Livestock Infectious Disease Programme, Institute for Animal Health, Compton RG20 7NN, UK.
Immunogenetics. 2012 Jun;64(6):435-45. doi: 10.1007/s00251-012-0612-6. Epub 2012 Mar 28.
Six major histocompatibility complex (MHC) classical class I genes have been identified in cattle, and up to three of these are expressed in variable combinations on different haplotypes. The origin and functional significance of this genetic complexity is unknown. However, an improved assembly of the cattle genome, an expanded database of full-length cDNA sequences and high-resolution frequency data concerning expressed class I genes in an economically important cattle breed combine to provide a new opportunity to study the significance of cattle MHC class I diversity. Analysis of these new data supports assignment of alleles to six discrete genes and further shows that all these classical genes share a common ancestor with a single non-classical gene, NC1. While haplotype structure is variable, with thirteen gene configurations identified, there are nevertheless clear constraints relating to both the number and combination of genes. Haplotypes expressing two classical genes are most frequently observed, and the classical class I gene 2 is almost invariably present. The frequency data support the dominance of gene 2, showing that close to 100 % of individuals carry at least one copy. This indicates a hierarchy in the functional importance of particular genes and haplotype structures. Haplotype frequency in cattle populations is therefore likely to impact on differential disease susceptibilities. This knowledge will be important for development of informed breeding strategies aimed at increasing the ability of cattle to survive in the face of future unpredictable pathogen exposure.
牛有六个主要组织相容性复合体(MHC)经典 I 类基因,其中多达三个以不同单倍型的可变组合表达。这种遗传复杂性的起源和功能意义尚不清楚。然而,牛基因组的组装得到了改进,全长 cDNA 序列的数据库得到了扩展,并且在一个具有重要经济意义的牛品种中有关表达的 I 类基因的高分辨率频率数据的结合,为研究牛 MHC I 类多样性的意义提供了新的机会。对这些新数据的分析支持将等位基因分配给六个离散的基因,并进一步表明所有这些经典基因都与单个非经典基因 NC1 具有共同的祖先。尽管单倍型结构具有可变性,有十三种基因构型被确定,但在基因数量和组合方面仍然存在明确的限制。表达两个经典基因的单倍型最为常见,并且经典 I 类基因 2 几乎总是存在。频率数据支持基因 2 的优势,表明接近 100%的个体至少携带一个拷贝。这表明特定基因和单倍型结构的功能重要性存在等级制度。因此,牛种群中单倍型的频率可能会影响疾病易感性的差异。这些知识对于制定明智的育种策略以提高牛在未来不可预测的病原体暴露面前的生存能力非常重要。