oa Major Histocompatibility Complex Genes Of The Dromedary Camel

The Major Histocompatibility Complex (MHC) is a genetic region involved in many aspects of immune responses, including the processing and presentation of antigenic peptides to T cells. The MHC, which spans approximately 4 million base pairs, is gene dense and contains many duplicated, highly polymorphic genes, particularly those encoding the MHC class I and class II molecules. Evidence for increased fitness of MHC heterozygotes over homozygotes has been observed in several species; this has usually been associated with resistance to infectious diseases. Studies of the MHC of many mammalian species have established a general plan for the genomic organization of this region, but they have also identified differences that are important to our understanding of the evolution and function of the MHC and its role in immune defense. As examples, the MHC region in some species is characterized by Copy Number Variants between haplotypes, while in certain species the level of polymorphism is limited. Given the cultural and economic importance of the Arabian camel (Camelus dromedarius) in North Africa and throughout the Middle East for meat, milk, transport, and sport, it is surprising that few genetic studies of this species have been reported, and none on the Major Histocompatibility Complex. Here we used DNA sequence data from a recent publication on the Bactrian camel (Camelus bactrianus) genome (Jirimutu et al., Nature Communications, 3:1202, 2012) and limited RNA sequence data from Expressed Sequence Tags (ESTs) of the dromedary camel deposited in the US NIH NCBI database http://www.ncbi.nlm.nih.gov/bioproject/82161. We identified microsatellite repeats located in the MHC class I and class II regions of the Bactrian camel genome and designed Polymerase Chain Reaction (PCR) primers in flanking DNA that were tested on a DNA sample from a Qatari dromedary camel. The primers amplified DNA from the dromedary camel sample and demonstrated microsatellite heterozygosity in the sample tested in both the MHC class I and class II regions. Using ESTs from the NCBI dromedary database we designed PCR primers in conserved regions of camel MHC class I and II genes to amplify MHC class I and class II gene fragments from the dromedary sample. The amplified fragments were purified, cloned, and sequenced. The sequences were not identical, demonstrating variation in both MHC class I and class II structural genes. This study demonstrates the feasibility of using Bactrian camel DNA sequence to design gene probes for the dromedary camel. The molecular probes we have developed can be used to estimate heterozygosity within the MHC of the dromedary camel as part of a full characterization of the genome of this species. This study is part of a new project on comparative genomics of the Arabian horse, the dromedary camel, and the Arabian oryx recommended for funding by the Qatar National Research Foundation (award pending). The project involves scientists from several units of Cornell University, including Weill-Cornell Medical College - Doha, and local stakeholders in Qatar.