Bartocillo Aye Mee F, Nishita Yoshinori, Abramov Alexei V, Masuda Ryuichi
Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, 060-0810 Japan.
Department of Biological Sciences, Faculty of Science, Hokkaido University, Kita 10, Nishi 8, Kita-Ku, Sapporo, 060-0810 Japan.
Mamm Res. 2021;66(2):371-383. doi: 10.1007/s13364-021-00561-y. Epub 2021 Mar 15.
Major histocompatibility complex (MHC) genes have been widely studied to assess the immunological fitness and evolutionary adaptation of animal populations. Among the Canidae, the raccoon dog's adventurous nature, omnivorous behavior, and high variability of intracellular pathogens make it ideal to study selection on MHC class I in a non-model canid species. Here, we examined allelic diversity and evolutionary patterns of MHC class I genes in the raccoon dog (). We identified 48 novel MHC class I alleles from 31 raccoon dogs from Japan and Russia. Some alleles were geographically restricted, whereas others were widely distributed across the species' range. The rate of non-synonymous substitutions was greater than that of synonymous substitutions for both exon 2 and exon 3 encoding α1 and α2 domains, respectively, in the α chain of the MHC class I protein. Positively selected sites at the amino acid level were evident in both the α1 and α2 domains, and a recombination breakpoint was found in exon 3. Bayesian phylogenetic trees showed no evidence of trans-species polymorphism (TSP) with alleles from carnivoran species in other families but did detect TSP between raccoon dogs and the domestic dog, , indicative of long-term balancing selection in canids. Our results indicate that the extensive allelic diversity of MHC class I in Japanese and Russian raccoon dogs has been influenced and maintained by pathogen-driven positive selection, recombination, and long-term balancing selection.
The online version contains supplementary material available at 10.1007/s13364-021-00561-y.
主要组织相容性复合体（MHC）基因已被广泛研究，以评估动物种群的免疫适应性和进化适应性。在犬科动物中，貉的冒险天性、杂食行为以及细胞内病原体的高度变异性，使其成为研究非模式犬科物种MHC I类选择的理想对象。在这里，我们研究了貉MHC I类基因的等位基因多样性和进化模式。我们从来自日本和俄罗斯的31只貉中鉴定出48个新的MHC I类等位基因。一些等位基因在地理上受到限制，而其他等位基因则广泛分布于该物种的分布范围内。在MHC I类蛋白α链中分别编码α1和α2结构域的外显子2和外显子3中，非同义替换率均高于同义替换率。在α1和α2结构域中均发现了氨基酸水平上的正选择位点，并且在外显子3中发现了一个重组断点。贝叶斯系统发育树显示，与其他科食肉动物物种的等位基因没有跨物种多态性（TSP）的证据，但确实检测到貉与家犬之间存在TSP，这表明犬科动物中存在长期的平衡选择。我们的结果表明，日本和俄罗斯貉中MHC I类的广泛等位基因多样性受到病原体驱动的正选择、重组和长期平衡选择的影响并得以维持。
在线版本包含可在10.1007/s13364-021-00561-y获取的补充材料。
