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Fast evolution of interleukin-2 in mammals and positive selection in ruminants.
Journal of Molecular Evolution
Interleukin-2 (IL-2) is a cytokine involved in induction and regulation of the immune response in mammals. There have been numerous reports about the search for IL-2 in species other than mammals, and recently an IL-2-like gene has been isolated in chicken. Using PCR, we searched for IL-2 gene sequences in a wide variety of mammals, including marsupials and monotremes, as well as in birds. Although we can readily amplify IL-2 gene fragments in placental mammals, no amplification was obtained in other species. This is best explained by very high substitution rates. This suggest that strategies to isolate IL-2 homologous genes outside mammals should involve functional assays, as for the chicken gene, and not hybridization-based techniques. Nonsynonymous substitution rates are especially high in ruminants, due to positive selection acting on regions important in term of structure-function. We suggest that, although globally similar, the immune response of various mammals is not identical, mainly at the level of cytokine-mediated regulations.
Amino Acid Sequence, Amino Acid Substitution, Animals, Cytokines/genetics, Evolution, Molecular, Humans, Interleukin-2/genetics, Mammals/genetics, Mammals/immunology, Molecular Sequence Data, Phylogeny, Polymerase Chain Reaction, Ruminants/genetics, Ruminants/immunology, Selection, Genetic, Sequence Homology, Amino Acid
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