Identification and Expression of the Laboratory of Genetics and Physiology 2 Gene in Common Carp Cyprinus Carpio
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Journal of Fish Biology (2014) doi:10.1111/jfb.12541, available online at wileyonlinelibrary.com Identification and expression of the laboratory of genetics and physiology 2 gene in common carp Cyprinus carpio X. L. Cao*†, J. J. Chen†,Y.Cao†,G.X.Nie†,Q.Y.Wan*,L.F.Wang† and J. G. Su*‡ *College of Animal Science and Technology, Northwest A&F University, Yangling 712100, People’s Republic of China and †College of Fisheries, Henan Normal University, Xinxiang 453007, People’s Republic of China (Received 29 April 2014, Accepted 9 September 2014) In this study, a laboratory of genetics and physiology 2 gene (lgp2) from common carp Cyprinus car- pio was isolated and characterized. The full-length complementary (c)DNA of lgp2 was 3061 bp and encoded a polypeptide of 680 amino acids, with an estimated molecular mass of 77 341⋅2Daanda predicted isoelectric point of 6⋅53. The predicted protein included four main overlapping structural domains: a conserved restriction domain of bacterial type III restriction enzyme, a DEAD–DEAH box helicase domain, a helicase super family C-terminal domain and a regulatory domain. Real-time quantitative polymerase chain reaction (PCR) showed widespread expression of lgp2, mitochondrial antiviral signalling protein (mavs) and interferon transcription factor 3 (irf3) in tissues of nine organs. lgp2, mavs and irf3 expression levels were significantly induced in all examined organs by infec- tion with koi herpesvirus (KHV). lgp2, mavs and irf3 messenger (m)RNA levels were significantly up-regulated in vivo after KHV infection, and lgp2 transcripts were also significantly enhanced in vitro after stimulation with synthetic, double-stranded RNA polyinosinic polycytidylic [poly(I:C)]. These findings suggest that lgp2 is an inducible protein involved in the innate immune defence against KHV in C. carpio. These results provide the basis for further research into the role and mechanisms of lgp2 in fishes. © 2014 The Fisheries Society of the British Isles Key words: gene cloning; KHV; lgp2; mRNA expression. INTRODUCTION Common carp Cyprinus carpio L. 1758 is one of the most important aquaculture fish species worldwide. Viral infections including koi C. carpio herpesvirus (KHV) have recently become a major problem in the C. carpio aquaculture industry. KHV is known to cause gill and skin damage in koi and common carp. The disease was first recog- nized in Israel and the U.S.A. (Hedricka et al., 2000), and has since has been reported in Europe, including Germany (Bretzinger et al., 1999) and the U.K. (Gilad et al., 2003). In Asia, KHV has been reported in Indonesia (Rukyani, 2002), Japan (Sano et al., 2002) and Taiwan (Tu et al., 2004) and is believed to have been imported into China. Rapid spread of the disease is associated with the import and export of ornamen- tal fish. KHV is a linear, double-stranded (ds) DNA virus with a genome of125–290 ‡Author to whom correspondence should be addressed. Tel.: +86 29 87092139; email: [email protected] 1 © 2014 The Fisheries Society of the British Isles 2 X. L. CAO ET AL. kbp contained within a T = 16 icosahedral capsid and surrounded by a proteinaceous matrix (the tegument) and a lipid envelope containing membrane-associated proteins (Zhou et al., 2000). A better understanding of the immune response of C. carpio against this virus is essential to its prevention and the development of a healthy aquaculture industry. The recognition of viruses by host cells is mediated by pathogen recognition receptors that sense virus-specific pathogen-associated molecular patterns, typically viral nucleic acids. The nucleic acid sensing transmembrane toll-like receptors (TLR), tlr3, 7, 8, and 9, localize to intracellular compartments and have well-known ligand specificities: tlr3 detects dsRNA, tlr7 and tlr8 detect single-stranded (ss) RNA and tlr9 responds to patterns found in microbial DNA and oligodeoxynucleotides encoding unmethylated CpG motifs (Takeda & Akira, 2007). In contrast, cytosolic RNA ligands are recog- nized by the retinoic acid-inducible gene-1-like receptor (RLR, rig-I) and melanoma differentiation-associated gene 5 (mda5) (Yoneyama et al., 2004, 2005). rig-I and mda5 are characterized by a core DExH box domain fused to tandem N-terminal caspase activation and recruitment domain (CARD) motifs that are essential for propagating downstream signal transduction. A third RLR-related gene, laboratory of genetics and physiology 2 (lgp2), shows high sequence similarity to mda5 and rig-I DExH box domains but lacks N-terminal CARD homology. Expression of lgp2 from a plasmid vector negatively regulates interferon (ifn) production and antiviral signalling (Rothenfusser et al., 2005; Yoneyama et al., 2005; Komuro & Horvath, 2006; Saito et al., 2007), but analyses using mice deficient in Lgp2 indicated disparate functions of Lgp2 in response to different viruses (Venkataraman et al., 2007). Recent evidence suggests that Lgp2 acts as a positive regulator of Ifn responses to diverse viruses