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Infectious spleen and kidney necrosis virus (ISKNV) resulted in severe systemic diseases with high morbidity and mortality in Siniperca chuatsi. Vaccination is the primary method for effective prevention and control of these diseases. The development of inactivated ISKNV vaccines made some progress, but the technique of quality evaluation is scarce. Herein, a measurement of the MCP (major capsid protein) antigen concentration for the inactivated ISKNV vaccine was developed by double-antibody sandwich ELISA. Firstly, mouse monoclonal antibodies against ISKNV particles and MCP were generated. Then, a double-antibody sandwich ELISA was developed using the monoclonal antibody 1C8 1B9 as the capture antibody and Biotin-3B12 6B3 as the detection antibody. A standard curve was generated using the MCP concentration versus OD value with the linear range of concentration of 4.69~300 ng/mL. The assay sensitivity was 0.9 ng/mL. The antigen content of three batches of inactivated ISKNV vaccines was quantitatively detected using the double-antibody sandwich ELISA. The results showed that MCP antigen contents of inactivated ISKNV vaccines were positively correlated with the viral titers. The newly established double-antibody sandwich ELISA provided a useful tool for the detection of antigen quality for ISKNV inactivated vaccines. [ABSTRACT FROM AUTHOR]

The bluegill sunfish, Lepomis macrochirus , is an important aquacultural and recreational species in southern China because of its excellent taste, rapid growth rate, and good looks. At present, few pathogens are known to affect the bluegill sunfish. However, an iridovirus-like disease recently caused heavy losses to the bluegill sunfish aquaculture industry in Guangdong, China. We report that a virus, designated BSMIV-SD-20171020, was isolated from diseased bluegill sunfish in China. The isolate was efficiently propagated in a Chinese perch brain (CPB) cell line. The cytopathic effect was observed, the MCP gene PCR amplified, and the virus observed with electron microscopy. Its viral titer in CPB cells reached 104.13 TCID 50 mL−1. The mortality rate was 100% when bluegill sunfish were challenged with BSMIV-SD-20171020 at a dose of 103.13 TCID 50 /fish. A histopathological examination revealed basophilic hypertrophied cells in the intestine, liver, and spleen. A nucleotide sequence alignment and phylogenetic analysis of the major capsid protein revealed that isolate BSMIV-SD-20171020 is the species Infectious spleen and kidney necrosis virus (ISKNV), in the genus Megalocytivirus. • The ISKNV-like virus BSMIV-22SD-20171020 was firstly isolated from diseased bluegill sunfish. • The isolate is belonging to genus Megalocytivirus genotype I by MCP genes sequences analysis. • The isolate was pathogenic to the bluegill sunfish, with 100% mortality after viral infection. [ABSTRACT FROM AUTHOR]

Infectious spleen and kidney necrosis virus (ISKNV) has caused serious economic losses in the cultured mandarin fish (Siniperca chuatsi) industry in China. Host metabolism alteration induced by disease infection may be the core problem of pathogenesis. However, to date, little is known about the disease-induced fish metabolism changes. In this study, we first reported ISKNV, the fish virus, induced metabolism alteration. The metabolomics profiles of Chinese perch brain cells (CPB) post-ISKNV infection at progressive time points were analyzed using the UHPLC-Q-TOF/MS technique. A total of 98 differential metabolites were identified. In the samples harvested at 24 hours post-infection (hpi; the early stage of ISKNV infection), 49 differential metabolites were identified comparing with control cells, including 31 up-regulated and 18 down-regulated metabolites. And in the samples harvested at 72 hpi (the late stage of ISKNV infection), 49 differential metabolites were identified comparing with control cells, including 27 up-regulated and 22 down-regulated metabolites. These differential metabolites were involved in many pathways related with viral pathogenesis. Further analysis on the major differential metabolites related to glucose metabolism and amino acid metabolism revealed that both glucose metabolism and glutamine metabolism were altered and a metabolic shift was determined from glucose to glutamine during ISKNV infection cycle. In ISKNV-infected cells, CPB cells prefer to utilize glucose for ISKNV replication at the early stage of infection, while they prefer to utilize glutamine to synthetize lipid for ISKNV maturation at the late stage of infection. These findings may improve the understanding of the interaction between ISKNV and host, as well as provide a new insight for elucidating the ISKNV pathogenic mechanism. [ABSTRACT FROM AUTHOR]

