Evolution of Great Ape MHC Class I Genes
To investigate whether the classical HLA class I loci have been preserved in the great apes and to determine when the A/E recombination event took place, we have sequenced and expressed eight MHC class I gene products expressed by lymphocytes from an orangutan (Pongo pygmaeus) and a gibbon (Hylobates lar). Three different HLA-B-related gene products were found in the orangutan, suggesting that the ancestral homologue of the HLA-B locus had undergone a duplication in this species. Since the HLA-A homologues found in the orangutan and the gibbon were recombinants between the ancestors of HLA-A and HLA-E, the recombination event must have occurred before gibbons and humans last had a common ancestor. Thus, the A/E recombination event occurred over 38 million years ago. Preservation of HLA-A and -B homologues in orangutans and gibbons suggests that the HLA-A and -B loci are extremely stable and that recombination between them is rare. Furthermore, the data presented here strongly argue against the role of concerted evolution in the generation of diversity in great ape MHC class I molecules.
KeywordsMajor Histocompatibility Complex Recombination Event Concerted Evolution Pygmy Chimpanzee Pongo Pygmaeus
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