The Gene Duplication of Beta 2 Microglobulin and Protein Associated with Topoisomerase II Homolog 2 (PATL2) in Artiodactyla and Remains Intact Only in Pigs

From the analysis of the pig genome assembly SSC10.2, we discovered a segmental duplication of ~48kb in size containing the entire coding sequence of beta 2 microglobulin (B2M) and the protein associated with topoisomerase II homolog 2 (PATL2) genes on pig chromosome 1. Based on the finding, we evaluated the effect of the B2M duplication as a light subunit of the major histocompatibility complex (MHC) for the possible strengthening of immune capacity through the increasing of MHC expression on the pig cell surface.  As a first step, we confirmed the accuracy of the B2M duplication in the pig genome by PCR and direct sequencing of duplication boundaries. Subsequently, we also confirmed the copy number of B2M in the pig genome using real-time PCR at the level of mRNA and genomic DNA. We also analyzed and compared the synteny blocks of the corresponding region among pigs and other mammals to check the evolutionary conservation. Our results showed that this duplication may have been occurred during the speciation of artiodactyla but remains intact only in pigs. In addition, we evaluated the protein level of MHC expression on cell surface after transfecting B2M cDNA to a pig cell line. However, the protein level was similar to that of before transfection in our analysis. Although the functional effect of B2M duplication in pigs is still unclear, this may provide beneficial effect to immune reaction including tumor regression in pigs. More detail analyses are necessary to address this interesting question.