Modes of Salmonid MHC Class I and II Evolution Differ from the Primate Paradigm

• Published in: The Journal of immunology (1950) Vol. 166; no. 5; pp. 3297 - 3308
• Main Authors: Shum, Benny P, Guethlein, Lisbeth, Flodin, Laura R, Adkison, Mark A, Hedrick, Ronald P, Nehring, R. Barry, Stet, Rene J. M, Secombes, Christopher, Parham, Peter
• Format: Journal Article
• Language: English
• Published: United States Am Assoc Immnol 01-03-2001
• Subjects: Alleles; Amino Acid Sequence; Animals; Antigen Presentation - genetics; Celbiologie en Immunologie; Cell Biology and Immunology; DAB gene; Evolution, Molecular; Female; Genes, MHC Class I; Genes, MHC Class II; Genetic Variation - immunology; Humans; Introns - immunology; Leerstoelgroep Celbiologie en immunologie; Molecular Sequence Data; Oncorhynchus - genetics; Oncorhynchus - immunology; Oncorhynchus mykiss; Oncorhynchus mykiss - genetics; Oncorhynchus mykiss - immunology; Phylogeny; Primates; Recombination, Genetic - immunology; Salmo trutta; Sequence Homology, Amino Acid; UBA gene; WIAS
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.166.5.3297

Rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) represent two salmonid genera separated for 15--20 million years. cDNA sequences were determined for the classical MHC class I heavy chain gene UBA and the MHC class II beta-chain gene DAB from 15 rainbow and 10 brown trout. Both genes are highly polymorphic in both species and diploid in expression. The MHC class I alleles comprise several highly divergent lineages that are represented in both species and predate genera separation. The class II alleles are less divergent, highly species specific, and probably arose after genera separation. The striking difference in salmonid MHC class I and class II evolution contrasts with the situation in primates, where lineages of class II alleles have been sustained over longer periods of time relative to class I lineages. The difference may arise because salmonid MHC class I and II genes are not linked, whereas in mammals they are closely linked. A prevalent mechanism for evolving new MHC class I alleles in salmonids is recombination in intron II that shuffles alpha 1 and alpha 2 domains into different combinations.