Kosch Tiffany A, Eimes John A, Didinger Chelsea, Brannelly Laura A, Waldman Bruce, Berger Lee, Skerratt Lee F
One Health Research Group, College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland, 4811, Australia.
Faculty of Veterinary and Agricultural Sciences, University of Melbourne, Victoria, 3010, Australia.
Immunogenetics. 2017 Mar;69(3):165-174. doi: 10.1007/s00251-016-0965-3. Epub 2016 Dec 27.
Southern corroboree frogs (Pseudophryne corroboree) have declined to near extinction in the wild after the emergence of the amphibian chytrid fungus Batrachochytrium dendrobatidis in southeastern Australia in the 1980s. A major captive breeding and reintroduction program is underway to preserve this iconic species, but improving resistance to B. dendrobatidis would help the wild population to be self-sustaining. Using 3' and 5' rapid amplification of complementary DNA ends (RACE), we characterized the major histocompatibility complex (MHC) class IA locus in this species. We then used sequences generated from RACE to design primers to amplify the peptide-binding region (PBR) of this functional genetic marker. Finally, we analysed the diversity, phylogeny, and selection patterns of PBR sequences from four P. corroboree populations and compared this with other amphibian species. We found moderately high MHC class IA genetic diversity in this species and evidence of strong positive and purifying selection at sites that are associated with putative PBR pockets in other species, indicating that this gene region may be under selection for resistance to Bd. Future studies should focus on identifying alleles associated with Bd resistance in P. corroboree by performing a Bd laboratory challenge study to confirm the functional importance of our genetic findings and explore their use in artificial selection or genetic engineering to increase resistance to chytridiomycosis.
自20世纪80年代澳大利亚东南部出现两栖类壶菌——蛙壶菌（Batrachochytrium dendrobatidis）以来，南部灌丛蛙（Pseudophryne corroboree）在野外数量已减少至几近灭绝。目前正在开展一项大型圈养繁殖和重新引入计划以保护这一标志性物种，但提高对蛙壶菌的抗性将有助于野生种群实现自我维持。我们利用3'和5'互补DNA末端快速扩增技术（RACE），对该物种的主要组织相容性复合体（MHC）IA类基因座进行了表征。然后，我们利用RACE产生的序列设计引物，以扩增这个功能基因标记的肽结合区域（PBR）。最后，我们分析了来自四个南部灌丛蛙种群的PBR序列的多样性、系统发育和选择模式，并将其与其他两栖类物种进行了比较。我们发现该物种的MHC IA类基因具有中等程度的高遗传多样性，并且在与其他物种假定的PBR口袋相关的位点上存在强烈的正选择和纯化选择的证据，这表明该基因区域可能因对蛙壶菌的抗性而受到选择。未来的研究应集中于通过进行蛙壶菌实验室挑战研究，来鉴定南部灌丛蛙中与抗蛙壶菌相关的等位基因，以确认我们遗传研究结果的功能重要性，并探索其在人工选择或基因工程中的应用，以提高对壶菌病的抗性。
