title: Ornithorhynchus anatinus (platypus) links the evolution of immunoglobulin genes in eutherian mammals and nonmammalian tetrapods.
abstract: 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.
authors.affiliation: State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, People's Republic of China. yaofengzhao@cau.edu.cn
authors.forename: Yaofeng
authors.initials: Y
authors.lastname: Zhao
authors.forename: Huiting
authors.initials: H
authors.lastname: Cui
authors.forename: Camilla M
authors.initials: CM
authors.lastname: Whittington
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Wei
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Zhang
authors.forename: Ziding
authors.initials: Z
authors.lastname: Zhang
authors.forename: Li
authors.initials: L
authors.lastname: Yu
authors.forename: Liming
authors.initials: L
authors.lastname: Ren
authors.forename: Xiaoxiang
authors.initials: X
authors.lastname: Hu
authors.forename: Yaping
authors.initials: Y
authors.lastname: Zhang
authors.forename: Lars
authors.initials: L
authors.lastname: Hellman
authors.forename: Katherine
authors.initials: K
authors.lastname: Belov
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.forename: Lennart
authors.initials: L
authors.lastname: Hammarström
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019143:Evolution, Molecular; D005260:Female; D006801:Humans; D007127:Immunoglobulin Constant Regions / Q000235:genetics; D007072:Immunoglobulin D / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D007132:Immunoglobulin Isotypes / Q000235:genetics*; D007138:Immunoglobulin delta-Chains / Q000235:genetics; D007136:Immunoglobulins / Q000235:genetics*; D008297:Male; D008322:Mammals / Q000235:genetics* / Q000276:immunology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010987:Platypus / Q000235:genetics* / Q000276:immunology*
chemical_list: C008104:IgO; D007127:Immunoglobulin Constant Regions; D007072:Immunoglobulin D; D007143:Immunoglobulin Heavy Chains; D007132:Immunoglobulin Isotypes; D007138:Immunoglobulin delta-Chains; D007136:Immunoglobulins