National Centre for Biosystematics, Natural History Museum, University of Oslo, Blindern, Oslo, Norway.
J Evol Biol. 2010 Jun 1;23(6):1206-17. doi: 10.1111/j.1420-9101.2010.01999.x. Epub 2010 Apr 23.
The genes of the major histocompatibility complex (MHC) are important model genes for understanding selective forces in evolution. Here, we document, using a cloning and sequencing approach, high polymorphism at the exon 2 of the MHC class II B (MHCIIB) genes in the bluethroat (Luscinia svecica); a minimum of 61 unique alleles were detected in 20 individuals, and at least 11 functional loci. In addition, several pseudogenes were revealed. The specimens originated from three different bluethroat subspecies (azuricollis, cyanecula and svecica), and we also analysed four specimens of the closely related thrush nightingale (L. luscinia) for comparison. Phylogenetic analyses of the functional alleles revealed 258 equally parsimonious trees with poor statistical support for the majority of nodes. The distribution of the sequences in the trees point to an ancestral origin of the polymorphism in MHC class II B genes, a portion of which predated the phylogenetic split between the bluethroat and the thrush nightingale. Strong signatures of balancing selection were uncovered for the codons coding for the peptide-binding residues of the functional MHCIIB exon 2 alleles. Our results highlight the importance of duplication and recombination events for shaping passerine MHC and give insights in the evolutionary dynamics of MHC variation among closely related taxa.
主要组织相容性复合体（MHC）的基因是理解进化中选择压力的重要模式基因。在这里，我们通过克隆和测序方法记录了蓝喉歌鸲（Luscinia svecica）MHC II B（MHCIIB）基因外显子 2 的高度多态性；在 20 个个体中检测到至少 61 个独特等位基因，至少 11 个功能基因座。此外，还揭示了几个假基因。这些标本来自三个不同的蓝喉亚种（azuricollis、cyanecula 和 svecica），我们还分析了四个密切相关的画眉夜莺（L. luscinia）标本进行比较。对功能等位基因的系统发育分析揭示了 258 棵具有相同简约性的树，大多数节点的统计支持度较差。这些序列在树中的分布表明 MHC II B 基因的多态性具有祖先起源，其中一部分发生在蓝喉歌鸲和画眉夜莺的系统发育分裂之前。在编码功能 MHCIIB 外显子 2 等位基因肽结合残基的密码子中发现了强烈的平衡选择信号。我们的研究结果强调了复制和重组事件对塑造雀形目 MHC 的重要性，并深入了解了密切相关类群中 MHC 变异的进化动态。
