Cloning and expression analysis of the Dscam gene during the inducing immune priming (Quasi-immune) response in Fenneropenaeus chinensis

To explore the function of Dscam gene of Chinese shrimp Fenneropenaeus chinensis (FcDscam) during the immune priming response, we cloned the cDNA sequence using the rapid amplification of cDNA ends (RACE), and then analyzed the features of this gene based on bioinformatics software. The full length of FcDscam cDNA is 6624 bp, with a 5′-untranslated region (UTR) of 171 bp, a 3′-untranslated region (UTR) of 459 bp, and an opening reading frame (ORF) of 5 994 bp, and it encoded 1 996 amino acids. The protein encoded by FcDscam contains 1 signal peptide, 1 cytoplasmic tail, 1 transmembrane domain, 6 of fibronectin type Ⅲ (FNⅢ) and 10 of immunoglobulin(Ig). As shown by the homology search and neighbor-joining phylogenetic tree, FcDscam gene had the highest homology with that of Litopenaeus vannamei (92.4%). To induce the immune response, test animals were first fed with heat-inactivated WSSV bait for six days and infected again 12 days later. Samples were collected at 0, 6 and 12 d of the first-time infection and 12, 24, 48, 72 and 168 h of the second-time infection, respectively, for analysing the mRNA expression level of FcDscam by real-time PCR. On the 12th day of the first infection, its expression level in induced infection group began to increase, significantly different from those in the negative control group and the non-induced infection group. After 24 h of the second-time infection, its expression level in the infection group reached a maximum, significantly different from those of the negative control group and the non-induced infection group, and the expression level started to decline at the 48 h. Our research demonstrated the existence of the Dscam gene in F. chinensis, and its important role in the process of immune sensitization.