Molecular Cloning and Phylogenetic Analysis of the Atlantic Salmon Immunoglobulin D Gene

• Published in: Scandinavian Journal of Immunology
• Main Authors: Hordvik, Thevarajan, Samdal, Bastani, Krossøy
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1999
• Subjects: Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1046/j.1365-3083.1999.00583.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1046%2Fj.1365-3083.1999.00583.x; https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3083.1999.00583.x

A gene homologous to the IgD heavy chain (δ) gene in channel catfish ( Ictalurus punctatus ) was found 0.9 kb downstream of the IgM heavy chain (μ) gene in Atlantic salmon ( Salmo salar ). As in catfish, the first constant μ exon is spliced into the δ transcripts. In agreement with the tetraploid ancestry of the salmonid fish family there are two highly similar δ genes in Atlantic salmon. Characterization of these genes showed that they encode seven ‘unique’ Ig domains, three of which are tandem duplicated, i.e. like δ1–(δ2–δ3–δ4)*–(δ2–δ3–δ4)–δ5–δ6–δ7. Sequence analysis indicates that δ1–δ7 arose from two duplication events. Accordingly, salmon δ can be reduced to a unit of three Ig domains corresponding to the three C‐terminal domains of a prototypic Ig molecule. The ancestral three‐domain unit is apparently best conserved in δ1–δ5–δ6. Phylograms indicate a relationship between teleost and mammalian IgD mainly because of the similarity between the teleost δ5 and human δ2. The corresponding domain in mouse IgD has been deleted during evolution. The teleost δ1 and δ6 sequences are most similar to domains of other non‐IgM isotypes, including those in cartilaginous fishes.