Selective forces shaping diversity in the class I region of the major histocompatibility complex in dairy cattle
Selective forces shaping diversity in the class I region of the major histocompatibility complex in dairy cattle
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DOI：
10.1111/j.1365-2052.2011.02239.x
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发表时间：
2012-06-01
期刊：
影响因子：
2.4
通讯作者：
Ellis, S. A.
中科院分区：
文献类型：
--
作者：
Codner, G. F.;Stear, M. J.;Ellis, S. A.
主要组织相容性复合体（MHC）是哺乳动物基因组中最多样化的区域之一。MHC基因的多样性是其在免疫系统中功能不可或缺的一部分，虽然病原体在形成这种多样性方面发挥了关键作用，但其他选择性力量的贡献仍不清楚。牛的控制饲养为识别和探索这些力量提供了一个很好的模式。我们的特点是MHC I类基因存在于加拿大荷斯坦A. I。公牛，并将结果与早期研究中获得的结果进行了比较。没有证据表明20年来MHC多样性减少，但一些单倍型的相对频率发生了变化：以前罕见的A12（w12B）单倍型与A15一起成为最常见的单倍型，而在早期样本中占主导地位的A19的频率显着降低。在目前的研究中，只有7%的公牛是MHC纯合子，而HardyWeinberg的预期为14%。为了确定在工作中的选择力，基因替代模型被用来计算MHC的选择性状的影响，估计育种值为每个bull.显着的MHC和生产，疾病和生育性状之间的关联进行了鉴定，这表明，MHC的多样性不仅仅是由疾病在这个受控的育种系统。减少一个共同的单倍型，纯合子公牛的数量减少，疾病和生产性状的协会一起表明，在奶牛的MHC多样性保持杂合子优势。
The major histocompatibility complex (MHC) is one of the most diverse regions of the mammalian genome. Diversity in MHC genes is integral to their function in the immune system, and while pathogens play a key role in shaping this diversity, the contribution of other selective forces remains unclear. The controlled breeding of cattle offers an excellent model for the identification and exploration of these forces. We characterized the MHC class I genes present in a sample of Canadian Holstein A.I. bulls and compared the results with those obtained in an earlier study. No evidence for a reduction in MHC diversity over 20 years was observed, but the relative frequency of some haplotypes had changed: the formerly rare A12 (w12B) haplotype had become the most common, together with A15, while A19, which dominated the earlier sample, had significantly reduced in frequency. Only 7% of bulls in the current study were MHC homozygous compared with the 14% expected under HardyWeinberg. To identify the selective forces at work, a gene substitution model was used to calculate the effects of MHC on selection traits using estimated breeding values for each bull. Significant associations between MHC and production, disease and fertility traits were identified, suggesting that MHC diversity is not merely shaped by disease in this controlled breeding system. The decrease in a common haplotype, the reduced number of homozygous bulls and the associations with disease and production traits together indicate that MHC diversity in dairy cattle is maintained by heterozygote advantage.