The Jak-STAT signaling pathway is required but not sufficient for the antiviral response of drosophila

An evolutionary perspective to innate antiviral immunity in animals

Viruses pose a significant threat to cellular organisms. Innate antiviral immunity encompasses both RNA- and protein-based mechanisms designed to sense and respond to infections, a fundamental aspect present in all living organisms. A potent RNA-based antiviral mechanism is RNA interference, where small RNA-programmed nucleases target viral RNAs. Protein-based mechanisms often rely on the induction of transcriptional responses triggered by the recognition of viral infections through innate immune receptors. These responses involve the upregulation of antiviral genes aimed at countering viral infections. In this review, we delve into recent advances in understanding the diversification of innate antiviral immunity in animals. An evolutionary perspective on the gains and losses of mechanisms in diverse animals coupled to mechanistic studies in model organisms such as the fruit fly Drosophila melanogaster is essential to provide deep understanding of antiviral immunity that can be translated to new strategies in the treatment of viral diseases.

Protein-coding circular RNA enhances antiviral immunity via JAK/STAT pathway in Drosophila

RNA interference (RNAi) drives powerful antiviral immunity in plants and animals so that many viruses must express viral suppressor of RNAi (VSR) to establish virulent infection. However, little is known about the immune responses conferring resistance against viruses that have evolved the counter-defensive strategy to suppress antiviral RNAi. In this study, we discover that Drosophila cells infected with Drosophila C virus (DCV), a natural viral pathogen of Drosophila known to harbor a potent VSR, exhibit heightened expression of circular RNA circZfh1. circZfh1 confers virus resistance in the presence of viral suppression of antiviral RNAi. Furthermore, we validate that circZfh1 encodes a 274-amino acid protein, CRAV, essential for its antiviral activity. Notably, CRAV differs from its parental Zfh1 gene in a different reading frame, with the C-terminal 69 amino acids unique to CRAV. Our analysis also reveals the presence of CRAV in species within the melanogaster subgroup, with the C-terminal unique fragment undergoing accelerated evolution. Expression of CRAV upregulates the expression of the cytokine Upd3, which binds to its receptor, stimulating the JAK-STAT pathway and enhancing the immune response to DCV infection. Notably, CRISPR/Cas9 knockout of circZfh1 significantly enhances DCV replication in vitro and in vivo, with circZfh1-knockout adult flies displaying heightened disease susceptibility to DCV. In summary, our findings unveil a Drosophila protein-coding circular RNA that activates an innate immune signaling pathway crucial for virus resistance following the suppression of antiviral RNAi by viruses, thereby elucidating a novel counter-defensive strategy.IMPORTANCEEukaryotic hosts possess a complex, multilayered immune system that guards against pathogen invasion. In fruit flies, RNA interference (RNAi) drives robust antiviral immunity, prompting many viruses to express viral suppressors of RNAi (VSRs) to establish virulent infections. However, little is known about immune responses that confer resistance against viruses with potent VSRs. In this study, we discovered that Drosophila cells infected with Drosophila C virus (DCV), a natural viral pathogen possessing a potent VSR, upregulated the expression of circular RNA circZfh1. circZfh1 exhibits DCV-specific antiviral activity, encoding a 274-amino acid protein, CRAV, crucial for its antiviral effects. As a different reading frame from its parental Zfh1 gene, the C-terminal 69 amino acids are unique to CRAV, undergoing faster evolution. CRAV activates the JAK-STAT pathway, enhancing the immune response to DCV infection. Therefore, our work uncovers a new strategy for suppressing viral counter-defense through protein-coding circular RNA in fruit flies.

Tripartite interactions between viruses, parasites, and mosquitoes

Mosquito-borne diseases have a major impact on global human health. Biological agents that colonize the mosquito vector are increasingly explored as an intervention strategy to prevent vector-borne disease transmission. For instance, the release of mosquitoes carrying the endosymbiotic bacterium Wolbachia effectively reduced dengue virus incidence and disease. Insect-specific viruses are likewise considered as biocontrol agents against vector-borne diseases. While most studies focused on insect-specific viruses as an intervention against arthropod-borne viruses, we here consider whether mosquito-specific viruses may affect the transmission of the malaria-causing Plasmodium parasite by Anopheles mosquitoes. Although there is no direct experimental evidence addressing this question, we found that viral infections in dipteran insects activate some of the immune pathways that are antiparasitic in Anopheles. These findings suggest that indirect virus-parasite interactions could occur and that insect-specific viruses may modulate malaria transmission. Tripartite interactions between viruses, parasites, and Anopheles mosquitoes thus merit further investigation.

Detection of Known and Novel Virus Sequences in the Black Solider Fly and Expression of Host Antiviral Pathways

The mass rearing of animals in close quarters can be highly conducive to microbe transmission, including pathogens. This has been shown multiple times in the case of important industrial insects such as crickets, silkworms, and honeybees. One industrial insect of increasing importance is the black soldier fly (Diptera: Hermetia illucens), as it can convert organic waste into high-quality protein and fatty acids. Along with this, they take up far less space than traditional protein sources, as millions of black soldier flies can be reared in a relatively small facility. Because of this, there is a growing interest in the pathogens that could impact black soldier fly-rearing efforts. So far, only three black soldier fly-associated viruses have been identified. We used metatranscriptomic sequencing to survey black soldier fly guts, frass, and diet for viruses. We detected sequences from two novel viruses. One, which we name Hermetia illucens sigma-like virus 1, is phylogenetically related to viruses of the genus Sigmavirus, which have been highly studied in Drosophila. The other novel virus, which we name Hermetia illucens inse-like virus 1, is the second double-stranded RNA virus of the order Ghabrivirales described in the black soldier fly, and groups within a new family of insect viruses called the Inseviridae. We also detected two black soldier fly-associated viruses previously identified by our group: BSF nairo-like virus 1 and BSF uncharacterized bunyavirus-like 1. Consistent with our previous study, these two viruses are found primarily in frass samples and occur together more often than expected at random. When analyzing host transcription, we found significant differences in gene expression for eight candidate antiviral genes in the black soldier fly when comparing samples with and without viral sequences. Our results suggest that black soldier fly-virus interactions are ongoing, and they could be of interest to black soldier fly producers.

