Gene duplication and fragmentation in the zebra finch major histocompatibility complex

Balakrishnan, Christopher N. and Ekblom, Robert and Völker, Martin and Westerdahl, Helena and Godinez, Ricardo and Kotkiewicz, Holly and Burt, David W. and Graves, Tina A. and Griffin, Darren K. and Warren, Wesley C. and Edwards, Scott V. (2010) Gene duplication and fragmentation in the zebra finch major histocompatibility complex. BMC Biology, 8 (1). p. 29. ISSN 1741-7007. (doi:https://doi.org/10.1186/1741-7007-8-29) (Full text available)

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http://dx.doi.org/10.1186/1741-7007-8-29

Abstract

BACKGROUND: Due to its high polymorphism and importance for disease resistance, the major histocompatibility complex (MHC) has been an important focus of many vertebrate genome projects. Avian MHC organization is of particular interest because the chicken Gallus gallus, the avian species with the best characterized MHC, possesses a highly streamlined minimal essential MHC, which is linked to resistance against specific pathogens. It remains unclear the extent to which this organization describes the situation in other birds and whether it represents a derived or ancestral condition. The sequencing of the zebra finch Taeniopygia guttata genome, in combination with targeted bacterial artificial chromosome (BAC) sequencing, has allowed us to characterize an MHC from a highly divergent and diverse avian lineage, the passerines. RESULTS: The zebra finch MHC exhibits a complex structure and history involving gene duplication and fragmentation. The zebra finch MHC includes multiple Class I and Class II genes, some of which appear to be pseudogenes, and spans a much more extensive genomic region than the chicken MHC, as evidenced by the presence of MHC genes on each of seven BACs spanning 739 kb. Cytogenetic (FISH) evidence and the genome assembly itself place core MHC genes on as many as four chromosomes with TAP and Class I genes mapping to different chromosomes. MHC Class II regions are further characterized by high endogenous retroviral content. Lastly, we find strong evidence of selection acting on sites within passerine MHC Class I and Class II genes. CONCLUSION: The zebra finch MHC differs markedly from that of the chicken, the only other bird species with a complete genome sequence. The apparent lack of synteny between TAP and the expressed MHC Class I locus is in fact reminiscent of a pattern seen in some mammalian lineages and may represent convergent evolution. Our analyses of the zebra finch MHC suggest a complex history involving chromosomal fission, gene duplication and translocation in the history of the MHC in birds, and highlight striking differences in MHC structure and organization among avian lineages.

Item Type: Article
Subjects: Q Science
Divisions: Faculties > Sciences > School of Biosciences
Depositing User: Darren Griffin
Date Deposited: 06 Jun 2013 09:44 UTC
Last Modified: 18 Jul 2014 14:04 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/34156 (The current URI for this page, for reference purposes)
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