Identification and expression profiling analysis of grass carp Ctenopharyngodon idella LGP2 cDNA

LGP2 (laboratory of genetics and physiology 2), a homologue of RIG-I (Retinoic acid inducible gene-I) and MDA5 (Melanoma differentiation associated gene 5) without the CARD (caspase activation and recruitment domain) required for signaling, plays a pivotal role in modulating signaling by RIG-I and MDA5 for interferon (IFN) synthesis. In this study, a novel LGP2 gene from grass carp Ctenopharyngodon idella (designated as CiLGP2) was isolated and characterized. The full-length cDNA of CiLGP2 was of 2920 bp with five instability motifs (ATTTA). The open reading frame was of 2043 bp and encoded a polypeptide of 680 amino acids, including five main overlapping structural domains: two DEXDc (DEAD/DEAH box helicase domain), one ResIII (conserved restriction domain of bacterial type III restriction enzyme), one HELICc (helicase superfamily c-terminal domain) and one RD (regulatory domain). There was one more alpha-helix in the RD, compared with that in human. The CiLGP2 mRNA was ubiquitous expression in the tested tissues, was high level in spleen, skin, heart and intestine tissues, and was up-regulated by grass carp reovirus (GCRV) injection by semi-quantitative RT-PCR (sqRT-PCR) assay. The CiLGP2 expression in spleen was significantly up-regulated at 12 h (14.5 folds, P < 0.05), reached the crest at 24 h (19.0 folds, P < 0.05), and then dropped a little at 48 h (10.4 folds) post-injection of GCRV and kept this level in the following test period (P < 0.05). In liver, the temporal expression of CiLGP2 mRNA was significantly increased at 24 h (3.8 times, P < 0.05), reached peak at 48 h (10.7 times, P < 0.05), and then decreased a little bit at 72 h (5.8 times, P < 0.05) and kept this high level by the end of the test (P < 0.05). These results collectively suggested that CiLGP2 was a novel member of RLR gene family, engaging in the early stage of antiviral innate immune defense in grass carp, and laid the foundation for the further mechanism research of LGP2 in fishes.