Deformed wing virus genotypes A and B do not elicit immunologically different responses in naïve honey bee hosts

Iflavirus aladeformis (Picornavirales: Iflaviridae), commonly known as deformed wing virus(DWV), in association with Varroa destructor Anderson and Trueman (Mesostigmata: Varroidae), is a leading factor associated with honey bee (Apis mellifera L. [Hymenoptera: Apidae]) deaths. The virus and mite have a near global distribution, making it difficult to separate the effect of one from the other. The prevalence of two main DWV genotypes (DWV-A and DWV-B) has changed over time, leading to the possibility that the two strains elicit a different immune response by the host. Here, we use a honey bee population naïve to both the mite and the virus to investigate if honey bees show a different immunological response to DWV genotypes. We examined the expression of 19 immune genes by reverse transcription quantitative PCR (RT-qPCR) and analysed small RNA after experimental injection with DWV-A and DWV-B. We found no evidence that DWV-A and DWV-B elicit different immune responses in honey bees. RNA interference genes were up-regulated during DWV infection, and small interfering RNA (siRNA) responses were proportional to viral loads yet did not inhibit DWV accumulation. The siRNA response towards DWV was weaker than the response to another honey bee pathogen, Triatovirus nigereginacellulae (Picornavirales: Dicistroviridae; black queen cell virus), suggesting that DWV is comparatively better at evading host antiviral defences. There was no evidence for the production of virus-derived Piwi-interacting RNAs (piRNAs) in response to DWV. In contrast to previous studies, and in the absence of V. destructor, we found no evidence that DWV has an immunosuppressive effect. Overall, our results advance our understanding of the immunological effect that DWV in isolation elicits in honey bees.

Infection and chronic disease activate a systemic brain-muscle signaling axis

Infections and neurodegenerative diseases induce neuroinflammation, but affected individuals often show nonneural symptoms including muscle pain and muscle fatigue. The molecular pathways by which neuroinflammation causes pathologies outside the central nervous system (CNS) are poorly understood. We developed multiple models to investigate the impact of CNS stressors on motor function and found that Escherichia coli infections and SARS-CoV-2 protein expression caused reactive oxygen species (ROS) to accumulate in the brain. ROS induced expression of the cytokine Unpaired 3 (Upd3) in Drosophila and its ortholog, IL-6, in mice. CNS-derived Upd3/IL-6 activated the JAK-STAT pathway in skeletal muscle, which caused muscle mitochondrial dysfunction and impaired motor function. We observed similar phenotypes after expressing toxic amyloid-β (Aβ42) in the CNS. Infection and chronic disease therefore activate a systemic brain-muscle signaling axis in which CNS-derived cytokines bypass the connectome and directly regulate muscle physiology, highlighting IL-6 as a therapeutic target to treat disease-associated muscle dysfunction.

Viral infection disrupts intestinal homeostasis via Sting-dependent NF-κB signaling in Drosophila

Host-microbe interactions influence intestinal stem cell (ISC) activity to modulate epithelial turnover and composition. Here, we investigated the functional impacts of viral infection on intestinal homeostasis and the mechanisms by which viral infection alters ISC activity. We report that Drosophila A virus (DAV) infection disrupts intestinal homeostasis in Drosophila by inducing sustained ISC proliferation, resulting in intestinal dysplasia, loss of gut barrier function, and reduced lifespan. We found that additional viruses common in laboratory-reared Drosophila also promote ISC proliferation. The mechanism of DAV-induced ISC proliferation involves progenitor-autonomous epidermal growth factor receptor (EGFR) signaling, c-Jun N-terminal kinase (JNK) activity in enterocytes, and requires Sting-dependent nuclear factor κB (NF-κB) (Relish) activity. We further demonstrate that activating Sting-Relish signaling is sufficient to induce ISC proliferation, promote intestinal dysplasia, and reduce lifespan in the absence of infection. Our results reveal that viral infection can significantly disrupt intestinal physiology, highlight a novel role for Sting-Relish signaling, and support a role for viral infection in aging.

Drosophila melanogaster Toll-9 elicits antiviral immunity against Drosophila C virus

The Toll pathway plays a pivotal role in innate immune responses against pathogens. The evolutionary conserved pathogen recognition receptors (PRRs), including Toll like receptors (TLRs), play a crucial role in recognition of pathogen associated molecular patterns (PAMPs). The Drosophila genome encodes nine Toll receptors that are orthologous to mammalian TLRs. While mammalian TLRs directly recognize PAMPs, most Drosophila Tolls recognize the proteolytically cleaved ligand Spätzle to activate downstream signaling cascades. In this study, we demonstrated that Toll-9 is crucial for antiviral immunity against Drosophila C virus (DCV), a natural pathogen of Drosophila . A transposable element insertion in the Toll-9 gene renders the flies more susceptible to DCV. The stable expression of Toll-9 in S2 cells confers resistance against DCV infection by upregulation of the RNAi pathway. Toll-9 promotes the dephosphorylation of AKT, resulting in the induction of antiviral RNAi genes to inhibit DCV replication. Toll-9 localizes to the endosome where it binds dsRNA, suggesting its role to detect viral dsRNA. Toll-9 also induces apoptosis during DCV infection, contributing to its antiviral role. Together, this work identifies the role of Toll-9 in antiviral immunity against DCV infection through its ability to bind dsRNA and induce AKT-mediated RNAi antiviral immunity.

IMPORTANCE

Insects rely on innate immunity and RNA interference (RNAi) to combat viral infections. Our study underscores the pivotal role of Drosophila Toll-9 in antiviral immunity, aligning with findings in Bombyx mori , where Toll-9 activation upregulates the RNAi component Dicer2 . We demonstrate that Drosophila Toll-9 functions as a pattern recognition receptor (PRR) for double-stranded RNA (dsRNA) during Drosophila C virus (DCV) infection, akin to mammalian TLRs. Toll-9 activation leads to the upregulation of key RNAi components, Dicer2 and Argonaute2 , and dephosphorylation of AKT triggers apoptosis via induction of proapoptotic genes Hid and Reaper . This study also reveals that Toll-9 localizes in endosomal compartments where it interacts with dsRNA. These insights enhance our understanding of Drosophila innate immune mechanisms, reflecting the evolutionary conservation of immune responses across diverse species and providing impetus for further research into the conserved roles of TLRs across the animal kingdom.

Drosophila melanogaster Limostatin and Its Human Ortholog Promote West Nile Virus Infection

The arbovirus West Nile virus (WNV) is a danger to global health. Spread primarily by mosquitoes, WNV causes about 2000 cases per year in the United States. The natural mosquito immune response controls viral replication so that the host survives but can still transmit the virus. Using the genetically malleable Drosophila melanogaster model, we previously dissected innate immune pathways used to control WNV infection. Specifically, we showed that insulin/IGF-1 signaling (IIS) activates a JAK/STAT-mediated immune response that reduces WNV. However, how factors that regulate IIS in insects control infection has not been identified. D. melanogaster Limostatin (Lst) encodes a peptide hormone that suppresses insulin secretion. Its mammalian ortholog, Neuromedin U (NMU), is a peptide that regulates the production and secretion of insulin from pancreatic beta cells. In this study, we used D. melanogaster and human cell culture models to investigate the roles of these insulin regulators in immune signaling. We found that D. melanogaster Lst mutants, which have elevated insulin-like peptide expression, are less susceptible to WNV infection. Increased levels of insulin-like peptides in these flies result in upregulated JAK/STAT activity, leading to protection from infection. Treatment of human cells with the insulin regulator NMU results in increased WNV replication. Further investigation of methods to target Lst in mosquitoes or NMU in mammals can improve vector control methods and may lead to improved therapeutics for human and animal infection.

