Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3FL, UK.
Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, Midlothian, EH26 OPZ, UK.
Immunogenetics. 2019 May;71(5-6):383-393. doi: 10.1007/s00251-019-01109-w. Epub 2019 Feb 22.
The ovine MHC class IIa is known to consist of six to eight loci located in close proximity on chromosome 20, forming haplotypes that are typically inherited without recombination. Here, we characterise the class IIa haplotypes within the Soay sheep (Ovis aries) on St. Kilda to assess the diversity present within this unmanaged island population. We used a stepwise sequence-based genotyping strategy to identify alleles at seven polymorphic MHC class IIa loci in a sample of 118 Soay sheep from four cohorts spanning 15 years of the long-term study on St. Kilda. DRB1, the most polymorphic MHC class II locus, was characterised first in all 118 sheep and identified six alleles. Using DRB1 homozygous animals, the DQA (DQA1, DQA2 and DQA2-like) and DQB (DQB1, DQB2 and DQB2-like) loci were sequenced, revealing eight haplotypes. Both DQ1/DQ2 and DQ2/DQ2-like haplotype configurations were identified and a single haplotype carrying three DQB alleles. A test sample of 94 further individuals typed at the DRB1 and DQA loci found no exceptions to the eight identified haplotypes and a haplotype homozygosity of 21.3%. We found evidence of historic positive selection at DRB1, DQA and DQB. The limited variation at MHC class IIa loci in Soay sheep enabled haplotype characterisation but showed that no single locus could capture the full extent of the expressed variation in the region.
绵羊 MHC IIa 类基因座已知由位于 20 号染色体上的六个到八个紧密相邻的基因座组成，形成通常不发生重组的单体型。在这里，我们对圣基尔达的斯凯岛绵羊（Ovis aries）中的 IIa 类单体型进行了特征分析，以评估这个未经管理的岛屿种群中存在的多样性。我们使用逐步序列基因为七个多态性 MHC IIa 基因座的等位基因进行了分型，在跨越圣基尔达长期研究 15 年的四个队列中，对 118 只斯凯岛绵羊的样本进行了分析。DRB1 是最具多态性的 MHC II 基因座，首先在所有 118 只绵羊中进行了特征分析，并确定了 6 个等位基因。使用 DRB1 纯合动物，对 DQA（DQA1、DQA2 和 DQA2-like）和 DQB（DQB1、DQB2 和 DQB2-like）基因座进行了测序，揭示了 8 种单体型。既鉴定到了 DQ1/DQ2 也鉴定到了 DQ2/DQ2-like 单体型构型，还有一个单体型携带三个 DQB 等位基因。对 94 个进一步在 DRB1 和 DQA 基因座进行了分型的测试样本进行了分析，没有发现 8 种鉴定出的单体型和 21.3%的单体型纯合性之外的异常情况。我们发现了 DRB1、DQA 和 DQB 处的历史上正选择的证据。斯凯岛绵羊 MHC IIa 基因座的有限变异使单体型特征分析成为可能，但表明没有单个基因座能够捕获该区域表达变异的全部范围。
