Elucidation of the molecular evolution of MHC family and the establishment of the acquired immune system

具有特征性结构的MHC家族具有多种重要的生物学功能，包括经典MHC分子向T细胞的肽呈递。然而，MHC家族的分子进化尚不清楚。为了进一步了解MHC家族的起源和多样性以及获得性免疫系统的建立，我们对软骨鱼类等原始动物的MHC样分子进行了研究。根据氨基酸序列和结构特征，MHC家族可分为I类和II类。先前，我们证明MHC家族分子存在于最原始的有颌脊椎动物，软骨鱼中，并且这两个类已经在鱼类水平上建立起来了。此外，我们还报道了产生典型MHC分子异常高多态性的机制的普遍性，这是同种异体移植排斥反应的基础。关于这两个类的建立，我们最近澄清了一个具有这两个类特征的新基因，并揭示了它属于一个非常独特的连锁群。在本研究中，我们还从基因组中MHC区域的进化角度分析了MHC相关基因。

The MHC family with the characteristic structure has various important biological functions including the peptide-presentation to T cells by the classical MHC molecules. However, the molecular evolution of the MHC family has not been clarified yet. To further understand the origin and the diversity of the MHC family and the establishment of the acquired immune system, we have been investigating the MHC-like molecules from primitive animals such as the cartilaginous fish. The MHC family can be classified into two classes, the class I and the class II, based on amino acid sequences and structural characteristics. Previously, we demonstrated that the MHC family molecules exist in the most primitive jawed vertebrates, the cartilaginous fish, and that the two classes has already been established at the level of fish. Further, we reported the generality of the mechanisms that create exceptionally high polymorphism of the classical MHC molecules, which is the basis of the allograft rejection. In relation to the establishment of the two classes, we recently clarified a novel gene that possesses the characteristics of both classes, and revealed that it belongs to a very unique linkage group. In this study, we also analyzed the MHC-related genes from the standpoint of the evolution of the MHC region in the genome.