Characterization, Polymorphism and Selection of Major Histocompatibility Complex (MHC) DAB Genes in Vulnerable Chinese Egret (Egretta eulophotes)

Zeng Wang,Wenzhen Fang,Xiaolin Chen,Qingxian Lin,Xiaoping Zhou

doi:10.1371/journal.pone.0074185

Abstract

The major histocompatibility complex (MHC) is an excellent molecular marker for the studies of evolutionary ecology and conservation genetics because it is a family of highly polymorphic genes that play a key role in vertebrate immune response. In this study, the functional genes of MHC Class II B (DAB) were isolated for the first time in a vulnerable species, the Chinese egret ( Egretta eulophotes ). Using a full length DNA and cDNA produced by PCR and RACE methods, four potential MHC DAB loci were characterized in the genome of this egret and all four were expressed in liver and blood. At least four copies of the MHC gene complex were similar to two copies of the minimal essential MHC complex of chicken, but are less complex than the multiple copies expressed in passerine species. In MHC polymorphism, 19 alleles of exon 2 were isolated from 48 individuals using PCR. No stop codons or frameshift mutations were found in any of the coding regions. The signatures of positive selection detected in potential peptide-binding regions by Bayesian analysis, suggesting that all of these genes were functional. These data will provide the fundamental basis for further studies to elucidate the mechanisms and significance of MHC molecular adaptation in vulnerable Chinese egret and other ardeids.

Highlights

The major histocompatibility complex (MHC) is a multi-gene family, representing an important component in the acquired immune system of the vertebrate species
The MHC class II genes consists of two genes, named A and B, in which the B genes are responsible for the majority of the polymorphism
DNA sequences of four different MHC DAB genes were isolated from one individual Chinese egret, which was highly similar over large stretches but distinguished by the divergent intron 1

Summary

Introduction

The major histocompatibility complex (MHC) is a multi-gene family, representing an important component in the acquired immune system of the vertebrate species. Studies on the functional genes of MHC II B (DAB) complex in birds have indicated that multiple copies of these genes are highly variable among different species [5,7,8,9,10,11,12,13,14,15,16,17,18]. The most complex of the MHC structures were found in passerine birds [19,20,21] while the “minimal essential” structures were found in a non-passerine bird, the red jungle fowl (Galliformes, Phasianidae, Gallus gallus) [22,23]. Other non-passerine birds, including raptors and seabirds, paleognath birds, and penguins have been reported to have more complex MHC structures than the “minimal essential” genes [24]

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