cell Biology | Life Sciences | Medicine and Health Sciences
Previously reported data on the X inactivation status of the ubiquitin activating enzyme E1 (UBE1) gene have been contradictory, and the issue has remained unsettled. Here we present three lines of evidence that UBE1 is expressed from the inactive X chromosome and therefore escapes X inactivation. First, by RNA in situ hybridization, UBE1 RNA is detected from both the active and inactive X chromosomes in human female fibroblasts. Second, UBE1 is expressed in a large panel of somatic cell hybrids retaining inactive human X chromosomes, including two independent hybrids that did not require UBE1 expression for survival. And third, sites at the 5' end of UBE1 are unmethylated on both active and inactive X chromosomes, consistent with the gene escaping inactivation. In order to address whether other genes that escape inactivation map to the same region of the X chromosome, we have also examined the expression of genes mapping adjacent to UBE1. The gene for PCTAIRE-1 (PCTK1) maps within 5 kb of UBE1 and similarly escapes X inactivation by the somatic cell hybrid assay, whereas six other genes that are within 1 Mb of UBE1 in Xp11.23 are silenced on the inactive X chromosome. Comparative mapping studies of the homologous loci in mouse establish that Ube1-x and Pctk1 are also within close physical proximity on the murine X chromosome, and expression studies of the Pctk1 gene determine that, similar to Ube1-x, it is subject to X inactivation in mouse. Methylation of CpG residues at restriction sites at the 5' end of both genes on the murine inactive X chromosome is consistent with both genes being subject to X inactivation in mouse, in contrast to their expression status in humans.
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Citation: Hum Mol Genet. 1996 Mar;5(3):391-401.