Meta-analysis of honey bee neurogenomic response links Deformed wing virus type A to precocious behavioral maturation

Crop pollination by the western honey bee Apis mellifera is vital to agriculture but threatened by alarmingly high levels of colony mortality, especially in Europe and North America. Colony loss is due, in part, to the high viral loads of Deformed wing virus (DWV), transmitted by the ectoparasitic mite Varroa destructor, especially throughout the overwintering period of a honey bee colony. Covert DWV infection is commonplace and has been causally linked to precocious foraging, which itself has been linked to colony loss. Taking advantage of four brain transcriptome studies that unexpectedly revealed evidence of covert DWV-A infection, we set out to explore whether this effect is due to DWV-A mimicking naturally occurring changes in brain gene expression that are associated with behavioral maturation. Consistent with this hypothesis, we found that brain gene expression profiles of DWV-A infected bees resembled those of foragers, even in individuals that were much younger than typical foragers. In addition, brain transcriptional regulatory network analysis revealed a positive association between DWV-A infection and transcription factors previously associated with honey bee foraging behavior. Surprisingly, single-cell RNA-Sequencing implicated glia, not neurons, in this effect; there are relatively few glial cells in the insect brain and they are rarely associated with behavioral plasticity. Covert DWV-A infection also has been linked to impaired learning, which together with precocious foraging can lead to increased occurrence of infected bees from one colony mistakenly entering another colony, especially under crowded modern apiary conditions. These findings provide new insights into the mechanisms by which DWV-A affects honey bee health and colony survival.

Tributyltin exposure increases mortality of nodavirus infected Japanese medaka Oryzias latipes larvae

We investigated the effect of combined exposure to nodavirus infection and TBT on medaka (Oryzias latipes). Medaka larvae were infected by immersion in medium containing nodavirus at titers of 10^2.5, 10^3.5, or 10^4.5 TCID₅₀/mL. Infected fish then were exposed to TBT at 0, 0.17, 0.52, 1.6, or 4.7μg/L. Of the 12 groups exposed to both stressors, the mortalities of 6 (10^2.5 TCID₅₀/mL+0.52, 1.6, or 4.7μg/L, 10^3.5 TCID₅₀/mL+4.7μg/L and 10^4.5 TCID₅₀/mL+1.6 or 4.7μg/L) were significantly higher than that of each TBT control. Specifically, mortality was 46±5.5% in the group exposed to both 10^2.5 TCID₅₀/mL virus and 0.52μg/L TBT, which represent the lowest observed effective dose and concentration, respectively, among the 6 groups with increased mortalities. Our results suggest that combined exposure to both stressors suppresses antiviral mechanisms in the fish, thus increasing mortality.

Order reduction for an RNA virus evolution model

A mathematical or computational model in evolutionary biology should necessary combine several comparatively fast processes, which actually drive natural selection and evolution, with a very slow process of evolution. As a result, several very different time scales are simultaneously present in the model; this makes its analytical study an extremely difficult task. However, the significant difference of the time scales implies the existence of a possibility of the model order reduction through a process of time separation. In this paper we conduct the procedure of model order reduction for a reasonably simple model of RNA virus evolution reducing the original system of three integro-partial derivative equations to a single equation. Computations confirm that there is a good fit between the results for the original and reduced models.

Involvement of fish signal transducer and activator of transcription 3 (STAT3) in nodavirus infection induced cell death

The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway is an important signaling pathway activated by interferons in response to virus infection. Fish STAT3 has been demonstrated to be involved in Singapore grouper iridovirus (SGIV) infection and virus induced paraptosis, but its effects on the replication of other fish viruses still remained uncertain. Here, the roles of grouper STAT3 (Ec-STAT3) in red spotted grouper nervous necrosis virus (RGNNV) infection were investigated. The present data showed that the distribution of phosphorylated Ec-STAT3 was altered in RGNNV infected fish cells, and the promoter activity of STAT3 was significantly increased during virus infection, suggesting that STAT3 activation was involved in RGNNV infection. Using STAT3 specific inhibitor, we found that inhibition of Ec-STAT3 in vitro did not affect the transcription and protein synthesis of RGNNV coat protein (CP), however, the severity of RGNNV induced vacuolation and autophagy was significantly increased. Meanwhile, at the late stage of virus infection, RGNNV induced necrotic cell death was significantly decreased after inhibition of Ec-STAT3. Further studies indicated that Ec-STAT3 inhibition significantly increased the transcript level of autophagy related genes, including UNC-51-like kinase 2 (ULK2) and microtubule-associated protein 1 light chain 3-II (LC3-II) induced by RGNNV infection. Moreover, the expression of several pro-inflammatory factors, including TNFα, IL-1β and IL-8 were mediated by Ec-STAT3 during RGNNV infection. Together, our results not only firstly revealed that STAT3 exerted novel roles in response to fish virus infection, but also provided new insights into understanding the roles of STAT3 in different forms of programmed cell death.

