Evolution of major histocompatibility complex class I and class II genes in the brown bear

Abstract Background Major histocompatibility complex (MHC) proteins constitute an essential component of the vertebrate immune response, and are coded by the most polymorphic of the vertebrate genes. Here, we investigated sequence variation and evolution of MHC class I and class II DRB, DQA and DQB...

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Bibliographic Details
Published in:BMC Evolutionary Biology
Main Authors: Kuduk Katarzyna, Babik Wiesław, Bojarska Katarzyna, Śliwińska Ewa B, Kindberg Jonas, Taberlet Pierre, Swenson Jon E, Radwan Jacek
Format: Article in Journal/Newspaper
Language:English
Published: BMC 2012
Subjects:
Positive selection
Antigen binding sites
MHC gene expression
Phylogenetic analysis
Orthology
Ursidae
Evolution
QH359-425
Ursus arctos
Online Access:https://doi.org/10.1186/1471-2148-12-197
https://doaj.org/article/8e5c3a130d3f417d9eeb111f232cfaa8
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Summary:Abstract Background Major histocompatibility complex (MHC) proteins constitute an essential component of the vertebrate immune response, and are coded by the most polymorphic of the vertebrate genes. Here, we investigated sequence variation and evolution of MHC class I and class II DRB, DQA and DQB genes in the brown bear Ursus arctos to characterise the level of polymorphism, estimate the strength of positive selection acting on them, and assess the extent of gene orthology and trans-species polymorphism in Ursidae . Results We found 37 MHC class I, 16 MHC class II DRB, four DQB and two DQA alleles. We confirmed the expression of several loci: three MHC class I, two DRB, two DQB and one DQA. MHC class I also contained two clusters of non-expressed sequences. MHC class I and DRB allele frequencies differed between northern and southern populations of the Scandinavian brown bear. The rate of nonsynonymous substitutions (d N ) exceeded the rate of synonymous substitutions (d S ) at putative antigen binding sites of DRB and DQB loci and, marginally significantly, at MHC class I loci. Models of codon evolution supported positive selection at DRB and MHC class I loci. Both MHC class I and MHC class II sequences showed orthology to gene clusters found in the giant panda Ailuropoda melanoleuca . Conclusions Historical positive selection has acted on MHC class I, class II DRB and DQB, but not on the DQA locus. The signal of historical positive selection on the DRB locus was particularly strong, which may be a general feature of caniforms. The presence of MHC class I pseudogenes may indicate faster gene turnover in this class through the birth-and-death process. South–north population structure at MHC loci probably reflects origin of the populations from separate glacial refugia.

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