Distribution of ancient α1 and α2 domain lineages between two classical MHC class I genes and their alleles in grass carp
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.
KeywordsFish MHC class I Evolution Lineage Recombination Polymorphism
Conceived and designed the experiments: N Zhang, and C Xia. To assist the sampling: L Ma, Z Qu, X Wei, and M Tang. Gene clone and analysis: Z Li, Y Jiang, N Zhang, and Z Liu. Provided the resources: M Tang and C Xia. Wrote the paper: Z Li. Reviewed the paper: N Zhang and C Xia. All authors approved the final version of the paper.
This work was supported by the 973 Project of the China Ministry of Science and Technology (Grant 2013CB835302), and the National Natural Science Foundation of China (Grant 31572653).
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