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Open Access Highly Accessed Research article

Evolution of duplicated IgH loci in Atlantic salmon, Salmo salar

Motoshige Yasuike1, Johan de Boer1, Kristian R von Schalburg1, Glenn A Cooper1, Linda McKinnel1, Amber Messmer1, Stacy So1, William S Davidson2 and Ben F Koop1*

  • * Corresponding author: Ben F Koop bkoop@uvic.ca

  • † Equal contributors

Author Affiliations

1 Department of Biology, University of Victoria, PO Box 3020 STN CSC, Victoria, British Columbia, V8W 3N5, Canada

2 Department of Molecular Biology and Biochemistry, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, V5A1S6, Canada

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BMC Genomics 2010, 11:486  doi:10.1186/1471-2164-11-486

Published: 2 September 2010

Abstract

Background

The Atlantic salmon (Salmo salar) immunoglobulin heavy chain (IgH) locus possesses two parallel IgH isoloci (IGH-A and IGH-B), that are related to the genomic duplication event in the family Salmonidae. These duplicated IgH loci in Atlantic salmon provide a unique opportunity to examine the mechanisms of genome diversity and genome evolution of the IgH loci in vertebrates. In this study, we defined the structure of these loci in Atlantic salmon, and sequenced 24 bacterial artificial chromosome (BAC) clones that were assembled into the IGH-A (1.1 Mb) and IGH-B (0.9 Mb) loci. In addition, over 7,000 cDNA clones from the IgH variable (VH) region have been sequenced and analyzed.

Results

The present study shows that the genomic organization of the duplicated IgH loci in Atlantic salmon differs from that in other teleosts and other vertebrates. The loci possess multiple Cτ genes upstream of the Cμ region, with three of the Cτ genes being functional. Moreover, the duplicated loci possess over 300 VH segments which could be classified into 18 families. This is the largest number of VH families currently defined in any vertebrate. There were significant structural differences between the two loci, indicating that both IGH-A and -B loci have evolved independently in the short time after the recent genome duplication approximately 60 mya.

Conclusions

Our results indicate that the duplication of the IgH loci in Atlantic salmon significantly contributes to the increased diversity of the antibody repertoire, as compared with the single IgH locus in other vertebrates.