title: X chromosome inactivation and active X upregulation in therian mammals: facts, questions, and hypotheses.
abstract: X chromosome inactivation is a mechanism that modulates the expression of X-linked genes in eutherian females (XX). Ohno proposed that to achieve a proper balance between X-linked and autosomal genes, those on the active X should also undergo a 2-fold upregulation. Although some support for Ohno's hypothesis has been provided through the years, recent genomic studies testing this hypothesis have brought contradictory results and fueled debate. Thus far, there are as many results in favor as against Ohno's hypothesis, depending on the nature of the datasets and the various assumptions and thresholds involved in the analyses. However, they have confirmed the importance of dosage balance between X-linked and autosomal genes involved in stoichiometric relationships. These facts as well as questions and hypotheses are discussed below.
authors.affiliation: Institut Jacques Monod, Paris, France Université Paris Diderot, Paris, France veitia.reiner@ijm.univ-paris-diderot.fr.
authors.forename: Reiner A
authors.initials: RA
authors.lastname: Veitia
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, CNRS/Université Montpellier II, Montpellier, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Veyrunes
authors.affiliation: Université Paris Diderot, Paris, France Matière et Systèmes Complexes, Paris, France.
authors.forename: Samuel
authors.initials: S
authors.lastname: Bottani
authors.affiliation: Division of Biological Sciences, University of Missouri, Columbia, MO, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Birchler
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D005260:Female; D018628:Gene Dosage; D005786:Gene Expression Regulation; D050172:Genes, X-Linked; D023281:Genomics; D006801:Humans; D008297:Male; D008322:Mammals / Q000235:genetics*; D012730:Sex Chromosomes; D015854:Up-Regulation; D049951:X Chromosome Inactivation
keywords: X chromosome upregulation; X inactivation; dosage balance; imprinting; monoallelic expression