Wolbachia endosymbionts in Drosophila regulate the resistance to Zika virus infection in a sex dependent manner

Drosophila melanogaster has been used extensively for dissecting the genetic and functional bases of host innate antiviral immunity and virus-induced pathology. Previous studies have shown that the presence of Wolbachia endosymbionts in D. melanogaster confers resistance to infection by certain viral pathogens. Zika virus is an important vector-borne pathogen that has recently expanded its range due to the wide geographical distribution of the mosquito vector. Here, we describe the effect of Wolbachia on the immune response of D. melanogaster adult flies following Zika virus infection. First, we show that the presence of Wolbachia endosymbionts promotes the longevity of uninfected D. melanogaster wild type adults and increases the survival response of flies following Zika virus injection. We find that the latter effect is more pronounced in females rather than in males. Then, we show that the presence of Wolbachia regulates Zika virus replication during Zika virus infection of female flies. In addition, we demonstrate that the antimicrobial peptide-encoding gene Drosocin and the sole Jun N-terminal kinase-specific MAPK phosphatase Puckered are upregulated in female adult flies, whereas the immune and stress response gene TotM is upregulated in male individuals. Finally, we find that the activity of RNA interference and Toll signaling remain unaffected in Zika virus-infected female and male adults containing Wolbachia compared to flies lacking the endosymbionts. Our results reveal that Wolbachia endosymbionts in D. melanogaster affect innate immune signaling activity in a sex-specific manner, which in turn influences host resistance to Zika virus infection. This information contributes to a better understanding of the complex interrelationship between insects, their endosymbiotic bacteria, and viral infection. Interpreting these processes will help us design more effective approaches for controlling insect vectors of infectious disease.

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway contributes to the defense against bacterial infection in the pea aphid

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling is activated by infections of bacteria, fungi, viruses and parasites and mediated cellular and humoral immune responses. In the pea aphid Acyrthosiphon pisum little is known about the function of JAK/STAT signaling in its immune system. In this study, we first showed that expression of genes in the JAK/STAT signaling, including the receptors Domeless1/2, Janus kinase (JAK) and transcriptional factor Stat92E, is up-regulated upon bacteria Escherichia coli and Staphylococcus aureus and fungus Beauveria bassiana infections. After knockdown of expression of these genes by means of dsRNA injection, the aphids harbored more bacteria and suffered more death after infected with E. coli and S. aureus, but showed no significant change after B. bassiana infection. Our study suggests the JAK/STAT signaling contributes to the defense against bacterial infection in the pea aphid.

Evolutionary immunology to explore original antiviral strategies

Over the past 25 years, the field of evolutionary developmental biology (evo-devo) has used genomics and genetics to gain insight on the developmental mechanisms underlying the evolution of morphological diversity of animals. Evo-devo exploits the key insight that conserved toolkits of development (e.g. Hox genes) are used in animals to produce genetic novelties that provide adaptation to a new environment. Like development, immunity is forged by interactions with the environment, namely the microbial world. Yet, when it comes to the study of immune defence mechanisms in invertebrates, interest primarily focuses on evolutionarily conserved molecules also present in humans. Here, focusing on antiviral immunity, we argue that immune genes not conserved in humans represent an unexplored resource for the discovery of new antiviral strategies. We review recent findings on the cGAS-STING pathway and explain how cyclic dinucleotides produced by cGAS-like receptors may be used to investigate the portfolio of antiviral genes in a broad range of species. This will set the stage for evo-immuno approaches, exploiting the investment in antiviral defences made by metazoans over hundreds of millions of years of evolution. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

The circular RNA circATP8B(2) regulates ROS production and antiviral immunity in Drosophila

We identified and validated a collection of circular RNAs (circRNAs) in Drosophila melanogaster. We show that depletion of the pro-viral circRNA circATP8B(2), but not its linear siblings, compromises viral infection both in cultured Drosophila cells and in vivo. In addition, circATP8B(2) is enriched in the fly gut, and gut-specific depletion of circATP8B(2) attenuates viral replication in an oral infection model. Furthermore, circATP8B(2) depletion results in increased levels of reactive oxygen species (ROS) and enhanced expression of dual oxidase (Duox), which produces ROS. Genetic and pharmacological manipulations of circATP8B(2)-depleted flies that reduce ROS levels rescue the viral replication defects elicited by circATP8B(2) depletion. Mechanistically, circATP8B(2) associates with Duox, and circATP8B(2)-Duox interaction is crucial for circATP8B(2)-mediated modulation of Duox activity. In addition, Gαq, a G protein subunit required for optimal Duox activity, acts downstream of circATP8B(2). We conclude that circATP8B(2) regulates antiviral defense by modulating Duox expression and Duox-dependent ROS production.

Molecular Characterization and Expression Analysis of the C-Type Lectin Domain Family 4 Member F in Litopenaeus vannamei against White Spot Syndrome Virus

White spot disease (WSD) outbreaks pose a significant threat to the Pacific white shrimp (Litopenaeus vannamei) farming industry. The causative agent is the white spot syndrome virus (WSSV). There are no effective treatments for WSD so far. Therefore, understanding the resistance mechanisms of L. vannamei against the WSSV is crucial. C-type lectins (CTLs) are important pattern recognition receptors (PRRs) that promote agglutination, phagocytosis, encapsulation, bacteriostasis, and antiviral infections. This study cloned the C-type lectin domain family 4 member F (LvCLEC4F) from L. vannamei. LvCLEC4F contains a 492 bp open reading frame (ORF) encoding a protein of 163 amino acids, including a carbohydrate recognition domain (CRD). Following a challenge with the WSSV, the expression profile of LvCLEC4F was significantly altered. Using RNA interference (RNAi) technology, it was found that LvCLEC4F promotes WSSV replication and affects the expression levels of genes related to the regulation of apoptosis, signaling and cellular stress response, and immune defense. Meanwhile, the hemolymph agglutination phenomenon in vivo was weakened when LvCLEC4F was knocked down. These results indicated that LvCLEC4F may play an important role in the interaction between L. vannamei and WSSV.

