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Activity map of the tammar X chromosome shows that marsupial X inactivation is incomplete and escape is stochastic

Al Nadaf, Shafagh; Waters, Paul D.; Koina, Edda; Deakin, Janine E.; Jordan, Kristen S.; Graves, Jennifer A.

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BACKGROUND: X chromosome inactivation is a spectacular example of epigenetic silencing. In order to deduce how this complex system evolved, we examined X inactivation in a model marsupial, the tammar wallaby (Macropus eugenii). In marsupials, X inactivation is known to be paternal, incomplete and tissue-specific, and occurs in the absence of an XIST orthologue. RESULTS: We examined expression of X-borne genes...[Show more]

dc.contributor.authorAl Nadaf, Shafagh
dc.contributor.authorWaters, Paul D.
dc.contributor.authorKoina, Edda
dc.contributor.authorDeakin, Janine E.
dc.contributor.authorJordan, Kristen S.
dc.contributor.authorGraves, Jennifer A.
dc.date.accessioned2016-01-03T23:46:27Z
dc.date.available2016-01-03T23:46:27Z
dc.identifier.citationGenome Biology. 2010 Dec 23;11(12):R122
dc.identifier.issn1465-6906
dc.identifier.urihttp://dx.doi.org/10.1186/gb-2010-11-12-r122
dc.identifier.urihttp://hdl.handle.net/1885/95201
dc.description.abstractBACKGROUND: X chromosome inactivation is a spectacular example of epigenetic silencing. In order to deduce how this complex system evolved, we examined X inactivation in a model marsupial, the tammar wallaby (Macropus eugenii). In marsupials, X inactivation is known to be paternal, incomplete and tissue-specific, and occurs in the absence of an XIST orthologue. RESULTS: We examined expression of X-borne genes using quantitative PCR, revealing a range of dosage compensation for different loci. To assess the frequency of 1X- or 2X-active fibroblasts, we investigated expression of 32 X-borne genes at the cellular level using RNA-FISH. In female fibroblasts, two-color RNA-FISH showed that genes were coordinately expressed from the same X (active X) in nuclei in which both loci were inactivated. However, loci on the other X escape inactivation independently, with each locus showing a characteristic frequency of 1X-active and 2X-active nuclei, equivalent to stochastic escape. We constructed an activity map of the tammar wallaby inactive X chromosome, which identified no relationship between gene location and extent of inactivation, nor any correlation with the presence or absence of a Y-borne paralog. CONCLUSIONS: In the tammar wallaby, one X (presumed to be maternal) is expressed in all cells, but genes on the other (paternal) X escape inactivation independently and at characteristic frequencies. The paternal and incomplete X chromosome inactivation in marsupials, with stochastic escape, appears to be quite distinct from the X chromosome inactivation process in eutherians. We find no evidence for a polar spread of inactivation from an X inactivation center.
dc.description.sponsorshipThis project was funded by grants to JAMG and PDW from the Australian Research Council.
dc.publisherBioMed Central
dc.rights© 2010 Nadaf et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
dc.sourceGenome Biology
dc.subjectKeywords: animal cell; article; cell nucleus; chromosome analysis; chromosome map; controlled study; female; fibroblast; gene expression; gene location; gene locus; Macropus eugenii; male; marsupial; nonhuman; orthology; paralogy; stochastic model; X chromosome ina
dc.titleActivity map of the tammar X chromosome shows that marsupial X inactivation is incomplete and escape is stochastic
dc.typeJournal article
dc.language.rfc3066en
dc.rights.holderNadaf et al..
local.identifier.citationvolume11
dc.date.issued2010-12-23
local.identifier.absfor060408 - Genomics
local.identifier.ariespublicationu9511635xPUB711
local.publisher.urlhttp://www.biomedcentral.com/
local.type.statusPublished Version
local.contributor.affiliationAl Nadaf, S., Research School of Biology, The Australian National University
local.contributor.affiliationWaters, P. D., ARC Centre of Excellence for Kangaroo Genomics, Research School of Biology, The Australian National University
local.contributor.affiliationKoina, E., Research School of Biology, The Australian National University
local.contributor.affiliationDeakin, J. E., Research School of Biology, The Australian National University
local.contributor.affiliationJordan, K. S., Research School of Biology, The Australian National University
local.contributor.affiliationGraves, J. A., Research School of Biology, The Australian National University
local.bibliographicCitation.issue12
local.bibliographicCitation.startpageR122
local.identifier.doi10.1186/gb-2010-11-12-r122
local.identifier.absseo970106 - Expanding Knowledge in the Biological Sciences
dc.date.updated2016-02-24T12:07:59Z
local.identifier.scopusID2-s2.0-78650389025
local.identifier.thomsonID000287379000004
CollectionsANU Research Publications

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