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Faced with inequality: chicken do not have a general dosage compensation of sex-linked genes
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Evolutionary Biology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Evolutionary Biology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Physiology and Developmental Biology, Environmental Toxicology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmaceutical Biosciences.
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2007 (English)In: BMC Biology, ISSN 1741-7007, Vol. 5, no 1, 40- p.Article in journal (Refereed) Published
Abstract [en]

Background: The contrasting dose of sex chromosomes in males and females potentially introduces a large-scale imbalance in levels of gene expression between sexes, and between sex chromosomes and autosomes. In many organisms, dosage compensation has thus evolved to equalize sex-linked gene expression in males and females. In mammals this is achieved by X chromosome inactivation and in flies and worms by up- or down-regulation of X-linked expression, respectively. While otherwise widespread in systems with heteromorphic sex chromosomes, the case of dosage compensation in birds (males ZZ, females ZW) remains an unsolved enigma. Results: Here, we use a microarray approach to show that male chicken embryos generally express higher levels of Z-linked genes than female birds, both in soma and in gonads. The distribution of male-to-female fold-change values for Z chromosome genes is wide and has a mean of 1.4-1.6, which is consistent with absence of dosage compensation and sex-specific feedback regulation of gene expression at individual loci. Intriguingly, without global dosage compensation, the female chicken has significantly lower expression levels of Z-linked compared to autosomal genes, which is not the case in male birds. Conclusion: The pronounced sex difference in gene expression is likely to contribute to sexual dimorphism among birds, and potentially has implication to avian sex determination. Importantly, this report, together with a recent study of sex-biased expression in somatic tissue of chicken, demonstrates the first example of an organism with a lack of global dosage compensation, providing an unexpected case of a viable system with large-scale imbalance in gene expression between sexes.

Place, publisher, year, edition, pages
2007. Vol. 5, no 1, 40- p.
National Category
Pharmaceutical Sciences
URN: urn:nbn:se:uu:diva-96837DOI: 10.1186/1741-7007-5-40ISI: 000251423700001PubMedID: 17883843OAI: oai:DiVA.org:uu-96837DiVA: diva2:171545
Available from: 2008-03-14 Created: 2008-03-14 Last updated: 2011-03-01Bibliographically approved
In thesis
1. Genomic and Peptidomic Characterization of the Developing Avian Brain
Open this publication in new window or tab >>Genomic and Peptidomic Characterization of the Developing Avian Brain
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Chicken and Japanese quail are commonly used models in developmental and sex specific neuroendocrine research. There is relatively little known about the mechanisms behind their sex specific brain development, especially regarding the impact of the sex chromosomes (male: ZZ, female ZW) in relation to gonadal hormones. This thesis explores several aspects of these processes. Gene expression analysis with cDNA and Affymetrix arrays on brain tissue from both pre-gonadal embryos and embryos with differentiated gonads indicate a strong sex chromosomal presence in sexual dimorphic somatic tissue development in both chicken and Japanese quail. This sex chromosome pattern seems to remain in adult brain tissue. The data demonstrates that chicken males exhibit a significant level of Z-gene dosage compared to females in both somatic and germ line derived embryonic tissues. Several avian sex determination gene candidates (MHM non-coding RNA, DMRT1, HINTW, and HINTZ) were analyzed by real-time PCR. DMRT1 is dosage compensated in male brain tissue, in contrast to its reported gene dosage in male gonads. Early embryonic ethinylestradiol (EE2) exposure did not affect male or female neural gene expression patterns during later development. A peptidomics analysis on quail embryonic day 12 (ed12) and ed17 diencephalon by LC-MS identified over 60 endogenous peptides and analyzed the expression patterns for 38 of them with regard to age, sex and early EE2 exposure. There was a general upregulation between ed12 and ed17, but no clear sex effects were detected. Multivariate analysis indicates that EE2 exposed individuals differ from control individuals in a gender independent manner, and that Gonadotropin-inhibiting hormone related peptide 2 (GnIH-RP2) is a candidate for EE2 induced peptidomic alterations in male embryonic brain.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 67 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 317
Toxicology, Sex differentation, Sex determination, Sex chromosomes, Dosage Compensation, Genetic, Chickens, Coturnix, Gene Expression Profiling, Neuropeptides, Diencephalon, Toxikologi
National Category
Medical and Health Sciences
urn:nbn:se:uu:diva-8507 (URN)978-91-554-7117-0 (ISBN)
Public defence
2008-04-04, B42, BMC, Uppsala, 13:15
Available from: 2008-03-14 Created: 2008-03-14 Last updated: 2012-02-06Bibliographically approved

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