Allelic variation, balancing selection and positive selected sites detected from MHC class I alpha gene of olive flounder

摘要

Major histocompatibility complex (MHC) genes play an important role in the immune response of vertebrates. Allelic polymorphism and pattern of evolution in MHC genes has been investigated in many mammals, however, much less is known in teleost. In the present study, we have investigated complete MHC I alpha gene consists of 7 exons and 6 introns in Olive flounder (Paralichthys olivaceus). Genetic variation in the MHC class I alpha gene was also tested in flounder. In 32 individuals, a total of 62 alleles were detected from exon 2 of MHC class I alpha gene. The rate of non-synonymous substitutions (d sub( )N occurred at a significantly higher frequency than that of synonymous substitutions (d sub( )S in PBR and non-PBR, suggesting that balancing selection for maintaining polymorphisms at the MHC I alpha locus. Many positive selection sites were found to act very intensively on antigen binding sites. Our founding suggests a snapshot in an evolutionary process of MHC I alpha gene evolution of the P. olivaceus.