Cloning, characterization, and biological function analysis of the SidT2 gene from Siniperca chuatsi

The systemic RNA interference defective protein (SID)-1 plays an important role in dsRNA uptake in cells. We identified the ScSidT2 gene from the mandarin fish (Siniperca chuatsi), which is the first-studied SID-1 homolog in fish. ScSidT2 mRNA is 3380 bp long and contains a 2568-bp open reading frame that encodes an 855-amino-acid protein with an N-terminal signal peptide and ten putative transmembrane domains. Tissue distribution profile in healthy fish and expression profiles of ScSidT2 in infectious spleen and kidney necrosis virus (ISKNV)-infected fish were analyzed. Overexpression of the ScSidT2 protein in fathead minnow (FHM) epithelial cells could remarkably increase the uptake of exogenous dsRNA. In tiger frog virus (TFV)-infected FHM cells, overexpression of ScSidT2 could suppress virus production, and this mechanism could be significantly enhanced by adding virus-specific dsRNA. In mandarin fish fry cells, ISKNV infection and reproduction could be promoted when the ScSidT2 protein was neutralized with specific antisera. These results suggest that ScSidT2 could be associated with the host's antiviral defense mechanism.