Novel respiratory viruses: what should the clinician be alert for?

Since 1990, several novel respiratory viruses affecting humans have been described. In this review, we focus on three pathogens that have caused significant human mortality and raise important public health concerns: severe acute respiratory syndrome (SARS)-coronavirus, Middle East respiratory syndrome (MERS)-coronavirus and avian influenza A viruses (H5N1 and H7N9). Novel respiratory viruses have the potential to instil fear in the public and physicians alike if they are associated with a high case fatality rate. Those viruses with a significant potential for onward human-to-human transmission (including in healthcare settings) might present significant challenges for national public health services and local hospital infection control.

RNA recognition and signal transduction by RIG-I-like receptors

Viral infection is detected by cellular sensor molecules as foreign nucleic acids and initiates innate antiviral responses, including the activation of proinflammatory cytokines and type I interferon (IFN). Recent identification of cytoplasmic viral sensors, such as retinoic acid-inducible gene-I-like receptors (RLRs), highlights their significance in the induction of antiviral innate immunity. Moreover, it is intriguing to understand how they can discriminate endogenous RNA from foreign viral RNA and initiate signaling cascades leading to the induction of type I IFNs. This review focuses on the current understanding of the molecular machinery underlying RNA recognition and subsequent signal transduction by RLRs.

Approaching the RNA ligand for RIG-I?

Innate and antigen-specific antiviral immunity are triggered by immunorecognition of viral nucleic acids. The helicase retinoic acid-inducible gene I (RIG-I) (also known as DDX58) is the key sensor of negative strand RNA viruses in the cytosol of cells. RNA containing a triphosphate at the 5'-end was shown to activate RIG-I, but the exact structure of RNA supporting 5'-triphosphate recognition, the requirement of a 5'-triphosphate group, as well as the existence of RNA structures detected by RIG-I in the absence of 5'-triphosphate remain controversial. Here, we revisit the literature on RIG-I and RIG-I ligands. The literature proposes at least six different RIG-I ligands: (i) single strand with a 5'-triphosphate, (ii) double-stranded RNA with a 5'-triphosphate, (iii) 5'-triphosphate single-stranded RNA with A- and U-rich 3'-sequences, (iv) double-stranded RNA of intermediate length (>300 and <2000 bp) without 5'-triphosphate, (v) blunt-end short double-stranded RNA (23-30 bp) without 5'-triphosphate, and (vi) short double-stranded RNA (23-30 bp) with 5'-monophosphate. RIG-I thus seems promiscuous for a variety of different RNA molecules, very similar to the Toll-like receptors, of which 10 family members are sufficient for the safe detection of the microbial cosmos. In the light of these outstanding publications, it seems an unlikely possibility that there is a fundamental shortcoming in the design of all studies. Looking closely, the only issue that comes to mind is the in vitro transcription technique used by all investigators without confirming the identity of RNA products. This technique, together with the different biological systems used, the lack of dose responses and of proper comparison of different published ligands and controls leave us with more questions than answers as to what the exact RIG-I ligand is, if in fact it exists.

Innate immunity to virus infection

The innate immune system is essential for the initial detection of invading viruses and subsequent activation of adaptive immunity. Three classes of receptors, designated retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), Toll-like receptors (TLRs), and nucleotide oligomerization domain (NOD)-like receptors (NLRs), sense viral components, such as double-stranded RNA (dsRNA), single-stranded RNA, and DNA. RLRs and TLRs play essential roles in the production of type I interferons (IFNs) and proinflammatory cytokines in cell type-specific manners. While the RLRs play essential roles in the recognition of RNA viruses in various cells, plasmacytoid dendritic cells utilize TLRs for detecting virus invasion. NLRs play a role in the production of mature interleukin-1 beta to dsRNA stimulation. Activation of innate immune cells is critical for mounting adaptive immune responses. In this review, we discuss recent advances in our understanding of the mechanisms of viral RNA recognition by these different types of receptors and its relation to acquired immune responses.

Animal models of highly pathogenic RNA viral infections: encephalitis viruses

The highly pathogenic RNA viruses that cause encephalitis include a significant number of emerging or re-emerging viruses that are also considered potential bioweapons. Many of these viruses, including members of the family Flaviviridae, the genus Alphavirus in the family Togaviridae, and the genus Henipavirus in the family Paramyxoviridae, circulate widely in their endemic areas, where they are transmitted by mosquitoes or ticks. They use a variety of vertebrate hosts, ranging from birds to bats, in their natural life cycle. As was discovered in the United States, the introduction of a mosquito-borne encephalitis virus such as West Nile virus can cause significant health and societal concerns. There are no effective therapeutics for treating diseases caused by any of these viruses and there is limited, if any, vaccine availability for most. In this review we provide a brief summary of the current status of animal models used to study highly pathogenic encephalitic RNA viruses for the development of antiviral therapeutics and vaccines.