Glucose is a main carbon and energy source for virus proliferation and is usually involved in the glycolysis, pentose phosphate pathway (PPP), and tricarboxylic acid cycle (TCA cycle) pathways. In this study, we investigated the roles of glucose-related metabolic pathways during the replication of infectious spleen and kidney necrosis virus (ISKNV), which has caused serious economic losses in the cultured Chinese perch (Siniperca chuatsi) industry. We found that ISKNV infection enhanced the metabolic pathways of the PPP and the TCA cycle at the early stage of the ISKNV infection cycle and enhanced the glycolysis pathway at the late stage of the ISKNV infection cycle though the comprehensive analysis of transcriptomics, proteomics, and metabolomics. The advanced results proved that ISKNV replication induced upregulation of aerobic glycolysis at the late stage of ISKNV infection cycle and aerobic glycolysis were required for ISKNV multiplication. In addition, the PPP, providing nucleotide biosynthesis, was also required for ISKNV multiplication. However, the TCA cycle involving glucose was not important and necessary for ISKNV multiplication. The results reported here provide new insights into viral pathogenesis mechanism of metabolic shift, as well as antiviral treatment strategies. [ABSTRACT FROM AUTHOR]

Epidermal growth factor receptor (EGFR) is a tyrosine kinase protein and plays a critical role in virus infection by modulating innate immunity. In this study, we cloned and sequenced the EGFR coding sequence of mandarin fish, designed as scEGFR, and explored its characteristics. scEGFR mRNA was widely expressed in the tested tissues of mandarin fish, and the higher mRNA levels were expressed in kidney and spleen. scEGFR expression was up-regulated in spleen and CPB cells at early stage of ISKNV and SCRV infection. Gefitinib (EGFR inhibitor) inhibited ISKNV and SCRV replication, and increased the expression of the interferon-stimulated genes (ISG). However the EGF (EGFR activator) promoted ISKNV and SCRV replication, and decreased the interferon-stimulated genes. Those results indicated that scEGFR and its signaling involved in ISKNV and SCRV infection, and EGFR activation negatively regulated the interferon response, providing a potential target for the development of new therapic strategy against ISKNV and SCRV. • scEGFR was widely expressed in the tested tissues of mandarin fish, especially in kidney and spleen. • scEGFR expression was up-regulated in spleen and CPB cells at early stage of ISKNV and SCRV infection. • EGFR signaling involved in ISKNV and SCRV infection by negatively regulating the interferon response. [ABSTRACT FROM AUTHOR]

Infectious spleen and kidney necrosis virus (ISKNV) is one of the major epidemiological agents that had caused great economic loss in Chinese perch ( Siniperca chuatsi ). In this study, a specific TaqMan real-time PCR was developed using a pair of primers and a TaqMan probe specific to the ORF007 gene of ISKNV to rapidly detect ISKNV copies in Chinese perch samples. This assay was optimized to produce linearity from 8.75 × 10 8 to 8.75 × 10 1 copies in standard curve with an efficiency of 98% and a R 2 value of 0.9999. Moreover, the minimum detection limit of this assay was 10,000 times more sensitive than that of conventional PCR method. The coefficients of variation of intra- and inter-assay repeatability were less than 2.4% and 3.3%, respectively. The viral distribution in different tissues of diseased Chinese perch was evaluated by TaqMan real-time PCR method and the highest level of viral copies was detected in spleen. Among the 76 diseased Chinese perch clinical samples, 35 and 29 were positive samples based on the TaqMan real-time PCR and conventional PCR methods, respectively, indicating that the TaqMan real-time PCR was more sensitive than conventional PCR. Therefore, the TaqMan real-time PCR should be a useful tool for the early surveillance and quantitation of ISKNV. [ABSTRACT FROM AUTHOR]

