Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing, China.
J Hered. 2019 May 7;110(3):332-339. doi: 10.1093/jhered/esz005.
Cetaceans are a suborder of secondarily adapted aquatic mammals with an enigmatic history involving a transition from land to sea approximately 55 Mya. During the transition period, cetaceans would have faced many new pathogen challenges, but limited information is available about the adaptive immune system of these mammals. The major histocompatibility complex (MHC) family plays a key role in antigen recognition and presentation in adaptive immunity, which is believed to have evolved in response to pathogens. In the present study, MHC class II loci were characterized in 7 published cetacean genome assemblies and the genomic organization of cetaceans was compared with that of their terrestrial relatives, the cow, sheep, and pig. A total of 9 MHC class II loci were identified in the cetacean genomes: DRA, DRB, DQA, DQB, DPB, DOA, DOB, DMA, and DMB. Sequences from 8 of the 9 genes included intact coding regions and were presumably functional. The organization of the MHC class II loci was conserved across the examined mammalian species, whereas the orientation and number of the alpha and beta genes varied among the species. The phylogenetic reconstruction of all MHC genes from Cetartiodactyla suggested that alpha and beta genes had different topologies. Additionally, based on a phylogenetic reconstruction of the multi-locus DRB, 2 (DRB1 and DRB2) of the 4 putative gene copies were hypothesized to have duplicated and evolved during the radiation of cetaceans.
鲸目动物是次生适应水生哺乳动物的一个亚目，其历史神秘，涉及大约 5500 万年前从陆地到海洋的过渡。在过渡时期，鲸目动物将面临许多新的病原体挑战，但关于这些哺乳动物适应性免疫系统的信息有限。主要组织相容性复合体 (MHC) 家族在适应性免疫中的抗原识别和呈递中发挥着关键作用，据信它是为了应对病原体而进化的。在本研究中，对 7 个已发表的鲸目动物基因组组装中的 MHC 类 II 基因座进行了特征描述，并比较了鲸目动物与它们的陆地近亲牛、绵羊和猪的基因组组织。在鲸目动物基因组中总共鉴定出 9 个 MHC 类 II 基因座：DRA、DRB、DQA、DQB、DPB、DOA、DOB、DMA 和 DMB。这 9 个基因中的 8 个序列都包含完整的编码区，推测具有功能。所检查的哺乳动物物种的 MHC 类 II 基因座的组织是保守的，而 alpha 和 beta 基因的取向和数量在物种间有所不同。所有鲸目动物 MHC 基因的系统发育重建表明，alpha 和 beta 基因具有不同的拓扑结构。此外，基于对多基因座 DRB 的系统发育重建，4 个假定基因拷贝中的 2 个（DRB1 和 DRB2）被假设在鲸目动物的辐射过程中发生了复制和进化。