Aphid gene expression following polerovirus acquisition is host species dependent

Upon acquisition of persistent circulative viruses such as poleroviruses, the virus particles transcytose through membrane barriers of aphids at the midgut and salivary glands via hemolymph. Such intricate interactions can influence aphid behavior and fitness and induce associated gene expression in viruliferous aphids. Differential gene expression can be evaluated by omics approaches such as transcriptomics. Previously conducted aphid transcriptome studies used only one host species as the source of virus inoculum. Viruses typically have alternate hosts. Hence, it is not clear how alternate hosts infected with the same virus isolate alter gene expression in viruliferous vectors. To address the question, this study conducted a transcriptome analysis of viruliferous aphids that acquired the virus from different host species. A polerovirus, cotton leafroll dwarf virus (CLRDV), which induced gene expression in the cotton aphid, Aphis gossypii Glover, was assessed using four alternate hosts, viz., cotton, hibiscus, okra, and prickly sida. Among a total of 2,942 differentially expressed genes (DEGs), 750, 310, 1,193, and 689 genes were identified in A. gossypii that acquired CLRDV from infected cotton, hibiscus, okra, and prickly sida, respectively, compared with non-viruliferous aphids that developed on non-infected hosts. A higher proportion of aphid genes were overexpressed than underexpressed following CLRDV acquisition from cotton, hibiscus, and prickly sida. In contrast, more aphid genes were underexpressed than overexpressed following CLRDV acquisition from okra plants. Only four common DEGs (heat shock protein, juvenile hormone acid O-methyltransferase, and two unannotated genes) were identified among viruliferous aphids from four alternate hosts. Gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations indicated that the acquisition of CLRDV induced DEGs in aphids associated with virus infection, signal transduction, immune systems, and fitness. However, these induced changes were not consistent across four alternate hosts. These data indicate that alternate hosts could differentially influence gene expression in aphids and presumably aphid behavior and fitness despite being infected with the same virus isolate.

Investigating the Evolution of Drosophila STING-Dependent Antiviral Innate Immunity by Multispecies Comparison of 2'3'-cGAMP Responses

Viruses represent a major threat to all animals, which defend themselves through induction of a large set of virus-stimulated genes that collectively control the infection. In vertebrates, these genes include interferons that play a critical role in the amplification of the response to infection. Virus- and interferon-stimulated genes include restriction factors targeting the different steps of the viral replication cycle, in addition to molecules associated with inflammation and adaptive immunity. Predictably, antiviral genes evolve dynamically in response to viral pressure. As a result, each animal has a unique arsenal of antiviral genes. Here, we exploit the capacity to experimentally activate the evolutionarily conserved stimulator of IFN genes (STING) signaling pathway by injection of the cyclic dinucleotide 2'3'-cyclic guanosine monophosphate-adenosine monophosphate into flies to define the repertoire of STING-regulated genes in 10 Drosophila species, spanning 40 million years of evolution. Our data reveal a set of conserved STING-regulated factors, including STING itself, a cGAS-like-receptor, the restriction factor pastel, and the antiviral protein Vago, but also 2 key components of the antiviral RNA interference pathway, Dicer-2, and Argonaute2. In addition, we identify unknown species- or lineage-specific genes that have not been previously associated with resistance to viruses. Our data provide insight into the core antiviral response in Drosophila flies and pave the way for the characterization of previously unknown antiviral effectors.

Research progress of aphid immunity system: Potential effective target for green pest management

Due to the absence of acquired immunity, insects primarily rely on their innate immune system to resist pathogenic microorganisms and parasitoids in natural habitats. This innate immune system can be classified into cellular immunity and humoral immunity. Cellular immunity is mediated by hemocytes, which perform phagocytosis, aggregation, and encapsulation to fight against invaders, whereas the humoral immunity primarily activates the immune signaling pathways and induces the generation of immune effectors. Existing studies have revealed that the hemipteran aphids lack some crucial immune genes compared to other insect species, indicating the different immune mechanisms in aphids. The current review summarizes the adverse impacts of pathogenic microorganisms and parasitoids on aphids, introduces the cellular and humoral immune systems in insects, and analyzes the differences between aphids and other insect species. Furthermore, our review also discussed the existing prospects and challenges in aphid immunity research, and proposed the potential application of immune genes in green pest management.

cGLRs Join Their Cousins of Pattern Recognition Receptor Family to Regulate Immune Homeostasis

Pattern recognition receptors (PRRs) recognize danger signals such as PAMPs/MAMPs and DAMPs to initiate a protective immune response. TLRs, NLRs, CLRs, and RLRs are well-characterized PRRs of the host immune system. cGLRs have been recently identified as PRRs. In humans, the cGAS/STING signaling pathway is a part of cGLRs. cGAS recognizes cytosolic dsDNA as a PAMP or DAMP to initiate the STING-dependent immune response comprising type 1 IFN release, NF-κB activation, autophagy, and cellular senescence. The present article discusses the emergence of cGLRs as critical PRRs and how they regulate immune responses. We examined the role of cGAS/STING signaling, a well-studied cGLR system, in the activation of the immune system. The following sections discuss the role of cGAS/STING dysregulation in disease and how immune cross-talk with other PRRs maintains immune homeostasis. This understanding will lead to the design of better vaccines and immunotherapeutics for various diseases, including infections, autoimmunity, and cancers.

Molecular characterization, expression analysis and subcellular location of the members of STAT family from spotted seabass (Lateolabrax maculatus)

The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway is a pervasive intracellular signal transduction pathway, involving in biological processes such as cell proliferation, differentiation, apoptosis and immune regulation. In this study, seven STAT genes, STAT1, STAT1-like, STAT2, STAT3, STAT4, STAT5a and STAT5b, were identified and characterized in spotted seabass (Lateolabrax maculatus). Analyses of multiple sequence alignment, genomic organization, phylogeny and conserved synteny were conducted to infer the evolutionary conservation of these genes in the STAT family. The results of the bioinformatics analysis assumed that STAT1 and STAT1-like might be homologous to STAT1a and STAT1b, respectively. Furthermore, the expression of the seven genes were detected in eight tissues of healthy spotted seabass, which revealed that they were expressed in a variety of tissues, mainly in gill, spleen and muscle, and extremely under-expression in liver. The expression of the seven genes in gill, head-kidney, spleen and intestine were significantly induced by lipopolysaccharide (LPS) or Edwardsiella tarda challenge. The expression of most of the LmSTATs were up-regulated, and the highest expression levels at 12 h after LPS stimulation, however, the LmSTATs were down-regulated by E. tarda infection. The results of subcellular localization show that the native LmSTAT1, LmSTAT1-like, LmSTAT2, LmSTAT3 and LmSTAT5a were localized in the cytoplasm, but they were translocated into the nucleus after LPS stimulation. Whereas, LmSTAT4 and LmSTAT5b were translocation into the nucleus whether with LPS stimulation or not. Overall, this is the first study to systematically revealed the localization of STAT members in fish, and indicated that LmSTATs participate in the process of protecting the host from pathogens invasion in the form of entry into nucleus.