Co-infection with infectious spleen and kidney necrosis virus (ISKNV) and Aeromonas hydrophila is becoming ever more widespread in Chinese perch ( Siniperca chuatsi ) aquaculture industry, so that it’s necessary to develop the combined vaccine against ISKNV and A . hydrophila disease. The surface display of heterologous on bacteria using anchoring motifs from outer membranes proteins has already been explored as an effective delivery system of viral antigens. In present study, the ISKNV orf 086 gene, which is verified as a protective antigen, was inserted into omp A gene cassette of A . hydrophila GYK1 strain by homologous recombination. And an omp A- orf 086 fusion A . hydrophila mutant strain K28 was constructed. Then the ISKNV orf086 was verified to express on the surface of A . hydrophila K28 by RT-PCR, western blot and indirect immunofluorescence assay. Next, Chinese perch were intraperitoneally inoculated with formalin inactivated A . hydrophila k28 emulsified with ISA763 adjuvant with a dose of 9 × 10 8 CFU per fish. Transcriptional analysis of non-specific and specific immune related genes revealed that the expression levels of IRF-7, IRAK1, Mx, Viperin, Lysozyme and IgM were strongly up-regulated in Chinese perch post-inoculation. In addition, specific antibodies were detected by ELISA, and the results showed that antibody titer against ISKNV or A . hydrophila reached the highest with 1:800 or 1:1200 on 14dpv, respectively. Lymphocyte proliferation were detected by MTT methods, and the results showed that the SI values of AH-K28 vaccinated group to three different stimulators were significantly higher than those of control group. At last, protective efficacy were determined by challenge trials. The cumulative mortality rates of vaccinated groups were significantly lower than the control one (P < 0.05) after ISKNV or A . hydrophila challenge, and the relative percentage survival (RPS) value was 73.3% and 60%, respectively. This system provides a novel approach to the surface display of heterologous antigenic proteins on A . hydrophila and suggests the possibility to use the recombinant K28 strain as a combined vaccine against ISKNV and A . hydrophila infection. [ABSTRACT FROM AUTHOR]

The tripartite motif (TRIM) proteins play critical roles in viral infection by modulating innate immunity. However, the molecular and antiviral activity of TRIM59 in mandrain fish is not fully understood. In present study, we cloned and sequenced the TRIM59 core sequence and explored its characteristics in Mandarin fish. The Siniperca chuatsi TRIM59 (scTRIM59) showed relatively high expression in immune-related organs. scTRIM59 expression was significantly down-regulated post ISKNV infection in vivo and vitro, but up-regulated at the early stages of SCRV infection in CPB cells. The overexpression of scTRIM59 inhibited ISKNV and SCRV infection, but decreased the expression of IRF3/IRF7-mediated signal genes. However, knockdown of scTRIM59 promoted the ISKNV and SCRV infection, but increased the expression of IRF3/IRF7-mediated signal genes. Those results indicated that scTRIM59 negatively regulated ISKNV, SCRV infection and IRF3/IRF7-mediated signal genes. This study provided new ideas about the function of scTRIM59. • scTRIM59 was widely expressed in the tissues of mandarin fish, especially in immune organs. • scTRIM59 expression was down-regulated post ISKNV infection, however, scTRIM59 was up-regulated post SCRV infection. • scTRIM59 negatively regulated ISKNV, SCRV infection and IRF3/IRF7-mediated signal genes. [ABSTRACT FROM AUTHOR]

