Fast evolution of interleukin-2 in mammals and positive selection in ruminants.
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.
Zelus
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D
UMR 5665 du CNRS, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364 Lyon Cedex 07, France.
Robinson-Rechavi
M
M
Delacre
M
M
Auriault
C
C
Laudet
V
V
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D016207:Cytokines / Q000235:genetics; D019143:Evolution, Molecular; D006801:Humans; D007376:Interleukin-2 / Q000235:genetics*; D008322:Mammals / Q000235:genetics / Q000276:immunology; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012418:Ruminants / Q000235:genetics* / Q000276:immunology*; D012641:Selection, Genetic; D017386:Sequence Homology, Amino Acid
D016207:Cytokines; D007376:Interleukin-2