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

主要组织相容性复合体(MHC)是一种细胞表面糖蛋白，呈递外源抗原给效应T细胞，启动脊椎动物的免疫系统。MHC基因在哺乳动物和鸟类中得到了广泛的研究，并已被认为具有多个基因位点，具有高度的遗传多态。为了了解脊椎动物MHC基因的进化，我们分析了唯一在低等脊椎动物中拥有大量近交系的硬骨鱼Medaka鱼的基因。在本项目中，我们通过聚合酶链式反应分离了三种类型的Medaka鱼MHC II类B基因，并将这些序列与哺乳动物、鸟类、慈嘴鱼和斑马鱼的同源基因进行了比较。MHCⅡB类的分子系统树分析表明，从斑马鱼和斑马鱼MHC基因的共同祖先中分离到青花鱼分支中的3种MHC基因。为了构建青花鱼MHC基因的转基因系统，我们分离并鉴定了一个酪氨酸酶基因。在这个过程中，我们可以在青冈鱼的白化突变体的基因中发现一个转座子。

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.