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Zoological Science
Abstract
The major histocompatibility complex (MHC) includes many genes that are essential for the adaptive immune system, and variation in the antigen binding site (ABS) is related to resistance against pathogens. In the present study, quantitative real-time PCR indicated a larger number of MHC gene copies in the endangered population of Blakiston's fish owl (Bubo blakistoni) than in five other owl species, and massively parallel pyrosequencing detected more MHC class IIβ per individual alleles in B. blakistoni than in the other species. A chromosomal fluorescence in situ hybridization (FISH) analysis showed that the MHC class I and class IIβ loci are closely linked on a single pair of microchromosomes, indicating that the MHC genes were tandemly duplicated in a limited chromosomal region. Because B. blakistoni has twice as many MHC genes as its sister species, the tawny fish owl (Bubo flavipes), the duplication of MHC genes occurred after these species diverged by speciation. A Bayesian molecular phylogenetic analysis showed that the DAB1 and DAB2 lineages of MHC class IIβ alleles from various strigid species each formed a separate clade, indicating that the two allelic lineages preceded the radiation of Strigidae and evolved as paralogs. By contrast, the ABS sequences did not form distinct clades between DAB1 and DAB2 alleles but were intermixed, presumably due to gene conversion. Despite the low diversity of alleles per locus, B. blakistoni had many lineages of MHC class IIβ alleles. Gene duplication increases variation in the MHC genes in this species, and could have facilitated adaptation in small populations.
We thank Dr. Takeshi Takenaka, Ueno Zoological Gardens (Eri Okumura), Tama Zoological Park, and Sapporo Maruyama Zoo for providing samples. We obtained the samples through the Blakiston's fish owl conservation action program conducted by the Ministry of the Environment, Japan. This work was supported by a JSPS fellowship (grant number 25-1622) to K. Omote, and by the Environment Research and Technology Development Fund of the Ministry of the Environment, Japan (grant number D-1201). We thank Dr. Matthew H. Dick for editing the manuscript.
The authors have no competing interests to disclose.
KS and SF collected samples. CN cultured leukocytes, prepared chromosome samples, and mapped loci on chromosomes. KO conducted PCR, qPCR, cloning, sequencing, and phylogenetic analyses. TIK conducted massively parallel pyrosequencing. RM and KO wrote the paper, and all authors read and approved the final manuscript.
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