Zhao Yaofeng, Cui Huiting, Whittington Camilla M, Wei Zhiguo, Zhang Xiaofeng, Zhang Ziding, Yu Li, Ren Liming, Hu Xiaoxiang, Zhang Yaping, Hellman Lars, Belov Katherine, Li Ning, Hammarström Lennart
State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, People's Republic of China.
J Immunol. 2009 Sep 1;183(5):3285-93. doi: 10.4049/jimmunol.0900469. Epub 2009 Aug 12.
The evolutionary origins of mammalian immunoglobulin H chain isotypes (IgM, IgD, IgG, IgE, and IgA) are still incompletely understood as these isotypes differ considerably in structure and number from their counterparts in nonmammalian tetrapods. We report in this study that the platypus (Ornithorhynchus anatinus) Ig H chain constant region gene locus contains eight Ig encoding genes, which are arranged in an mu-delta-omicron-gamma2-gamma1-alpha1-epsilon-alpha2 order, spanning a total of approximately 200 kb DNA, encoding six distinct isotypes. The omicron (omicron for Ornithorhynchus) gene encodes a novel Ig H chain isotype that consists of four constant region domains and a hinge, and is structurally different from any of the five known mammalian Ig classes. This gene is phylogenetically related to upsilon (epsilon) and gamma, and thus appears to be a structural intermediate between these two genes. The platypus delta gene encodes ten heavy chain constant region domains, lacks a hinge region and is similar to IgD in amphibians and fish, but strikingly different from that in eutherian mammals. The platypus Ig H chain isotype repertoire thus shows a unique combination of genes that share similarity both to those of nonmammalian tetrapods and eutherian animals and demonstrates how phylogenetically informative species can be used to reconstruct the evolutionary history of functionally important genes.
哺乳动物免疫球蛋白重链同种型（IgM、IgD、IgG、IgE和IgA）的进化起源仍未完全明了，因为这些同种型在结构和数量上与其非哺乳动物四足动物的对应物有很大差异。我们在本研究中报告，鸭嘴兽（Ornithorhynchus anatinus）的Ig重链恒定区基因座包含八个Ig编码基因，它们按μ-δ-ο-γ2-γ1-α1-ε-α2的顺序排列，跨越总共约200 kb的DNA，编码六种不同的同种型。ο（鸭嘴兽的ο）基因编码一种新型的Ig重链同种型，它由四个恒定区结构域和一个铰链区组成，在结构上与已知的五种哺乳动物Ig类别中的任何一种都不同。该基因在系统发育上与υ（ε）和γ相关，因此似乎是这两个基因之间的结构中间体。鸭嘴兽的δ基因编码十个重链恒定区结构域，缺乏铰链区，与两栖动物和鱼类的IgD相似，但与真兽类哺乳动物的IgD明显不同。鸭嘴兽的Ig重链同种型库因此显示出一组独特的基因组合，这些基因既与非哺乳动物四足动物的基因相似，也与真兽类动物的基因相似，并展示了如何利用具有系统发育信息的物种来重建功能重要基因的进化历史。
