Abstract
Frog virus 3 (FV3) is the best characterized member of the family Iridoviridae. FV3 study has provided insights into the replication of other family members, and has served as a model of viral transcription, genome replication, and virus-mediated host-shutoff. Although the broad outlines of FV3 replication have been elucidated, the precise roles of most viral proteins remain unknown. Current studies using knock down (KD) mediated by antisense morpholino oligonucleotides (asMO) and small, interfering RNAs (siRNA), knock out (KO) following replacement of the targeted gene with a selectable marker by homologous recombination, ectopic viral gene expression, and recombinant viral proteins have enabled researchers to systematically ascertain replicative- and virulence-related gene functions. In addition, the application of molecular tools to ecological studies is providing novel ways for field biologists to identify potential pathogens, quantify infections, and trace the evolution of ecologically important viral species. In this review, we summarize current studies using not only FV3, but also other iridoviruses infecting ectotherms. As described below, general principles ascertained using FV3 served as a model for the family, and studies utilizing other ranaviruses and megalocytiviruses have confirmed and extended our understanding of iridovirus replication. Collectively, these and future efforts will elucidate molecular events in viral replication, intrinsic and extrinsic factors that contribute to disease outbreaks, and the role of the host immune system in protection from disease.
Highlights
Frog virus 3 (FV3) study has provided insights into the replication of other family members, and has served as a model of viral transcription, genome replication, and virus-mediated host-shutoff
Transcriptase, etc.) are thought to be those required for replication in all cell types, whereas those unique to a given viral species may represent specific host adaptations that contribute to virulence, host range, and immune evasion
While knock down has been achieved, we observed that inhibition of FV3 gene expression only took place if cells were infected at low multiplicities of infection, i.e.,
Summary
Frog virus 3 (FV3) is the type species of the genus Ranavirus (family Iridoviridae) [1,2,3]. Lymphocystivirus may be as large as 300 nm Consistent with this range of particle sizes, genomes, depending upon the virus, vary from 105–212 kbp and encode between 92–211 putative proteins (Table 1). Genomes of those viruses infecting fish (Lymphocystis disease virus, LCDV; Singapore grouper iridovirus, SGIV; and Epizootic haematopoietic necrosis virus, EHNV; Infectious spleen and kidney necrosis virus, ISKNV) are larger than those infecting amphibians and reptiles (FV3, soft-shelled turtle iridovirus, STIV; and Ambystoma tigrinum virus, ATV), whereas those infecting invertebrates (Invertebrate iridovirus 3, IIV-3; IIV-6, and IIV-9) are larger still. Number of putative ORFs [11,12,13,14]
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