RIG-I (
retinoic acid inducible gene-I) is a key mediator of
antiviral immunity, able to couple detection of
infection by
RNA and DNA viruses to the induction of
interferons. In the present study, a RIG-I gene from grass carp Ctenopharyngodon idella (CiRIG-I) was isolated and characterized. The full-length
cDNA of CiRIG-I was of 3198 bp and encoded a
polypeptide of 947
amino acids with an estimated molecular mass of 108,730 Da and a predicted isoelectric point of 5.85, including six main overlapping structural domains: two CARDs (caspase activation and recruitment domain), one ResIII (conserved restriction domain of bacterial type III restriction
enzyme), one DEXDc (DEAD/DEAH box helicase domain), one HELICc (helicase superfamily c-terminal domain) and one RD (regulatory domain). The CiRIG-I
mRNA was widespread expression in the tested 15 tissues by semi-quantitative RT-PCR (sqRT-PCR) assay. The CiRIG-I expressions in spleen and liver were significantly induced following grass carp reovirus (GCRV)
infection. CiRIG-I
mRNA expression was rapidly and significantly up-regulated in vitro after GCRV
infection, and the CiRIG-I transcripts were also significantly enhanced in vitro post the synthetic
double stranded RNA polyinosinic-polycytidylic
potassium salt (
poly(I:C)) stimulation. These results collectively suggested that CiRIG-I was an inducible
protein, involved in the
antiviral innate immune defense to GCRV in grass carp, and laid the foundation for the further mechanism research of RIG-I in fishes.