Studies on the molecular evolution of MHC class I genes and their polymorphism

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The present study suggests that the essential features in the T cell recognition of the MHC class I molecule/peptide complex appear to have been established at the early stage of the vertebrate evolution. Our study revealed highly conserved nature of the MHC class I molecules, namely, conservation of the peptide-binding strategy and conservation of the interface between a T cell receptor and an MHC class I molecule. We also analysed the genomic structure of a cartilaginous fish classical MHC class I gene and found that the exon/intron organization of the classical MHC class I gene is, basically, highly conserved throughout the evolution of the jawed vertebrates. We further examined the linkage between the classical MHC class I and class II genes in the cartilaginous fish. The results indicated that the two MHC classes belong to the same linkage group in the genome of the cartilaginous fish in contrast to the teleost fish but in accordance with the other vertebrate groups such as mammals, birds, and amphibians. Therefore, the linkage between the genes of the two MHC classes appears to be primitive and to have a long evolutionary history.