Molecular characterization and expression of twenty interleukin-17 transcripts in the common Chinese cuttlefish (Sepiella japonica) in response to Vibrio harveyi infection.

The common Chinese cuttlefish (Sepiella japonica) is an essential species for stock enhancement by releasing juveniles in the East China Sea now. S. japonica is susceptible to bacterial diseases during parental breeding. In vertebrates, Interleukin-17 (IL-17) cytokine family plays critical roles in both acute and chronic inflammatory responses. In Cephalopoda, few studies have been reported on IL-17 genes so far. In this study, twenty IL-17 transcripts obtained from S. japonica were divided into eight groups (designated as Sj_IL-17-1 to Sj_IL-17-8). Multiple alignment analysis showed that IL-17s in S. japonica and human both contained four β-folds (β1-β4), except for Sj_IL-17-6 with two β-folds (β1 and β2), and the third and fourth β-folds of Sj_IL-17-5 and Sj_IL-17-8 were longer than those of other Sj_IL-17. Protein structure and conserved motifs analysis demonstrated that Sj_IL-17-5 and Sj_IL-17-6 displayed different protein structure with respect to other six Sj_IL-17 proteins. The homology and phylogenetic analysis of amino acids showed that Sj_IL-17-5, Sj_IL-17-6 and Sj_IL-17-8 had low homology with the other five Sj_IL-17s. Eight Sj_IL-17 mRNAs were ubiquitously expressed in ten examined tissues, with dominant expression in the hemolymph. qRT-PCR data showed that the mRNA expression levels of Sj_IL-17-2, Sj_IL-17-3, Sj_IL-17-6, and Sj_IL-17-8 were significantly up-regulated in infected cuttlefishes, and Sj_IL-17-2, Sj_IL-17-6, Sj_IL-17-7, and Sj_IL-17-8 mRNAs Awere significantly up-regulated after bath infection of Vibrio harveyi, suggesting that certain Sj_IL-17s were involved in the immune response of S. japonica against V. harveyi infection. These results implied that Sj_IL-17s were likely to have distinct functional diversification. This study aims to understand the involvement of Sj_IL-17 genes in immune responses of cuttlefish against bacterial infections.