title: Defining the cause of skewed X-chromosome inactivation in X-linked mental retardation by use of a mouse model.
abstract: Extreme skewing of X-chromosome inactivation (XCI) is rare in the normal female population but is observed frequently in carriers of some X-linked mutations. Recently, it has been shown that various forms of X-linked mental retardation (XLMR) have a strong association with skewed XCI in female carriers, but the mechanisms underlying this skewing are unknown. ATR-X syndrome, caused by mutations in a ubiquitously expressed, chromatin-associated protein, provides a clear example of XLMR in which phenotypically normal female carriers virtually all have highly skewed XCI biased against the X chromosome that harbors the mutant allele. Here, we have used a mouse model to understand the processes causing skewed XCI. In female mice heterozygous for a null Atrx allele, we found that XCI is balanced early in embryogenesis but becomes skewed over the course of development, because of selection favoring cells expressing the wild-type Atrx allele. Unexpectedly, selection does not appear to be the result of general cellular-viability defects in Atrx-deficient cells, since it is restricted to specific stages of development and is not ongoing throughout the life of the animal. Instead, there is evidence that selection results from independent tissue-specific effects. This illustrates an important mechanism by which skewed XCI may occur in carriers of XLMR and provides insight into the normal role of ATRX in regulating cell fate.
authors.affiliation: MRC Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, UK.
authors.forename: Mary R
authors.initials: MR
authors.lastname: Muers
authors.forename: Jacqueline A
authors.initials: JA
authors.lastname: Sharpe
authors.forename: David
authors.initials: D
authors.lastname: Garrick
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Sloane-Stanley
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Nolan
authors.forename: Terry
authors.initials: T
authors.lastname: Hacker
authors.forename: William G
authors.initials: WG
authors.lastname: Wood
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Higgs
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Gibbons
mesh_terms: D000483:Alleles; D000818:Animals; D003433:Crosses, Genetic; D004265:DNA Helicases / Q000235:genetics; D004195:Disease Models, Animal; D005260:Female; D005434:Flow Cytometry; D019084:Fluorescent Antibody Technique, Indirect; D006579:Heterozygote; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D038901:X-Linked Intellectual Disability / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics; D012641:Selection, Genetic; D014960:X Chromosome; D049951:X Chromosome Inactivation; D000075924:X-linked Nuclear Protein
chemical_list: D009687:Nuclear Proteins; D004265:DNA Helicases; C490462:Atrx protein, mouse; D000075924:X-linked Nuclear Protein