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Multiple IgH Isotypes Including IgD, Subclasses of IgM, and IgY Are Expressed in the Common Ancestors of Modern Birds.

Posted by on in 2016
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Han B1Yuan H2Wang T1Li B3Ma L1Yu S1Huang T4Li Y5Fang D3Chen X3Wang Y3Qiu S3Guo Y1Fei J1Ren L1Pan-Hammarström Q6Hammarström L6Wang J3Wang J3Hou Y3Pan Q7Xu X8Zhao Y92016. J Immunol. 196(12):5138-47. doi: 10.4049/jimmunol.1600307. Epub 2016 May 16.

1State Key Laboratory for Agrobiotechnology, China Agricultural University, Beijing 100193, People's Republic of China;
2BGI-Shenzhen, Shenzhen 518083, People's Republic of China; College of Animal Science and Technology, Northeast Agricultural University, Harbin 150030, People's Republic of China;
3BGI-Shenzhen, Shenzhen 518083, People's Republic of China;
4School of Life Science, Henan University, Kaifeng 475004, People's Republic of China;
5Key Laboratory of Animal Reproduction and Germplasm Enhancement in Universities of Shandong, Qingdao Agricultural University, Qingdao 266109, People's Republic of China; and.
6Division of Clinical Immunology, Department of Laboratory Medicine, Karolinska University Hospital Huddinge, SE-141 86, Stockholm, Sweden.
7Key Laboratory of Animal Reproduction and Germplasm Enhancement in Universities of Shandong, Qingdao Agricultural University, Qingdao 266109, People's Republic of China; and yaofengzhao@cau.edu.cn xuxun@genomics.cn qjpan@126.com.
8BGI-Shenzhen, Shenzhen 518083, People's Republic of China; yaofengzhao@cau.edu.cn xuxun@genomics.cn qjpan@126.com.
9State Key Laboratory for Agrobiotechnology, China Agricultural University, Beijing 100193, People's Republic of China; yaofengzhao@cau.edu.cn xuxun@genomics.cn qjpan@126.com.

Abstract

Although evolutionarily just as ancient as IgM, it has been thought for many years that IgD is not present in birds. Based on the recently sequenced genomes of 48 bird species as well as high-throughput transcriptome sequencing of immune-related tissues, we demonstrate in this work that the ostrich (Struthio camelus) possesses a functional δ gene that encodes a membrane-bound IgD H chain with seven CH domains. Furthermore, δ sequences were clearly identified in many other bird species, demonstrating that the δ gene is widely distributed among birds and is only absent in certain bird species. We also show that the ostrich possesses two μ genes (μ1, μ2) and two υ genes (υ1, υ2), in addition to the δ and α genes. Phylogenetic analyses suggest that subclass diversification of both the μ and υ genes occurred during the early stages of bird evolution, after their divergence from nonavian reptiles. Although the positions of the two υ genes are unknown, physical mapping showed that the remaining genes are organized in the order μ1-δ-α-μ2, with the α gene being inverted relative to the others. Together with previous studies, our data suggest that birds and nonavian reptile species most likely shared a common ancestral IgH gene locus containing a δ gene and an inverted α gene. The δ gene was then evolutionarily lost in selected birds, whereas the α gene lost in selected nonavian reptiles. The data obtained in this study provide significant insights into the understanding of IgH gene evolution in tetrapods.

PMID:
 
27183632
 
DOI:
 
10.4049/jimmunol.1600307
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