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Open Access Highly Accessed Research article

Directional and balancing selection in human beta-defensins

Edward J Hollox1 and John AL Armour2*

Author Affiliations

1 Department of Genetics, University of Leicester, Leicester, UK

2 Institute of Genetics, University of Nottingham, Nottingham, UK

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BMC Evolutionary Biology 2008, 8:113  doi:10.1186/1471-2148-8-113

Published: 16 April 2008

Abstract

Background

In primates, infection is an important force driving gene evolution, and this is reflected in the importance of infectious disease in human morbidity today. The beta-defensins are key components of the innate immune system, with antimicrobial and cell signalling roles, but also reproductive functions. Here we examine evolution of beta-defensins in catarrhine primates and variation within different human populations.

Results

We show that five beta-defensin genes that do not show copy number variation in humans show evidence of positive selection in catarrhine primates, and identify specific codons that have been under selective pressure. Direct haplotyping of DEFB127 in humans suggests long-term balancing selection: there are two highly diverged haplotype clades carrying different variants of a codon that, in primates, is positively selected. For DEFB132, we show that extensive diversity, including a four-state amino acid polymorphism (valine, isoleucine, alanine and threonine at position 93), is present in hunter-gatherer populations, both African and non-African, but not found in samples from agricultural populations.

Conclusion

Some, but not all, beta-defensin genes show positive selection in catarrhine primates. There is suggestive evidence of different selective pressures on these genes in humans, but the nature of the selective pressure remains unclear and is likely to differ between populations.