Evolution of duplicated IgH loci in Atlantic salmon, Salmo salar.
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.
Yasuike
Motoshige
M
Department of Biology, University of Victoria,Victoria, British Columbia, Canada.
de Boer
Johan
J
von Schalburg
Kristian R
KR
Cooper
Glenn A
GA
McKinnel
Linda
L
Messmer
Amber
A
So
Stacy
S
Davidson
William S
WS
Koop
Ben F
BF
D000818:Animals; D001267:Atlantic Ocean; D019143:Evolution, Molecular; D020440:Gene Duplication / Q000235:genetics*; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D015326:Gene Rearrangement, B-Lymphocyte, Heavy Chain / Q000235:genetics; D050438:Genes, Immunoglobulin Heavy Chain / Q000235:genetics*; D056426:Genetic Loci / Q000235:genetics*; D014644:Genetic Variation; D007127:Immunoglobulin Constant Regions / Q000737:chemistry / Q000235:genetics; D007135:Immunoglobulin Variable Region / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020317:Salmo salar / Q000235:genetics*; D016415:Sequence Alignment
D007127:Immunoglobulin Constant Regions; D007135:Immunoglobulin Variable Region
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