The major histocompatibility complex in Old World camelids and low polymorphism of its class II genes

Abstract

BackgroundThe Major Histocompatibility Complex (MHC) is a genomic region containing genes with crucial roles in immune responses. MHC class I and class II genes encode antigen-presenting molecules expressed on the cell surface. To counteract the high variability of pathogens, the MHC evolved into a region of considerable heterogeneity in its organization, number and extent of polymorphism. Studies of MHCs in different model species contribute to our understanding of mechanisms of immunity, diseases and their evolution. Camels are economically important domestic animals and interesting biomodels. Three species of Old World camels have been recognized: the dromedary (Camelus dromedarius), Bactrian camel (Camelus bactrianus) and the wild camel (Camelus ferus). Despite their importance, little is known about the MHC genomic region, its organization and diversity in camels. The objectives of this study were to identify, map and characterize the MHC region of Old World camelids, with special attention to genetic variation at selected class MHC II loci.ResultsPhysical mapping located the MHC region to the chromosome 20 in Camelus dromedarius. Cytogenetic and comparative analyses of whole genome sequences showed that the order of the three major sub-regions is “Centromere - Class II – Class III – Class I”. DRA, DRB, DQA and DQB exon 2 sequences encoding the antigen binding site of the corresponding class II antigen presenting molecules showed high degree of sequence similarity and extensive allele sharing across the three species. Unexpectedly low extent of polymorphism with low numbers of alleles and haplotypes was observed in all species, despite different geographic origins of the camels analyzed. The DRA locus was found to be polymorphic, with three alleles shared by all three species. DRA and DQA sequences retrieved from ancient DNA samples of Camelus dromedarius suggested that additional polymorphism might exist.ConclusionsThis study provided evidence that camels possess an MHC comparable to other mammalian species in terms of its genomic localization, organization and sequence similarity. We described ancient variation at the DRA locus, monomorphic in most species. The extent of molecular diversity of MHC class II genes seems to be substantially lower in Old World camels than in other mammalian species. Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2500-1) contains supplementary material, which is available to authorized users.

The major histocompatibility complex of Old World camelids: Class I and class I‐related genes

“…We have previously characterized the overall genomic organization of the MHC region in camelids and studied selected MHC class II genes. We observed a rather low genetic diversity of this MHC sub‐region . The objective of this current study was to extend this knowledge on the MHC of two Old World camel species by annotating and characterizing selected MHC class I and class I‐related loci.…”

Advances in camel genomics and their applications: A review

“…The DRA locus was found to be polymorphic, with three alleles shared by all three species. The extent of molecular diversity of MHC class II genes seems to be substantially lower in Old World camels than in other mammalian species (Plasil et al 2016).…”

“…First draft whole genomes of the Old World camelids have recently been published (Jirimutu et al 2012;Burger and Palmieri 2014;Wu et al 2014Wu et al , 2015Almathen et al 2016;Fitak et al 2016). The assembled genome sizes were 2.01, 2.01 and 2.05 GB while the annotated genes were 20.…”

“…High blood glucose levels and a diet loaded with high salt are considered adaptation mechanisms that may help camels to survive in driest and harshest condition. The camel rapidly evolving genes include some that regulate insulin signaling pathways, salt metabolism and also duplications of genes which play critical roles in sodium reabsorption and water balance in the kidney (Jirimutu et al 2012;Burger and Palmieri 2014;Wu et al 2014Wu et al , 2015Almathen et al 2016;Fitak et al 2016). The identification of key genes involved in the adaptation to the desert environment may have applications in breeding programs and may provide some perspective for disease-resistance research in different animal species.…”

Modelling functional and structural impact of non-synonymous single nucleotide polymorphisms of the DQA1 gene of three Nigerian goat breeds

“…Sequencing of the DQA1 complementary DNA (cDNA) revealed a single 768 bp open reading frame consisting of four exons and encoding a 255 amino acid protein (Amills et al, 2005;Plasil et al, 2016). Among MHC genes, DRB and DQA are most polymorphic (Subramani et al, 2016).…”