Amino acidic substitutions in the polymerase N-terminal region of a reassortant betanodavirus strain causing poor adaptation to temperature increase

Temperature dependent cellular, and epigenetic regulatory mechanisms underlying the antiviral immunity in sevenband grouper to nervous necrosis virus infection

Changes in the thermal optima of fish impacts changes in the physiology and immune response associated with infections. The present study showed that at suboptimal temperatures (17 °C), the host tries to evade viral infection by downregulating the inflammatory response through enhanced neuronal protection. There was significantly less abundance of IgM + B cells in the 17 °C group compared to that in the 25 °C group. An increased macrophage population (Iba1+) during the survival phase in fish challenged at 25 °C demonstrated inflammation. Optimal temperature challenge activated virus-induced senescence in brain cells, demonstrated with a heterochromatin-associated H3K9me3 histone mark. There was an abundant expression of anti-inflammatory cytokines in the brain of fish at the suboptimal challenge. Besides the cytokines, the expression of BDNF was significantly higher in the suboptimally challenged group, suggesting that its neuronal protection activity following NNV infection is mediated through TGFβ. The suboptimal challenge resulted in H3k9ac displaying transcriptional competency, activation of trained immunity H3K4me3, and enrichment of H3 histone-lysine-4 monomethylation (H3K4me1), resulting in a robust re-stimulatory immune response. The observations from the H4 modifications showed that besides H4K12ac and H4K20m3, all the assayed modifications were significantly higher in suboptimal convalescent fishes. The suboptimally challenged fish acquired more methylation along cytosine residues than the optimally infected fish. Together, these observations suggest that optimal temperature results in an immune priming effect, whereas the protection enabled in suboptimal convalescent fishes is operated through epigenetically controlled trained immune functions.

Study on aptamer based high throughput approach identifies natural ingredients against RGNNV

Nervous necrosis virus (NNV) is one of the most destructive pathogens in marine fish aquaculture and is capable of infecting more than 50 fish species worldwide, which resulted in great economic losses. Effective drugs for managing NNV infection are urgently required. Medicinal plants have been known for thousands of years and benefit of medicinal plants against pathogens in aquaculture have emerged. Nowadays, the most commonly used method for detecting virus infection and assessing antiviral drugs efficacy is reverse transcription-quantitative real-time PCR. However, the application is limited on account of high reagent costs, complex time-consuming operations and long detection time. Aptamers have been widely applied in application of pathogens or diseases diagnosis and treatments because of high specificity, strong affinity, good stability, easy synthesized and low costs. This study aimed to establish an aptamer (GBN34)-based high-throughput screening (GBN34-AHTS) model for efficient selection and evaluation of natural ingredients against NNV infection. GBN34-AHTS is an expeditious rapid method for selecting natural ingredients against NNV, which is characterized with high-speed, dram, sensitive and accurate. AHTS strategy could reduce work intensity and experimental costs and shorten the whole screening cycle of effective ingredients. AHTS should be suitable for rapid selection of effective ingredients against other viruses, which is important for improving the prevention and controlling of aquatic diseases.

Grouper TIA-1 functions as a crucial antiviral molecule against nervous necrosis virus infection

T-cell intracellular antigen (TIA)-1 is a prion-related RNA-binding protein involved in splicing and translational repression, and regulates translation in response to stress conditions by isolating target mRNAs in stress granules (SGs). However, little is known about the potential roles of fish TIA-1 and how it works in viral infection. In this study, the TIA-1 (EcTIA-1) homolog from orange-spotted grouper (Epinephelus coioides) was cloned and characterized. The open reading frame (ORF) sequence of EcTIA-1 encoded a 388 amino acid protein with predicted molecular mass of 42.73 kDa. EcTIA-1 contains three conserved domains of RNA recognition motif (RRM) that may interact with RNA via its second and third RRMs. Overexpression of EcTIA-1 inhibited red-spotted grouper nervous necrosis virus (RGNNV) replication and positively regulated interferon immune response, which was increased by knockdown of EcTIA-1. RGNNV induced formation of SGs in cells with EcTIA-1 overexpression. These results provide a novel insight into understanding the roles of fish TIA-1 in response to RNA viruses.

Characterization of Novel Aptamers Specifically Directed to Red-Spotted Grouper Nervous Necrosis Virus (RGNNV)-Infected Cells for Mediating Targeted siRNA Delivery

Nervous necrosis virus (NNV) causes viral nervous necrosis, the most devastating disease in more than 50 fish species worldwide, with massive mortality rates up to 100%, resulting in great economic losses to mariculture. However, few methods are available for the efficient diagnosis and treatment of viral nervous necrosis. Aptamers are molecular recognition ligands characterized by their remarkably high specificity and affinity, great stability, and ease of synthesis, and have been widely studied in application of disease diagnosis and therapies. In this study, we generated three aptamers against red-spotted grouper nervous necrosis virus (RGNNV)-infected grouper brain (GB) cells using the Cell-SELEX (cell based-systematic evolution of ligands by exponential enrichment) technology. The selected aptamers formed stable stem-loop structures, and could specifically recognize RGNNV-infected GB cells, with calculated dissociation constants (K_d) of 27.96, 29.3, and 59.5 nM for aptamers GBN2, GBN10, and GBN34, respectively. They also recognized RGNNV-infected brain tissues. The three aptamers were non-toxic and showed antiviral activities both in vitro and in vivo. Fluorescence microscopy and flow cytometry also demonstrated that aptamer GBN34 could be efficiently and specifically internalized into RGNNV-infected GB cells. The targeted cellular delivery of aptamer-small interfering RNA (siRNA) conjugates remarkably inhibited RGNNV infection in GB cells. The efficiency of the aptamer-based targeted delivery system was about 75% reduction in infection after 48 h, which was similar to that of transfection. These aptamers have great potential utility in the rapid diagnosis and inhibition of RGNNV infection in mariculture.

Betanodavirus and VER Disease: A 30-year Research Review

The outbreaks of viral encephalopathy and retinopathy (VER), caused by nervous necrosis virus (NNV), represent one of the main infectious threats for marine aquaculture worldwide. Since the first description of the disease at the end of the 1980s, a considerable amount of research has gone into understanding the mechanisms involved in fish infection, developing reliable diagnostic methods, and control measures, and several comprehensive reviews have been published to date. This review focuses on host–virus interaction and epidemiological aspects, comprising viral distribution and transmission as well as the continuously increasing host range (177 susceptible marine species and epizootic outbreaks reported in 62 of them), with special emphasis on genotypes and the effect of global warming on NNV infection, but also including the latest findings in the NNV life cycle and virulence as well as diagnostic methods and VER disease control.