RNA viruses: hijacking the dynamic nucleolus

The nucleolus is a dynamic subnuclear structure that is crucial to the successful functioning of a cell. Its functions include ribosomal RNA synthesis, cell growth and cell-cycle control as well as responding to cellular stress.

Recent studies show that the nucleolus is not a steady-state structure but instead is made up of numerous protein–protein and protein–nucleic-acid interactions that are constantly changing in response to the metabolic conditions of the cell.

Many different viruses target the nucleolus to disrupt host-cell function and to recruit cellular proteins to aid in virus replication.

The study of viral-protein trafficking to the nucleolus and the interaction of viral proteins with nucleolar proteins is providing many insights into the cell biology of the nucleolus.

Because the nucleolus is fundamental to the life cycle of many viruses, disrupting the interaction between the nucleolus and the virus could lead to the design of novel therapeutic strategies.

RNA viruses, particularly positive-strand RNA viruses, interact with the nucleolus to usurp host-cell functions and recruit nucleolar proteins to facilitate virus replication. Here, Julian Hiscox reviews the latest data on RNA-virus interactions with this dynamic subnuclear structure.

The nucleolus is a dynamic subnuclear structure with roles in ribosome subunit biogenesis, mediation of cell-stress responses and regulation of cell growth. The proteome and structure of the nucleolus are constantly changing in response to metabolic conditions. RNA viruses interact with the nucleolus to usurp host-cell functions and recruit nucleolar proteins to facilitate virus replication. Investigating the interactions between RNA viruses and the nucleolus will facilitate the design of novel anti-viral therapies, such as recombinant vaccines and therapeutic molecular interventions, and also contribute to a more detailed understanding of the cell biology of the nucleolus.

Betanodavirus infection in the freshwater model fish medaka (Oryzias latipes)

Betanodaviruses, the causal agents of viral nervous necrosis in marine fish, have bipartite, positive-sense RNA genomes. As their genomes are the smallest and simplest among viruses, betanodaviruses have been studied in detail as model viruses by using a genetic-engineering system, as has occurred with the insect alphanodaviruses, the other members of the family Nodaviridae. However, studies of virus–host interactions have been limited, as betanodaviruses basically infect marine fish at early developmental stages (larval and juvenile). These fish are only available for a few months of the year and are not suitable for the construction of a reverse-genetics system. To overcome these problems, several freshwater fish species were tested for their susceptibility to betanodaviruses. It was found that adult medaka (Oryzias latipes), a well-known model fish, was susceptible to both Striped jack nervous necrosis virus (the type species of the genus Betanodavirus) and Redspotted grouper nervous necrosis virus (RGNNV), which have different host specificities in marine fish species. Infected medaka exhibited erratic swimming and the viruses were localized specifically in the brain, spinal cord and retina of the infected fish, similar to the pattern of infection in naturally infected marine fish. Moreover, medaka were susceptible to RGNNV at the larval stage. This is the first report of a model virus–model host infection system in fish. This system should facilitate elucidation of the mechanisms underlying RNA virus infections in fish.

Chronic bronchitis: the role of viruses

Mucus is produced by the epithelial cells in the glands, gland ducts, and the cells lining the airway lumen in the lower airways. The chronic cough and sputum production that defines chronic bronchitis is associated with an inflammatory reaction involving this mucus-secreting apparatus. Respiratory viral infections target the epithelial cells of the lung producing desquamation, microvascular dilatation, edema, and an inflammatory cell infiltrate. These changes predispose the lower airways to bacterial infection by interfering with mucociliary clearance and reducing bacterial killing by macrophages. The exact role of those infections in the pathogenesis of chronic bronchitis has not been clearly determined but they probably play a critical role in inducing bacterial colonization and initiating acute exacerbations of COPD. This article reviews the classification of the viral agents responsible for respiratory tract infection and the nature of the changes they produce in the normal airways and in the airways of patients with chronic bronchitis during acute infections.

Respiratory viruses and asthma

Viral infections have become increasingly recognized as a significant cause of asthma exacerbations, mainly because of improved viral detection techniques. Unfortunately, the ability to specifically treat viral infections and to limit the asthma morbidity associated with these agents has not kept pace with diagnostic technology. This article focuses on current concepts of the epidemiology of viruses in asthma exacerbations, investigations studying the physiologic and immunologic consequences of viral infection, and potential therapies to minimize virally-induced airway hyperresponsiveness. To impact this significant health problem, researchers must definitively ascertain the mechanisms by which viruses induce airway reactivity and must develop rational, safe approaches to prevent the consequences of viral infection in the patient with asthma.