and may act in concert with mda5 and rig-I (Saito et al., 2007). Although the structure and function of lgp2 have been described, its role in the response to DNA viruses is currently unknown. Its molecular description and expression profile have not been reported in C. carpio. In this study, the C. carpio lgp2 gene was cloned and assayed and its tissue distribu- tion and downstream associated gene mRNA expression profiles (including mavs and irf3 mRNAs, GenBank accession numbers: HQ850440.1 and HQ850443.1) analysed following KHV challenge. The lgp2 mRNA time-dependent expression in epithelioma papulosum cyprini (EPC) cells after polyinosinic polycytidylic [poly(I:C)] stimulation or KHV infection was also examined. The results of this study will provide the basis for understanding the function of lgp2 in cellular responses to dsDNA viruses, and will expand knowledge regarding innate immune mechanisms in teleosts. MATERIALS AND METHODS FISH, VIRUS DETECTION, IMMUNE CHALLENGE AND SAMPLE COLLECTION Nine month-old C. carpio were supplied by the Henan Institute of Aquaculture, Henan, China. They were maintained in indoor tanks equipped with a recirculating water system at a water temperature of 25∘ C for 7 days prior to experimentation. The fish were handled according to the guidelines of the China Law for Animal Health Protection and Instructions for Granting Permits for Animal Experimentation for Scientific Purposes [ethics approval number: SCXK (YU) 2005-0001]. © 2014 The Fisheries Society of the British Isles, Journal of Fish Biology 2014, doi:10.1111/jfb.12541 LGP2 ANTIVIRAL RESPONSE 3 The putative KHV outbreak was found when diseased fish showed clinical signs including lethargy, swimming at the water surface, dark or reddened skin, sandpaper-like skin lesions and deep-red gills with pale and white patches. KHV was confirmed by polymerase chain reaction (PCR)-based methods. DNA was extracted from gill, spleen and kidney of infected fish using DNAzol (Invitrogen; www.lifetechnologies.com), according to the manufacturer’s protocols. The specific primer set, HV-F (forward) and HV-R (reverse), developed byGray et al. (2002) was used to amplify a 290 bp fragment. DNA amplification was carried out according to the Manual of Diagnostic Tests for Aquatic Animals (Anon., 2009). The PCR product was subjected to electrophoresis, and the results were analysed by gel imaging and analysis. Cyprinus carpio showing various degrees of gill damage were used for virus isolation. Gill, kidney and spleen of diseased fish were removed aseptically and pooled, the pooled tissue was ground into a smooth paste in a cold sterile mortar, and the resultant homogenate was resus- pended in 9 ml of Hank’s balanced salt solution (HBSS, Gibco; www.lifetechnologies.com) supplemented with 2% foetal bovine serum (FBS). The tissue suspension was centrifuged (1500 g)at4∘ C for 15 min to pellet tissue debris. The clarified supernatant was diluted 1:5 (v/v) with supplemented HBSS and filtered through a⋅ 0 45 μm membrane filter to remove any bacterial contamination. The filtrate was stored at∘ 4 C for KHV challenge. For viral infection, C. carpio weighing 100–150 g were injected intraperitoneally with 4 250–300 μl of KHV at a dose of 10 tissue culture infective dose50 per g body mass. A control group was injected with an equal amount of saline. At 72 h post-infection (hpi), reverse transcription (RT)-PCR and nested PCR were performed to confirm KHV infection. Fish were anaesthetized with 100 mg l−1 of MS-222 and dissected, and tissue samples were collected at 0, 24, 48 and 72 hpi (three C. carpio for each time interval) for total RNA isolation. RNA EXTRACTION AND CDNA SYNTHESIS Total RNA extraction was performed using Triazol reagent, according to the manu- facturer’s instructions (TaKaRa; www.takara-bio.com). The quality and concentration of the total RNA were determined by gel electrophoresis and ultraviolet spectrophotometry. Three micrograms of total RNA was incubated with RNase-free DNase I (MBI Fermen- tas; www.thermoscientificbio.com) to remove genomic DNA and then reverse transcribed into cDNA using Oligo (dT) 20 primer and MMLV reverse transcriptase, according to the manufacturer’s instructions (TaKaRa). GENE CLONING AND SEQUENCING The lgp2 cDNA sequence from C. carpio was cloned using degenerate primers designed based on multiple alignments with DHX58 in zebra fish Danio rerio (Hamilton 1822) (accession number: NM-001257157.1), channel catfish Ictalurus punctatus (Rafinesque 1818) (accession number: JQ008941.1), Japanese flounder Paralichthys olivaceus (Temminck & Schlegel 1846) (accession number: HM070372.1), grass carp Ctenopharyngodon idella (Valenciennes 1844) (accession number: FJ813483.2), Atlantic salmon Salmo salar L. 1758 (accession number: BT045378.1) and goldfish Carassius auratus (L. 1758) (accession number: JF970227.1). PCR was performed with the degenerate primers LGP2F (forward) and LGP2R (reverse) (Table I), using the cDNA generated from C. carpio spleen. The PCR programme was one cycle at 94∘ C for 3 min; 35 cycles at 94∘ C for 30 s, 58∘ C for 30 s and 72∘ C for 1 min and one cycle at 72∘ C for 10 min.