Single domain von Willebrand factor type C "cytokines" and the regulation of the stress/immune response in insects

The single domain von Willebrand factor type C (SVWC) appears in small secreted peptides that are arthropod-specific and are produced following environmental stress or pathogen exposure. Most research has focused on proteins with SVWC domain that are induced after virus infection and are hypothesized to function as "cytokines" to regulate the innate immune response. The expansion of SVWC genes in insect species indicates that many other functions remain to be discovered. Research in shrimp has elucidated the adaptability of Vago-like peptides in the innate immune response against bacteria, fungi and viruses after activation by Jak-STAT and/or Toll/Imd pathways in which they can act as pathogen-recognition receptors or cytokine-like signaling molecules. SVWC factors also appear in scorpion venoms and tick saliva, underlining their versatility to acquire new functions. This review discusses the discovery and function of SVWC peptides from insects to crustaceans and chelicerates and reveals the enormous gaps in knowledge that remain to be filled to understand this enigmatic group of secreted peptides.

Methionine can reduce the sublethal risk of Chlorantraniliprole to honeybees (Apis mellifera L.): Based on metabolomics analysis

Bees, essential for pollination in agriculture and global economic growth. However, the great wax moth (Galleria mellonella, GWM), a Lepidopteran insect, poses a substantial threat to bee colonies, contributing to a global decline in bee populations. Chlorantraniliprole (CH) is one of the primary insecticide used to control GWM due to its efficacy and low toxicity to bees. To improve beekeeping safety and reduce the risk of GWM developing resistance to prolonged use of CH, we investigated the potential of combining methionine (MET) which has been found to have insecticidal activity against certain Lepidoptera pests, with chlorantraniliprole for use in the apiculture industry. This study assessed the combined effects of MET and CH on GWM and honeybees by employing the maximum concentration of MET (1 %, w/w), previously reported as safe for honeybees, and the practical concentration of CH (1 mg/kg) for GWM control. The results revealed limited acute lethal toxicity of MET to GWM and honeybees, whereas the combined chronic exposure of MET and CH (MIX) led to significant synergistic lethal effects on GWM mortality. Nevertheless, the protective effect of MET on honeybees exposed to CH was significant under chronic exposure. Potential mechanisms underlying the synergistic actions of MET and CH may stem from MET-induced protection of the "Cysteine and methionine" and the "Glycine, serine, and threonine" metabolism pathways. Furthermore, immune stress mitigation was also observed in honeybee immune-related gene transcripts treated by the combination of MET and CH under both acute and chronic exposure. The effects of MET on CH activity in GWM and honeybees are likely due to metabolic regulation. This study suggests the potential of developing MET as a promising biopesticide or protective agent in the future.

Duox and Jak/Stat signalling influence disease tolerance in Drosophila during Pseudomonas entomophila infection

Disease tolerance describes an infected host's ability to maintain health independently of the ability to clear microbe loads. The Jak/Stat pathway plays a pivotal role in humoral innate immunity by detecting tissue damage and triggering cellular renewal, making it a candidate tolerance mechanism. Here, we find that in Drosophila melanogaster infected with Pseudomonas entomophila disrupting ROS-producing dual oxidase (duox) or the negative regulator of Jak/Stat Socs36E, render male flies less tolerant. Another negative regulator of Jak/Stat, G9a - which has previously been associated with variable tolerance of viral infections - did not affect the rate of mortality with increasing microbe loads compared to flies with functional G9a, suggesting it does not affect tolerance of bacterial infection as in viral infection. Our findings highlight that ROS production and Jak/Stat signalling influence the ability of flies to tolerate bacterial infection sex-specifically and may therefore contribute to sexually dimorphic infection outcomes in Drosophila.

Three STAT isoforms formed by selective splicing are involved in the regulation of anti-lipopolysaccharide factor expression in Macrobrachium nipponense during WSSV infection

White spot syndrome virus (WSSV), a double-stranded DNA virus, is harmful in aquaculture. The signal transducer and activator of transcription (STAT) has been shown to play a role during host infection with the virus, but the exact mechanism by which it acts is unclear. In this study, three STAT isoforms (MnSTAT1, MnSTAT2, and MnSTAT3) were identified in Macrobrachium nipponense. The full-length sequence of MnSTAT1 was 3336 bp, with 2259 bp open reading frame (ORF), encoding a 852 amino acids protein. The full-length sequence of MnSTAT2 was 2538 bp, and the ORF was 2391 bp, encoding 796 amino acids. The full-length sequence of MnSTAT3 sequence was 2618 bp, and the ORF was 2340 bp, encoding 779 amino acids. MnSTAT1-3 is produced by alternative last exon. MnSTAT1-3 all contain a STAT_int, a STAT_alpha, a STAT_bind, and a SH2 structure. MnSTAT1-3 are widely expressed in various tissues tested. The expression levels of MnSTAT1-3 in the intestine of M. nipponense were upregulated at multiple time points following WSSV stimulation. The expression of seven anti-lipopolysaccharide factors (ALFs) was significantly reduced with the knockdown of MnSTATs during WSSV infection. Results showed that MnSTATs regulated the expression of intestinal ALFs and was involved in the innate immunity against WSSV of M. nipponense.

Jamestown Canyon virus is transmissible by Aedes aegypti and is only moderately blocked by Wolbachia co-infection

Jamestown Canyon virus (JCV), a negative-sense arbovirus, is increasingly common in the upper Midwest of the USA. Transmitted by a range of mosquito genera, JCV's primary amplifying host is white-tailed deer. Aedes aegypti is responsible for transmitting various positive-sense viruses globally including dengue (DENV), Zika, chikungunya, and Yellow Fever. Ae. aegypti's distribution, once confined to the tropics, is expanding, in part due to climate change. Wolbachia, an insect endosymbiont, limits the replication of co-infecting viruses inside insects. The release and spread of the symbiont into Ae. aegypti populations have been effective in reducing transmission of DENV to humans, although the mechanism of Wolbachia-mediated viral blocking is still poorly understood. Here we explored JCV infection potential in Ae. aegypti, the nature of the vector's immune response, and interactions with Wolbachia infection. We show that Ae. aegypti is highly competent for JCV, which grows to high loads and rapidly reaches the saliva after an infectious blood meal. The mosquito immune system responds with strong induction of RNAi and JAK/STAT. Neither the direct effect of viral infection nor the energetic investment in immunity appears to affect mosquito longevity. Wolbachia infection blocked JCV only in the early stages of infection. Wolbachia-induced immunity was small compared to that of JCV, suggesting innate immune priming does not likely explain blocking. We propose two models to explain why Wolbachia's blocking of negative-sense viruses like JCV may be less than that of positive-sense viruses, relating to the slowdown of host protein synthesis and the triggering of interferon-like factors like Vago. In conclusion, we highlight the risk for increased human disease with the predicted future overlap of Ae. aegypti and JCV ranges. We suggest that with moderate Wolbachia-mediated blocking and distinct biology, negative-sense viruses represent a fruitful comparator model to other viruses for understanding blocking mechanisms in mosquitoes.

