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* State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing, Peoples Republic of China;
Medical University of South Carolina, Marine Biomedicine and Environmental Sciences Center, Charleston, SC 29425; and
Division of Clinical Immunology, Department of Laboratory Medicine, Karolinska University Hospital Huddinge, Stockholm, Sweden
The reptiles are the last major group of jawed vertebrates in which the organization of the IGH locus and its encoded Ig H chain isotypes have not been well characterized. In this study, we show that the green anole lizard (Anolis carolinensis) expresses three Ig H chain isotypes (IgM, IgD, and IgY) but no IgA. The presence of the 
gene in the lizard demonstrates an evolutionary continuity of IgD from fishes to mammals. Although the germline gene contains 11 CH exons, only the first 4 are used in the expressed IgD membrane-bound form. The µ chain lacks the cysteine in CH1 that forms a disulfide bond between H and L chains, suggesting that (as in IgM of some amphibians) the H and L polypeptide chains are not covalently associated. Although conventional IgM transcripts (four CH domains) encoding both secreted and membrane-bound forms were detected, alternatively spliced transcripts encoding a short membrane-bound form were also observed and shown to lack the first two CH domains (VDJ-CH3-CH4-transmembrane region). Similar to duck IgY, lizard IgY H chain (
) transcripts encoding both full-length and truncated (IgY
Fc) forms (with two CH domains) were observed. The absence of an IgA-encoding gene in the lizard IGH locus suggests a complex evolutionary history for IgA in the saurian lineage leading to modern birds, lizards, and their relatives.
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1 This work was supported by National Science Fund for Distinguished Young Scholars Grant 30725029, Program for New Century Excellent Talents in University of China, National Key Basic Research Program Grant 2006CB102100, and National Natural Science Foundation of China Grant 30671497.
This material is based in part on work supported by the National Science Foundation. Any opinion, finding, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.
2 Z.W. and Q.W. contributed equally to this work.
3 Current address: Division of Molecular and Cellular Biosciences, National Science Foundation, 4201 Wilson Boulevard, Arlington, VA 22230.
4 Address correspondence and reprint requests to Dr. Yaofeng Zhao, State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, Peoples Republic of China. E-mail address: yaofengzhao{at}cau.edu.cn, or Dr. Ning Li, State Key Laboratory of Agrobiotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, Peoples Republic of China. E-mail address: ninglcau{at}cau.edu.cn
5 Abbreviations used in this paper: IGH, Ig H chain gene; IGL, Ig L chain gene; BLAST, basic local alignment search tool; NCBI, National Center for Biotechnology Information; IgSF, Ig superfamily; TM, transmembrane region; sIg, secretory Ig.
6 The online version of this article contains supplemental material.
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