Hae III locus at Major Histocompatibility Complex (MHC) class II region hints duplicated DQA genes in Indian mithun (Bos frontalis)

Abstract

In bovines, duplication of major histocompatibility complex (MHC) class II DQ genes increase the advantage of high genetic polymorphism in the region multifold to produce better immune response and population fitness. In this study, the DQA gene duplication was explored at MHC class II locus in mithun (Bos frontalis, Bofr), a unique bovine of North-East region of India. A 776 nucleotide long genomic region encompassing hyper-variable exon 2 of Bofr-DQA was amplified in 79 mithuns and digested with Hae III restriction enzyme for PCR-RFLP analysis. The analysis revealed some of the restriction patterns, which were carrying the total fragment size of the alleles aggregating more than a heterozygous condition. Colony PCR-RFLP of clones of mithun DQA by Hinf I enzyme revealed a total of three DQA alleles in single PCR product. The RFLP of direct PCR and clone (colony) PCR products indicated the amplification of three DQA alleles at a time, suggesting duplication of the DQA locus in mithun. Further, the RFLP based typing of mithun DQA locus revealed the presence of five different DQA1 and DQA2 alleles in different combinations during duplication in mithun population. The duplication of DQA, carrying both DQA1 and DQA2 alleles gene was found to be present in nearly half of the mithun population. In mithun, similar to other bovines, DQA gene duplication may have much importance in creating more and diversified MHC class II molecules, thus conferring an advantage to bind with a more number of pathogenic antigens.