Cloning, characterization and expression analysis of a CXCL10-like chemokine from turbot (Scophthalmus maximus)

Chemokines represent a superfamily of chemotactic cytokines playing an important role in leukocyte chemotaxis. We have constructed a turbot spleen cDNA library that has over 2.2 × 106 primary clones. Its average insert size was estimated to about 700-2000 bp by PCR of 40 randomly picked clones. A novel turbot CXC chemokine was screened from this library. Both 5′-RACE and 3′-RACE were carried out in order to obtain the complete cDNA, which contains a 79 bp 5′ UTR, a 372 bp open reading frame encoding 123 amino acids and a 227 bp 3′ UTR. Four exons and three introns were identified in the turbot CXC chemokine gene. The three introns were 591 bp, 86 bp and 125 bp, respectively. Both BLASTP similarity comparisons and Phylogenetic analysis showed that the turbot CXC chemokine was closer to CXCL10. Interestingly, the highest expression levels of the turbot CXC chemokine were detected at 12 h in liver and spleen after challenge with V. anguillarum and at 5 h in head kidney. The expression in liver decreased gradually after 12 h and returned the level of background after 72 h. In spleen, the expression kept high levels till 24 h and then became faint consistent with background. The expression of the CXC chemokine was not detected in normal tissues of turbot, which suggested it only was induced when challenged with V. anguillarum. These results indicated that the turbot CXC chemokine played an important role in turbot immune response.