Ornithorhynchus anatinus (platypus) links the evolution of immunoglobulin genes in eutherian mammals and nonmammalian tetrapods.
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.
Zhao
Yaofeng
Y
State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, People's Republic of China. yaofengzhao@cau.edu.cn
Cui
Huiting
H
Whittington
Camilla M
CM
Wei
Zhiguo
Z
Zhang
Xiaofeng
X
Zhang
Ziding
Z
Yu
Li
L
Ren
Liming
L
Hu
Xiaoxiang
X
Zhang
Yaping
Y
Hellman
Lars
L
Belov
Katherine
K
Li
Ning
N
Hammarström
Lennart
L
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*
C008104:IgO; D007127:Immunoglobulin Constant Regions; D007072:Immunoglobulin D; D007143:Immunoglobulin Heavy Chains; D007132:Immunoglobulin Isotypes; D007138:Immunoglobulin delta-Chains; D007136:Immunoglobulins