Molecular cloning, characterization, and expression analysis of a disease-resistance related CC chemokine gene in miiuy croaker (Miichthys miiuy)

Chemokines control leukocyte trafficking which plays important roles in resistance to pathogenic infection. Here, a full-length CC chemokine (MimiCC2) cDNA was isolated from miiuy croaker (Miichthys miiuy) by EST analysis and RACE-PCR. Its open reading frame is 300 nucleotides, encoding a polypeptide of 99 amino acids. The deduced MimiCC2 contains a 23-aa signal peptide and a 76-aa matural peptide, which possesses the four invariant cysteine residues as found in other known CC chemokines. It shares 13.3% to 73.7% sequence identities to mammalian and fish CC chemokines, with the highest identity observed between MimiCC2 and seabream CCL4. Homology modeling showed that MimiCC2 had a tertiary structure containing three β-strands and an α-helix. Three exons and two introns were identified in miiuy croaker CC. Phylogenetic analysis showed that miiuy croaker CC is similar to CCL4. In normal miiuy croaker, MimiCC2 was expressed in all the tissues examined. Infection of miiuy croaker with Vibrio anguillarum significantly increased expression of MimiCC2 in the immune-related organs. These results indicated that MimiCC2 probably plays important role in miiuy croaker immune system.