Diversity and selection of MHC class I genes in the vulnerable Chinese egret (Egretta eulophotes).

Zeng Wang,Wenzhen Fang,Tzen-Yuh Chiang,Xiaolin Chen,Qingxian Lin,Xiaoping Zhou

doi:10.1371/journal.pone.0176671

Abstract

The genes of major histocompatibility complex (MHC) are important to vertebrate immune system. In this study, two new MHC class I genes, designated as Egeu-UAA and Egeu-UBA, were discovered in the vulnerable Chinese egret (Egretta eulophotes). Using a full length DNA and cDNA produced by PCR and RACE methods, these two MHC class I loci were characterized in the genome of the Chinese egret and were also found to be expressed in liver and blood. Both new genes showed the expected eight exons and were similar to two copies of the minimal essential MHC complex of chicken. In genetic diversity, 14 alleles (8 for UAA and 6 for UBA) in the MHC class I gene exon 3 were found in 60 individuals using locus-specific primers and showed little polymorphism. Only three potential amino acid residues were detected under positive selection in potential peptide-binding regions (PBRs) by Bayesian analysis. These new results provide the fundamental basis for further studies to elucidate the molecular mechanisms and significance of MHC molecular adaptation in vulnerable Chinese egret and other ardeids, finding that have not been previously reported.

Highlights

The major histocompatibility complex (MHC) is a gene complex that encodes for cell-surface proteins responsible for the recognition and presentation of foreign antigens to T-lymphocytes, and which triggers the adaptive branch of the immune system [1]
MHC class II molecules present peptides that arise in intracellular vesicles and extracellular space
This study aims to: (1) isolate full genomic and cDNA MHC class I sequences from the Chinese egret (Egretta eulophotes), (2) design locus-specific primers to survey the variation in peptide-binding regions (PBRs)-encoding exons for all loci and (3) gain insights into the selection pressures acting on PBR and non-PBR regions within the third exon of MHC class I loci in the Chinese egret

Summary

Introduction

The major histocompatibility complex (MHC) is a gene complex that encodes for cell-surface proteins responsible for the recognition and presentation of foreign antigens to T-lymphocytes, and which triggers the adaptive branch of the immune system [1]. Class II molecules are involved in the adaptive immune response, but class I is recognised by T cells of the adaptive immune system and NK cells of the innate immune system. Some genes in the class III region encode molecules involved in lymphocyte interactions or with innate immunity. MHC class I molecules function to present peptides that arise from proteins expressed in the cytoplasm to contiguous organelles including the nucleus (often derived from what are referred to as intracellular pathogens). MHC class II molecules present peptides that arise in intracellular vesicles and extracellular space (often derived from what are referred to as extracellular pathogens). Since each MHC molecule can successfully bind a limited number of peptides, greater

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