Viruses in Laboratory Drosophila and Their Impact on Host Gene Expression

Drosophila melanogaster has one of the best characterized antiviral immune responses among invertebrates. However, relatively few easily transmitted natural virus isolates are available, and so many Drosophila experiments have been performed using artificial infection routes and artificial host-virus combinations. These may not reflect natural infections, especially for subtle phenotypes such as gene expression. Here, to explore the laboratory virus community and to better understand how natural virus infections induce changes in gene expression, we have analysed seven publicly available D. melanogaster transcriptomic sequencing datasets that were originally sequenced for projects unrelated to virus infection. We have found ten known viruses-including five that have not been experimentally isolated-but no previously unknown viruses. Our analysis of host gene expression revealed that numerous genes were differentially expressed in flies that were naturally infected with a virus. For example, flies infected with nora virus showed patterns of gene expression consistent with intestinal vacuolization and possible host repair via the upd3 JAK/STAT pathway. We also found marked sex differences in virus-induced differential gene expression. Our results show that natural virus infection in laboratory Drosophila does indeed induce detectable changes in gene expression, suggesting that this may form an important background condition for experimental studies in the laboratory.

Anti-Tumor Effect of Turandot Proteins Induced via the JAK/STAT Pathway in the mxc Hematopoietic Tumor Mutant in Drosophila

Several antimicrobial peptides suppress the growth of lymph gland (LG) tumors in Drosophila multi sex comb (mxc) mutant larvae. The activity of another family of polypeptides, called Turandots, is also induced via the JAK/STAT pathway after bacterial infection; however, their influence on Drosophila tumors remains unclear. The JAK/STAT pathway was activated in LG tumors, fat body, and circulating hemocytes of mutant larvae. The mRNA levels of Turandot (Tot) genes increased markedly in the mutant fat body and declined upon silencing Stat92E in the fat body, indicating the involvement of the JAK/STAT pathway. Furthermore, significantly enhanced tumor growth upon a fat-body-specific silencing of the mRNAs demonstrated the antitumor effects of these proteins. The proteins were found to be incorporated into small vesicles in mutant circulating hemocytes (as previously reported for several antimicrobial peptides) but not normal cells. In addition, more hemocytes containing these proteins were found to be associated with tumors. The mutant LGs contained activated effector caspases, and a fat-body-specific silencing of Tots inhibited apoptosis and increased the number of mitotic cells in the LG, thereby suggesting that the proteins inhibited tumor cell proliferation. Thus, Tot proteins possibly exhibit antitumor effects via the induction of apoptosis and inhibition of cell proliferation.

Dietary Supplementation of Aspirin Promotes Drosophila Defense against Viral Infection

Aspirin, also known as acetylsalicylic acid, is widely consumed as a pain reliever and an anti-inflammatory as well as anti-platelet agent. Recently, our studies using the animal model of Drosophila demonstrated that the dietary supplementation of aspirin renovates age-onset intestinal dysfunction and delays organismal aging. Nevertheless, it remains probable that aspirin plays functional roles in other biological activities, for instance antiviral defense reactions. Intriguingly, we observed that the replications of several types of viruses were drastically antagonized in Drosophila macrophage-like S2 cells with the addition of aspirin. Further in vivo experimental approaches illustrate that adult flies consuming aspirin harbor higher resistances to viral infections with respect to flies without aspirin treatment. Mechanistically, aspirin positively contributes to the Drosophila antiviral defense largely through mediating the STING (stimulator of interferon genes) but not the IMD (immune deficiency) signaling pathway. Collectively, our studies uncover a novel biological function of aspirin in modulating Drosophila antiviral immunity and provide theoretical bases for exploring new antiviral treatments in clinical trials.

Genome-wide identification of Coptotermes formosanus immune genes and their potential roles in termite control

In recent years, the use of microbes to control termites has attracted increasing attention. It was found that pathogenic bacteria, nematodes, and fungi effectively control termites under laboratory conditions. However, their effects have not been replicated in the field, and one reason for this is the complex immune defense mechanisms of termites, which are mainly regulated by immune genes. Therefore, altering the expression of immune genes may have a positive influence on the biocontrol efficacy of termites. Coptotermes formosanus Shiraki is one of the most economically important termite pests worldwide. Currently, the large-scale identification of immune genes in C. formosanus is primarily based on cDNA library or transcriptome data rather than at the genomic level. In this study, we identified the immune genes of C. formosanus according to genome-wide analysis. In addition, our transcriptome analysis showed that immune genes were significantly downregulated when C. formosanus was exposed to the fungus Metarhizium anisopliae or nematodes.. Finally, we found that injecting dsRNA to inhibit three immune genes (CfPGRP-SC1, CfSCRB3, and CfHemocytin), which recognize infectious microbes, significantly increased the lethal effect of M. anisopliae on termites. These immune genes show great potential for C. formosanus management based on RNAi. These results also increase the number of known immune genes in C. formosanus which will provide a more comprehensive insight into the molecular basis of immunity in termites.

Single von Willebrand factor C-domain protein confers host defense against white spot syndrome virus by functioning as a pattern recognition receptor in Macrobrachium nipponense

The single von Willebrand factor C-domain proteins (SVWCs), also known as Vago, are primarily found in arthropods. Their expression was induced by nutritional status, bacterial and viral infections. Despite the prominence of SVWCs in antiviral immunity, the detailed molecular mechanisms remain poorly explained. SVWC has been proposed to elicit antiviral activities through its function as an interferon analog. In contrast, herein, we illustrate that an SVWC homolog from Macrobrachium nipponense (MnSVWC) confers host defense against white spot syndrome virus (WSSV) and covert mortality nodavirus (CMNV) as a pattern recognition receptor (PRR). qRT-PCR analyses demonstrated that the expression of MnSVWC was enhanced upon WSSV infection in all detected tissues, including gills, nerve cords, and hemocytes. Coating WSSV with recombinant MnSVWC (rMnSVWC) promoted the phagocytic activity of hemocytes and subsequent clearance of invasive WSSV from the prawn. On the other hand, the knockdown of MnSVWC with RNAi improved the proliferation ability of WSSV and CMNV in the prawn. Analysis of ELISA and Co-immunoprecipitation (Co-IP) showed that rMnSVWC could bind WSSV by interacting with the vesicle proteins VP26 and VP28. Co-IP analysis verified the interaction between MnSVWC and calmodulin, which implies a vesicle protein-SVWC-calmodulin-clathrin-dependent mechanism underlying the hemocyte-mediated phagocytosis against WSSV. Subsequently, MnSVWC was recognized to activate the expression of transcription factor STAT and an interferon-stimulating gene Viperin, illustrating its involvement in modulating humoral immunity via activation of the JAK/STAT pathway after WSSV infection. These findings indicate that MnSVWC could bind to WSSV as a PRR and participate in the promotion of hemocyte-mediated phagocytosis and the activation of the JAK/STAT pathway in prawns.

