Genome-wide analyses of proliferation-important genes of Iridovirus-tiger frog virus by RNAi.

Tiger frog virus (TFV), a species of genus Ranavirus in the family Iridoviridae, is a nuclear cytoplasmic large DNA virus that infects aquatic vertebrates such as tiger frog (Rana tigrina rugulosa) and Chinese soft-shelled turtle (Trionyx sinensis). Based on the available genome sequences of TFV, the well-developed RNA interference (RNAi) technique, and the reliable cell line for infection model, we decided to analyze the functional importance of all predicted genes. Firstly, a relative quantitative cytopathogenic effect (Q-CPE) assay was established to monitor the viral proliferation in fish cells. Then, genome-wide RNAi screens of 95 small interference (si) RNAs against TFV were performed to characterize the functional importance of nearly all (95%) predicted TFV genes by Q-CPE scaling system. We identified 32 (33.7%) genes as essential, 50 (52.6%) genes as semi-essential and 13 (13.7%) genes as nonessential for TFV proliferation. Quantitative RT-PCR and titer assays of selected genes were performed to verify the screen results. Furthermore, the screened essential genes were analyzed for their genome distribution and conservative comparison within Ranavirus. Such a systematic screen for viral functional genes by cell phenotypes should provide further insights into understanding of the information in antiviral targets, and in viral replication and pathogenesis of iridovirus.

Immune responses of orange-spotted grouper, Epinephelus coioides, against virus-like particles of betanodavirus produced in Escherichia coli.

Betanodaviruses are the causative agents of viral nervous necrosis (VNN), a serious disease of cultured marine fish worldwide. Virus-like particles (VLPs) are one of the good novel vaccine candidates to control this disease. Until now, betanodavirus vaccine studies mainly focused on the humoral immune response and mortality after virus challenge. However, little is known about the activation of genes responsible for cellular and innate immunity by vaccines. In the present study, VLPs of orange-spotted grouper nervous necrosis virus (OGNNV) were produced in prokaryotes and their ability to enter Asian sea bass cells was the same as native virus, suggesting that they possess a similar structure to OGNNV. VLPs immunogenicity was then determined by intramuscularly vaccinating Epinephelus coioides at different concentrations (1.5 or 15 µg g(-1) fish body weight, FBW) and immunizing frequencies (administration once, twice and thrice). A single vaccination with the dosage of 1.5 µg g(-1) FBW is enough to provoke high titer antibodies (average 3 fold higher than that of negative control) with strong neutralizing antibody titer as early as 1 week post immunization. Furthermore, quantitative PCR analysis revealed that eleven genes associated with humoral, cellular and innate immunities were up-regulated in the liver, spleen and head kidney at 12h post immunization, correlating with the early antibody response. In conclusion, we demonstrated that VLP vaccination induced humoral immune responses and activated genes associated with cellular and innate immunity against betanodavirus infection in orange-spotted grouper.