Identification, expression, and innate immune responses of two insulin-like peptide genes in the razor clam Sinonovacula constricta

• Two insulin-like peptide (ILP) genes were characterized from the razor clam Sinonovacula constricta.
• The ILP transcripts were widely expressed in adult tissues and the early developmental stages.
• The expression of the two ILP genes was significantly up-regulated after infection.

Insulin-like peptide (ILP) has emerged as a cell regulatory factor with multiple functions in vertebrates and invertebrates. In the present study, we identified and characterized two ILP genes, ILP1 and ILP2, in the razor clam Sinonovacula constricta. Both ILPs have a signal peptide and a mature domain consisting of six strictly conserved cysteines. The tertiary structure is divided into three main α-helices with a C-domain loop that separates helix 1 from helix 2. Both of ILPs were found to be regulated according to tissue type and developmental stage. After challenge with Vibrio anguillarum, Vibrio parahaemolyticus and Micrococcus lysodeikticus, the expression of two ILP genes was significantly up-regulated in the liver, hemocytes and mantle tissues, suggesting that the ILPs may play roles in the innate immunity in the razor clam Sinonovacula constricta.