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，它将外来抗原呈递给效应T细胞并启动脊椎动物的免疫系统。在哺乳动物和鸟类中对MHC基因进行了广泛的研究，已知它们具有高遗传多态性的多基因位点。为了了解脊椎动物MHC基因的进化，我们分析了一种硬骨鱼，Medaka鱼（Oryzias latipes）的基因，它是低等脊椎动物中唯一一种具有许多近交系的物种。本项目采用PCR方法分离出三种medaka鱼MHC II类B基因，并与哺乳动物、鸟类、慈鱼和斑马鱼的同源基因进行比较。MHCⅱ类B的分子系统发育树表明，从斑马鱼和鲷鱼的共同祖先MHC基因分离后，在鳉鱼分支中分离出三种类型的MHC基因。为了在medaka鱼中构建转基因系统，我们分离并鉴定了一个酪氨酸酶基因作为标记。在此过程中，我们发现了medaka鱼白化突变体基因中的一个转座因子。

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.