Influence of RVFV Infection on Olfactory Perception and Behavior in Drosophila melanogaster

In blood-feeding dipterans, olfaction plays a role in finding hosts and, hence, in spreading pathogens. Several pathogens are known to alter olfactory responses and behavior in vectors. As a mosquito-borne pathogen, Rift Valley Fever Virus (RVFV) can affect humans and cause great losses in livestock. We test the influence of RVFV infection on sensory perception, olfactory choice behavior and activity on a non-biting insect, Drosophila melanogaster, using electroantennograms (EAG), Y-maze, and locomotor activity monitor. Flies were injected with RVFV MP12 strain. Replication of RVFV and its persistence for at least seven days was confirmed by quantitative reverse transcription-PCR (RT-qPCR). One day post injection, infected flies showed weaker EAG responses towards 1-hexanol, vinegar, and ethyl acetate. In the Y-maze, infected flies showed a significantly lower response for 1-hexanol compared to uninfected flies. At days six or seven post infection, no significant difference between infected and control flies could be found in EAG or Y-maze anymore. Activity of infected flies was reduced at both time points. We found an upregulation of the immune-response gene, nitric oxide synthase, in infected flies. An infection with RVFV is able to transiently reduce olfactory perception and attraction towards food-related odors in Drosophila, while effects on activity and immune effector gene expression persist. A similar effect in blood-feeding insects could affect vector competence in RVFV transmitting dipterans.

A Brief History of the Discovery of RNA-Mediated Antiviral Immune Defenses in Vector Mosquitos

Arthropod-borne viruses (arboviruses) persist in a natural cycle that includes infections of humans or other vertebrates and transmission between vertebrates by infected arthropods, most commonly mosquitos. Arboviruses can cause serious, sometimes fatal diseases in humans and other vertebrates but cause little pathology in their mosquito vectors. Knowledge of the interactions between mosquito vectors and the arboviruses that they transmit is an important facet of developing schemes to control transmission. Mosquito innate immune responses to virus infection modulate virus replication in the vector, and understanding the components and mechanisms of the immune response could lead to improved methods for interrupting the transmission cycle. The most important aspect of mosquito antiviral defense is the exogenous small interfering RNA (exo-siRNA) pathway, one arm of the RNA interference (RNAi) silencing response. Our research as well as that of many other groups over the past 25 years to define this pathway are reviewed here. A more recently recognized but less well-understood RNA-mediated mosquito defense against arbovirus infections, the PIWI-interacting RNA (piRNA) pathway, is also described.

Systematic Characterization and Regulatory Role of lncRNAs in Asian Honey Bees Responding to Microsporidian Infestation

Long noncoding RNAs (lncRNAs) are pivotal regulators in gene expression and diverse biological processes, such as immune defense and host-pathogen interactions. However, little is known about the roles of lncRNAs in the response of the Asian honey bee (Apis cerana) to microsporidian infestation. Based on our previously obtained high-quality transcriptome datasets from the midgut tissues of Apis cerana cerana workers at 7 days post inoculation (dpi) and 10 dpi with Nosema ceranae (AcT7 and AcT10 groups) and the corresponding un-inoculated midgut tissues (AcCK7 and AcCK10 groups), the transcriptome-wide identification and structural characterization of lncRNAs were conducted, and the differential expression pattern of lncRNAs was then analyzed, followed by investigation of the regulatory roles of differentially expressed lncRNAs (DElncRNAs) in host response. Here, 2365, 2322, 2487, and 1986 lncRNAs were, respectively, identified in the AcCK7, AcT7, AcCK7, and AcT10 groups. After removing redundant ones, a total of 3496 A. c. cerana lncRNAs were identified, which shared similar structural characteristics with those discovered in other animals and plants, such as shorter exons and introns than mRNAs. Additionally, 79 and 73 DElncRNAs were screened from the workers' midguts at 7 dpi and 10 dpi, respectively, indicating the alteration of the overall expression pattern of lncRNAs in host midguts after N. ceranae infestation. These DElncRNAs could, respectively, regulate 87 and 73 upstream and downstream genes, involving a suite of functional terms and pathways, such as metabolic process and Hippo signaling pathway. Additionally, 235 and 209 genes co-expressed with DElncRNAs were found to enrich in 29 and 27 terms, as well as 112 and 123 pathways, such as ABC transporters and the cAMP signaling pathway. Further, it was detected that 79 (73) DElncRNAs in the host midguts at 7 (10) dpi could target 321 (313) DEmiRNAs and further target 3631 (3130) DEmRNAs. TCONS_00024312 and XR_001765805.1 were potential precursors for ame-miR-315 and ame-miR-927, while TCONS_00006120 was the putative precursor for both ame-miR-87-1 and ame-miR-87-2. These results together suggested that DElncRNAs are likely to play regulatory roles in the host response to N. ceranae infestation through the regulation of neighboring genes via a cis-acting effect, modulation of co-expressed mRNAs via trans-acting effect, and control of downstream target genes' expression via competing endogenous RNA networks. Our findings provide a basis for disclosing the mechanism underlying DElncRNA-mediated host N. ceranae response and a new perspective into the interaction between A. c. cerana and N. ceranae.

The JAK-STAT pathway promotes persistent viral infection by activating apoptosis in insect vectors

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway is an evolutionarily conserved signaling pathway that can regulate various biological processes. However, the role of JAK-STAT pathway in the persistent viral infection in insect vectors has rarely been investigated. Here, using a system that comprised two different plant viruses, Rice stripe virus (RSV) and Rice black-streaked dwarf virus (RBSDV), as well as their insect vector small brown planthopper, we elucidated the regulatory mechanism of JAK-STAT pathway in persistent viral infection. Both RSV and RBSDV infection activated the JAK-STAT pathway and promoted the accumulation of suppressor of cytokine signaling 5 (SOCS5), an E3 ubiquitin ligase regulated by the transcription factor STAT5B. Interestingly, the virus-induced SOCS5 directly interacted with the anti-apoptotic B-cell lymphoma-2 (BCL2) to accelerate the BCL2 degradation through the 26S proteasome pathway. As a result, the activation of apoptosis facilitated persistent viral infection in their vector. Furthermore, STAT5B activation promoted virus amplification, whereas STAT5B suppression inhibited apoptosis and reduced virus accumulation. In summary, our results reveal that virus-induced JAK-STAT pathway regulates apoptosis to promote viral infection, and uncover a new regulatory mechanism of the JAK-STAT pathway in the persistent plant virus transmission by arthropod vectors.

