Characterization and expression analysis of type I interferon in common carp Cyprinus carpio L

The type I interferon (I-IFN) gene has recently been cloned and sequenced in the common carp species Cyprinus carpio L. Carp I-IFN cDNA is composed of 675 base pairs and is translated into a protein of 186 amino acid residues. The carp I-IFN encodes a predicted signal peptide of 23 amino acid residues and contains the I-IFN family signature His(140)-Trp(158). Analysis of the homology between carp I-IFN and other known I-IFN and type II interferon (II-IFN) family members has revealed significant similarities to grass carp I-IFN. Phylogenetic analysis demonstrated that carp I-IFN clusters with I-IFN in teleosts, away from the other II-IFN family members. In addition, the gene structure for carp I-IFN is composed of 5 exons and 4 introns, a composition that is similar to that of the teleost I-IFN gene. RT-PCR analysis did not reveal gene expression in un-stimulated tissues including intestine, liver, gill, head kidney, muscle, spleen, mid-kidney and skin. However, I-IFN expression levels increased following stimulation with imiquimod in the head kidney cells. Furthermore, recombinant carp I-IFN protein (mature form) produced via the cell-free protein synthesis system stimulated the expression of the interferon-inducible Mx gene in the head kidney cells.