TRANSGENIC ANALYSIS OF MAJOR HISTOCOMPATIBILITY COMPLEX IN MEDAKA FISH : ITS MOLECULAR EVOLUTION AND GENETIC POLYMORPHISM

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Major histocompatibility complex (MHC) is the cell surface glycoprotein which presents foreign antigens to effector T cells and initiates the immune system of vertebrates. MHC genes have been studied extensively in mammals and birds, and it has been known that they have multi gene loci with high genetic polymorphism. In order to understand the evolution of MHC genes in vertebrates, we analyzed the genes of a teleost, Medaka fish (Oryzias latipes), which is the only one species having many inbred strains in lower vertebrates.In this project, we could isolate three types of medaka fish MHC class II B genes by PCR procedure, and compared these sequences together with homologous genes from mammals, birds, cichlid fish and zebrafish. Molecular phylogenetic tree of MHC class II B indicated that three types of MHC genes in medaka fish were separated in the medaka fish branch after separation from common ancestor of zebrafish and cichlid fish MHC genes.To construct a transgenic system in medaka fish, we isolated and characterized a tyrosinase gene as a marker. In this process, we could find a transposable element in the gene of albino mutant of medaka fish.