Major histocompatibility complex (MHC) class I molecules play a crucial role in the immune response by binding and presenting pathogen-derived peptides to specific CD8+ T cells. From cDNA of 20 individuals of wild grass carp (Ctenopharyngodon idellus), we could amplify one or two alleles each of classical MHC class I genes Ctid-UAA and Ctid-UBA. In total, 27 and 22 unique alleles of Ctid-UAA and Ctid-UBA were found. The leader, α1, transmembrane and cytoplasmic regions distinguish between Ctid-UAA and Ctid-UBA, and their encoded α1 domain sequences belong to the ancient lineages α1-V and α1-II, respectively, which separated several hundred million years ago. However, Ctid-UAA and Ctid-UBA share allelic lineage variation in their α2 and α3 sequences, in a pattern suggestive of past interlocus recombination events that transferred α2+α3 fragments. The allelic Ctid-UAA and Ctid-UBA variation involves ancient variation between domain lineages α2-I and α2-II, which in the present study was dated back to before the ancestral separation of teleost fish and spotted gar (> 300 million years ago). This is the first report with compelling evidence that recombination events combining different ancient α1 and α2 domain lineages had a major impact on the allelic variation of two different classical MHC class I genes within the same species.

中文翻译：

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草鱼中两个经典的MHC I类基因及其等位基因之间古代α1和α2结构域谱系的分布。

主要的组织相容性复合体（MHC）I类分子通过将病原体衍生的肽结合并呈递给特定的CD8 + T细胞，在免疫反应中发挥关键作用。从野生草鱼（Ctenopharyngodon idellus）的20个个体的cDNA中，我们可以扩增一个或两个等位基因，分别是经典的MHC I类基因Ctid-UAA和Ctid-UBA。总共发现了Ctid-UAA和Ctid-UBA的27和22个独特等位基因。前导区α1，跨膜区和胞质区区分Ctid-UAA和Ctid-UBA，它们编码的α1结构域序列分别属于古老的谱系α1-V和α1-II，它们分开了几亿年前。然而，Ctid-UAA和Ctid-UBA在其α2和α3序列中共有等位基因谱系变异，其模式暗示了过去转移α2+α3片段的基因间重组事件。等位基因Ctid-UAA和Ctid-UBA变异涉及域谱系α2-I和α2-II之间的古老变异，在本研究中，该变异可追溯到硬骨鱼和斑的祖先分离之前（> 3亿年前） 。这是第一份有力证据的报告，表明结合不同的古代α1和α2结构域谱系的重组事件对同一物种内两个不同的经典MHC I类基因的等位基因变异具有重大影响。