Sequence and expression analysis of an interferon stimulated gene (ISG15) from Atlantic cod (Gadus morhua L.).

Suppression subtractive hybridization was used to examine gene expression in Atlantic cod head kidney cells treated with polyinosinic polycytidylic acid (poly I:C). One of the most abundant genes was ISG15, showing 24-53% amino acid similarity to ISG15 from both mammals and teleosts. The promoter was cloned by genome walking and three potential interferon-stimulated response elements (ISREs) were identified. Analysis of the gene structure revealed a single intron in the 5' untranslated region (UTR) of cod ISG15, which also seems to be present in zebrafish and pufferfish ISG15. A quantitative real time PCR assay was established to monitor the gene expression of cod ISG15. Injection of cod with poly I:C strongly induced the expression of ISG15 in all organs investigated. Stimulation was most pronounced the first day with a gradual decline the following days. The expression of ISG15 in head kidney cells was also induced in vitro by treatment with poly I:C, but not significantly with LPS. However, injection of formalin killed Vibrio anguillarum-induced ISG15 expression in head kidney.