Sammendrag
Atlantic cod (Gadus morhua) is a commercially important fish species. A better understanding of the immune system of Atlantic cod is a pre-requisite to devise better disease management strategies. The adaptive immune system of this fish is rather different from other teleosts and the role of antibodies in protective immunity is still a matter of debate. The innate immune components including the antimicrobial peptides may be key effectors in host defence against invading pathogens. The piscidin family of antimicrobial peptides comprises potent peptides of 22-44 amino acid residues that have broad-spectrum activity against bacteria, virus, fungi and parasites. They were first isolated from the mast cells of hybrid striped bass but recent reports have shown that piscidins are found in various species of Acanthopterygii. In this study, we have identified a gene encoding for the piscidin prepropeptide in Atlantic cod. This gene consists of two introns and three exons (Fig 1). The predicted mature peptide contains 22 residues, including the four conserved histidines, and its sequence shows similarity with other reported piscidins and piscidin-like peptides from fish. Expression studies showed that cod piscidin is expressed in several tissues of clinically normal fish as well as in early developmental stages. In addition, expression changes at the mRNA level were observed after challenge with heat killed bacteria. Importantly, our results demonstrate for the first time that piscidins are ancient defence factors that are more widespread amongst teleosts than hitherto thought and that they may have other functions in addition to their role in innate immunity.
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