Dicer (Dcr) is the key protein of the RNA interference (RNAi) pathway. To investigate the role of the RNAi pathway in shrimp anti-viral immunity, Litopenaeus vannamei Dcr2 (designated as LvDcr2) was identified and characterized. The full-length cDNA of LvDcr2 was 5513bp long, with an open reading frame encoding a putative protein of 1502 amino acids. In addition, five proteins homologous to the single von Willebrand factor type C (VWC) domain protein (SVC) were also identified in L. vannamei and named LvSVC1-5. These LvSVCs were between 102 and 190 amino acids in length and all contained a motif similar to Drosophila melanogaster SVC proteins (DmSVCs). By co-immunoprecipitation assays and pull-down assays, we demonstrated that LvDcr2, L. vannamei Argonaute 2 (LvAgo2), and L. vannamei transactivating response RNA-binding protein isoform 1 (LvTRBP1) interacted with each other. A luciferase reporter assay indicated that the promoters of LvSVC1, LvSVC4, LvSVC5, and DmSVC Vago (DmVago) were activated by LvDcr2 as well as by Drosophila Dcr2 (DmDcr2). Real-time RT-PCR showed that LvDcr2 and LvSVCs were up-regulated in immune responses against Poly(C-G) or WSSV challenge. These results suggested that LvDcr2 formed complexes with LvAgo2 and LvTRBP1 to act as the cores of shrimp small interfering RNA (siRNA)-induced silencing complex (siRISC)/siRISC-loading complex (siRLC), role in shrimp siRNA pathway. Furthermore, these results also suggested that LvDcr2 may engage in non-specific activation of anti-viral immunity.
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