Sammendrag
The Atlantic cod (Gadus morhua) is a commercially important fish in Norway and a better understanding of its immune system is a pre-requisite to devise better disease management strategies that are essential for successful farming of this species. In common with other teleosts, the Atlantic cod is thought to rely heavily on its innate immune system for protection against microbial exploitation. In this context, antimicrobial peptides are particularly important, since they play a crucial role as the first line of host defence against invading microorganisms. Using an in silico approach we have identified a piscidin gene in Atlantic cod, the first to be reported from a basal teleost (Paracanthopterygii). This gene consists of two introns and three exons. It was found to be under positive selection, indicating that it may play a role in adaptation to new environments or evolving pathogens. The predicted mature cod piscidin contains 22 residues, including four conserved histidines and its sequence shows very high similarity with piscidins from other fish species. Expression studies showed that cod piscidin is expressed in several mucosal 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 show that piscidins are ancient defence factors and that cod piscidin may be involved in its innate immune response against invading pathogens.
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