The PI3K/AKT/p53 signaling pathway is activated by various types of cellular stimuli or pathogenic infection, and then regulates fundamental cellular functions to combat these stimulations. Here, we studied the meaningful roles of PI3K/AKT/p53 in regulating cellular machine such as autophagy, immune responses, as well as antiviral activity in Chinese perch brain (CPB) cells infected by infectious spleen and kidney necrosis virus (ISKNV), which is an agent caused devastating losses in mandarin fish (Siniperca chuatsi) industry. We found that ISKNV infection induced up-regulation of host PI3K/AKT/p53 axis, but inhibited autophagy in CPB cells. Interestingly, activation of PI3K/AKT/p53 axis factors trough agonists or overexpression dramatically decreased host autophagy level, inhibited ISKNV replication, and elevated the expression of immune-related genes in CPB cells. In contrast, suppression of PI3K/AKT/p53 pathway by inhibitors or small interfering RNA (siRNA)-mediated gene silence increased the autophagy and ISKNV replication, but down-regulated immune responses in CPB cells. All these results indicate that PI3K/AKT/p53 pathway plays an important role in anti-ISKNV infection and can be used as a new target for controlling ISKNV disease. • ISKNV infection induced up-regulation of PI3K/AKT/p53 axis, but inhibited autophagy in CPB cells. • Activation of PI3K/AKT/p53 axis factors decreased autophagy level and inhibited ISKNV replication in CPB cells. • Suppression of PI3K/AKT/p53 pathway increased the autophagy and ISKNV replication in CPB cells. • The PI3K/AKT/p53 pathway promotes the expression of immune-related genes in ISKNV-infected CPB cells. [ABSTRACT FROM AUTHOR]

c-Myc is a transcription factor and master regulator of cellular metabolism, and plays a critical role in virus replication by regulating glutamine metabolism. In this study, the open-reading frame (ORF) of c-Myc, designated as Sc-c-Myc, was cloned and sequenced. Multiple alignment of the amino acid sequence showed that the conserved domain of Sc-c-Myc, including the helix–loop–helix-zipper (bHLHzip) domain and Myc N-terminal region, shared high identities with other homologues from different species. Sc-c-Myc mRNA was widely expressed in the examined tissues of mandarin fish, and the higher mRNA levels was expressed in hind kidney. Moreover, mRNA and protein level of Sc-c-Myc was significantly increased in the Chinese perch brain (CPB) cells and spleen of mandarin fish post infection with infectious spleen and kidney necrosis virus (ISKNV) and Siniperca chuatsi rhabdovirus (SCRV). Sc-c-Myc overexpression promoted ISKNV and SCRV replication, on the contrary, knocking down Sc-c-Myc restrained ISKNV and SCRV replication. These results indicated that Sc-c-Myc involved in ISKNV and SCRV replication and proliferation, providing a potential target for the development of new therapic strategy against ISKNV and SCRV. • Sc-c-Myc ORF of mandarin fish (Siniperca chuatsi) (Sc-c-Myc) was cloned and characterized. • Sc-c-Myc expression was up-regulated in spleen and CPB cells after ISKNV and SCRV infection. • Sc-c-Myc overexpression increased ISKNV and SCRV yield; Sc-c-Myc knockdown decreased ISKNV and SCRV yield. [ABSTRACT FROM AUTHOR]

Autophagy plays important functions in viral replication and pathogenesis. In this study, we investigated the role of autophagy in the replication of infectious kidney and spleen necrosis virus (ISKNV), an agent that has caused devastating losses in Chinese perch ( Siniperca chuatsi ) industry. We found that ISKNV infection triggered the complete autophagic process, as demonstrated by microtubule-associated protein 1 light chain 3B II (LC3B-II) conversion, an increased accumulation of punctate GFP-LC3-expressing cells, a higher number of autophagosome-double-membrane vesicles in the cytoplasm, and increased levels of autophagic flux in CPB cells. Then, we investigated the role of autophagy in the process of ISKNV replication. Results showed that inducing autophagy by rapamycin promoted ISKNV replication and proteins synthesis but decreased extracellular virus yields. While, blocking autophagosome-lysosome fusion by chloroquine (CQ) promoted infectious virus yields in culture supernatant. These results offer insight into the complex interactions between ISKNV and host cell, providing new insights into viral pathogenesis and antiviral treatment strategies. [ABSTRACT FROM AUTHOR]

