Department of Biodiversity Studies and Bioeducation, Faculty of Biology and Environmental Protection, University of Łódź, Banacha 1/3, 90-237, Łódź, Poland.
Sci Rep. 2022 Apr 29;12(1):7031. doi: 10.1038/s41598-022-11018-w.
Genes of the Major Histocompatibility Complex (MHC) form a key component of vertebrate adaptive immunity, as they code for molecules which bind antigens of intra- and extracellular pathogens (MHC class I and II, respectively) and present them to T cell receptors. In general, MHC genes are hyper-polymorphic and high MHC diversity is often maintained within natural populations (via balancing selection) and within individuals (via gene duplications). Because of its complex architecture with tandems of duplicated genes, characterization of MHC region in non-model vertebrate species still poses a major challenge. Here, we combined de novo genome assembly and high-throughput sequencing to characterize MHC polymorphism in a rallid bird species, the Eurasian coot Fulica atra. An analysis of genome assembly indicated high duplication rate at MHC-I, which was also supported by targeted sequencing of peptide-binding exons (at least five MHC-I loci genotyped). We found high allelic richness at both MHC-I and MHC-II, although signature of diversifying selection and recombination (gene conversion) was much stronger at MHC-II. Our results indicate that Eurasian coot retains extraordinary polymorphism at both MHC classes (when compared to other non-passerine bird species), although they may be subject to different evolutionary mechanism.
主要组织相容性复合体（MHC）基因是脊椎动物适应性免疫的关键组成部分，因为它们编码的分子可以结合细胞内和细胞外病原体的抗原（分别为 MHC I 和 II），并将其呈递给 T 细胞受体。一般来说，MHC 基因高度多态性，自然种群（通过平衡选择）和个体内（通过基因重复）通常维持高 MHC 多样性。由于其具有串联重复基因的复杂结构，非模式脊椎动物物种 MHC 区域的特征仍然是一个主要挑战。在这里，我们结合从头基因组组装和高通量测序来描述欧亚黑水鸡 Fulica atra 这一涉水鸟类的 MHC 多态性。基因组组装分析表明 MHC-I 具有很高的重复率，这也得到了肽结合外显子靶向测序（至少五个 MHC-I 基因座基因型）的支持。我们发现 MHC-I 和 MHC-II 的等位基因丰富度都很高，尽管 MHC-II 的多样化选择和重组（基因转换）的特征要强得多。我们的研究结果表明，与其他非雀形目鸟类物种相比，欧亚黑水鸡在 MHC 两类中都保留了非凡的多态性，尽管它们可能受到不同的进化机制的影响。
