title: Variable escape from X-chromosome inactivation: identifying factors that tip the scales towards expression.
abstract: In humans over 15% of X-linked genes have been shown to 'escape' from X-chromosome inactivation (XCI): they continue to be expressed to some extent from the inactive X chromosome. Mono-allelic expression is anticipated within a cell for genes subject to XCI, but random XCI usually results in expression of both alleles in a cell population. Using a study of allelic expression from cultured lymphoblasts and fibroblasts, many of which showed substantial skewing of XCI, we recently reported that the expression of genes lies on a contiunuum between those that are subject to inactivation, and those that escape. We now review allelic expression studies from mouse, and discuss the variability in escape seen in both humans and mice in genic expression levels, between X chromosomes and between tissues. We also discuss current knowledge of the heterochromatic features, DNA elements and three-dimensional topology of the inactive X that contribute to the balance of expression from the otherwise inactive X chromosome.
authors.affiliation: Department of Medical Genetics, Molecular Epigenetics Group, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Samantha B
authors.initials: SB
authors.lastname: Peeters
authors.forename: Allison M
authors.initials: AM
authors.lastname: Cotton
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Brown
mesh_terms: D000818:Animals; D041321:Chromosomes, Human, X / Q000235:genetics / Q000648:ultrastructure; D019175:DNA Methylation; D019143:Evolution, Molecular; D015870:Gene Expression; D050172:Genes, X-Linked; D006801:Humans; D049951:X Chromosome Inactivation
keywords: RNA-seq; XIST; allelic imbalance; boundary elements; dosage compensation; epigenetic marks; waystations