In recent years, the tumor suppressor protein p53, which is crucial for cellular defense against tumor development, has also been implicated in host antiviral defense. In the present study, a 1555 bp full-length cDNA of p53 from mandarin fish ( Siniperca chuatsi ) (Sc-p53) was cloned and characterized. Quantitative real-time PCR assays revealed that Sc-p53 was expressed in all tissues examined, and it was most abundant in the gill and kidney. Recombinant Sc-p53 fused with a His·Tag was expressed in Escherichia coli BL21 (DE3) cells and a rabbit polyclonal antibody was raised against recombinant Sc-p53. In addition, the regulation of Sc-p53 gene expression after experimental viral infection was determined and characterized. The mRNA and protein expression of Sc-p53 were significantly up-regulated in the Chinese perch brain (CPB) cell line and mandarin fish after infection with infectious kidney and spleen necrosis virus (ISKNV). The results showed a biphasic expression pattern of Sc-p53 protein in CPB. However, a different expression pattern of Sc-p53 in response to S. chuatsi rhabdovirus (SCRV) infection was found. The mRNA expression of Sc-p53 was significantly up-regulated in CPB at 6 h and spleen of mandarin fish at 24 h post-infection. The protein expression of Sc-p53 was significantly up-regulated in CPB at 1 h, remained elevated at 4 h, and then decreased to control level at 8 h post-infection by SCRV. All of these data suggested that Sc-p53 plays a critical role in immune defense and antiviral responses. [ABSTRACT FROM AUTHOR]

Glutaminolysis plays a critical role in viral replication. While Glutaminase 1 (GLS1) is a key enzyme in the glutaminolysis pathway. However the characteristic and function of GLS1 in mandarin fish during viral infection remains largely unknown. In the present study, the full-length cDNA of GLS1, designated as Sc-GLS1, was cloned from mandarin fish (Siniperca chuatsi) with an open-reading frame of 1920 bp, and encoded a 639 amino acid polypeptide with 5′ and 3′ untranslated regions of 115 and 1287 bp, respectively. Multiple alignment of the amino acid sequence showed that Sc-GLS1 shared high identities with other homologues from different species. Sc-GLS1 protein has the typical conserved domains including the glutaminase domain and the ankyrin domain. Quantitative real-time PCR (qPCR) assay revealed that Sc-GLS1 was ubiquitously expressed in all tissues examined, and it was most abundant in the hind kidney. In addition, mRNA and protein level of Sc-GLS1 was significantly up-regulated with a biphasic expression pattern in the Chinese perch brain (CPB) cell line and the spleen of mandarin fish post infection by infectious kidney and spleen necrosis virus (ISKNV). And Sc-GLS1 expression in mRNA and protein level was also significantly up-regulated in CPB cells and the spleen of mandarin fish post infection by Siniperca chuatsi rhabdovirus (SCRV). After knocking down Sc-GLS1 with siRNA or inhibiting Sc-GLS1 activity with BPTES, protein expression and yields of ISKNV and SCRV were significantly decreased determined by western blotting and qPCR. These findings provided more information of GLS1 for further insight into virus-induced host metabolism alteration. • GLS1 cDNA of mandarin fish (Siniperca chuatsi) (Sc-GLS1) was cloned and characterized. • Sc-GLS1 mRNA and protein expression was up-regulated after ISKNV or SCRV infection. • Inhibiting Sc-GLS expression and activity decreased ISKNV and SCRV yield. [ABSTRACT FROM AUTHOR]