Impact of different diets on the survival, pupation, and adult emergence of Culex pipiens biotype molestus larvae, and infectability with the insect-specific Culex Y virus

The current rapidly advancing climate change will affect the transmission of arthropod-borne viruses (arboviruses), mainly through changes in vector populations. Mosquitos of the Culex pipiens complex play a particularly prominent role in virus transmission in central Europe. Factors that contribute to the vector population density and the ability of those vectors to transmit viral pathogens (vector competence) can include nutrition during the larval stages. To test the influence of larval diet on larval survival and adult emergence, as well as vector competence, several diets varying in their nutritional composition were compared using a newly established assay. We tested the effects of 17 diets or diet combinations on the fitness of third-instar larvae of Culex pipiens biotype molestus. Larval survival rates at day 7 ranged from 43.33% to 94.44%. We then selected 3 of the 17 diets (Tetra Pleco, as the routine feed; JBL NovoTab, as the significantly inferior feed; and KG, as the significantly superior feed) and tested the effect of these diets, in combination with Culex Y virus infection, on larval survival rate. All Culex Y virus-infected larvae showed significantly lower larval survival, as well as low pupation and adult emergence rates. However, none of the tested diets in our study had a significant impact on larval survival in combination with viral infection. Furthermore, we were able to correlate several water quality parameters, such as phosphate, nitrate, and ammonium concentration, electrical conductivity, and low O2 saturations, with reduced larval survival. Thus, we were able to demonstrate that Culex Y virus could be a suitable agent to reduce mosquito population density by reducing larval density, pupation rate, and adult emergence rate. When combined with certain water quality parameters, these effects can be further enhanced, leading to a reduced mosquito population density, and reduce the cycle of transmission. Furthermore, we demonstrate, for the first time, the infection of larvae of the mosquito Culex pipiens biotype molestus with a viral pathogen.

Intraspecific genetic variation in host vigour, viral load and disease tolerance during Drosophila C virus infection

Genetic variation for resistance and disease tolerance has been described in a range of species. In Drosophila melanogaster, genetic variation in mortality following systemic Drosophila C virus (DCV) infection is driven by large-effect polymorphisms in the restriction factor pastrel (pst). However, it is unclear if pst contributes to disease tolerance. We investigated systemic DCV challenges spanning nine orders of magnitude, in males and females of 10 Drosophila Genetic Reference Panel lines carrying either a susceptible (S) or resistant (R) pst allele. We find among-line variation in fly survival, viral load and disease tolerance measured both as the ability to maintain survival (mortality tolerance) and reproduction (fecundity tolerance). We further uncover novel effects of pst on host vigour, as flies carrying the R allele exhibited higher survival and fecundity even in the absence of infection. Finally, we found significant genetic variation in the expression of the JAK-STAT ligand upd3 and the epigenetic regulator of JAK-STAT G9a. However, while G9a has been previously shown to mediate tolerance of DCV infection, we found no correlation between the expression of either upd3 or G9a on fly tolerance or resistance. Our work highlights the importance of both resistance and tolerance in viral defence.

Drosophila Ectoderm-expressed 4 modulates JAK/STAT pathway and protects flies against Drosophila C virus infection

Sterile alpha and HEAT/Armadillo motif-containing protein (SARM) is conserved in evolution and negatively regulates TRIF-dependent Toll signaling in mammals. The SARM protein from Litopenaeus vannamei and its Drosophila orthologue Ectoderm-expressed (Ect4) are also involved in immune defense against pathogen infection. However, the functional mechanism of the protective effect remains unclear. In this study, we show that Ect4 is essential for the viral load in flies after a Drosophila C virus (DCV) infection. Viral load is increased in Ect4 mutants resulting in higher mortality rates than wild-type. Overexpression of Ect4 leads to a suppression of virus replication and thus improves the survival rate of the animals. Ect4 is required for the viral induction of STAT-responsive genes, TotA and TotM. Furthermore, Ect4 interacts with Stat92E, affecting the tyrosine phosphorylation and nuclear translocation of Stat92E in S2 cells. Altogether, our study identifies the adaptor protein Ect4 of the Toll pathway contributes to resistance to viral infection and regulates JAK/STAT signaling pathway.

Drosophila caspases as guardians of host-microbe interactions

An intact cell death machinery is not only crucial for successful embryonic development and tissue homeostasis, but participates also in the defence against pathogens and contributes to a balanced immune response. Centrally involved in the regulation of both cell death and inflammatory immune responses is the evolutionarily conserved family of cysteine proteases named caspases. The Drosophila melanogaster genome encodes for seven caspases, several of which display dual functions, participating in apoptotic signalling and beyond. Among the Drosophila caspases, the caspase-8 homologue Dredd has a well-characterised role in inflammatory signalling activated by bacterial infections, and functions as a driver of NF-κB-mediated immune responses. Regarding the other Drosophila caspases, studies focusing on tissue-specific immune signalling and host-microbe interactions have recently revealed immunoregulatory functions of the initiator caspase Dronc and the effector caspase Drice. The aim of this review is to give an overview of the signalling cascades involved in the Drosophila humoral innate immune response against pathogens and of their caspase-mediated regulation. Furthermore, the apoptotic role of caspases during antibacterial and antiviral immune activation will be discussed.

Origins and diversification of animal innate immune responses against viral infections

Immune systems are of pivotal importance to any living organism on Earth, as they protect the organism against deleterious effects of viral infections. Though the current knowledge about these systems is still biased towards the immune response in vertebrates, some studies have focused on the identification and characterization of components of invertebrate antiviral immune systems. Two classic model organisms, the insect Drosophila melanogaster and the nematode Caenorhabditis elegans, were instrumental in the discovery of several important components of the innate immune system, such as the Toll-like receptors and the RNA interference pathway. However, these two model organisms provide only a limited view of the evolutionary history of the immune system, as they both are ecdysozoan protostomes. Recent functional studies in non-classic models such as unicellular holozoans (for example, choanoflagellates), lophotrochozoans (for example, oysters) and cnidarians (for example, sea anemones) have added crucial information for understanding the evolution of antiviral systems, as they revealed unexpected ancestral complexity. This Review aims to summarize this information and present the ancestral nature of the antiviral immune response in animals. We also discuss lineage-specific adaptations and future perspectives for the comparative study of the innate immune system that are essential for understanding its evolution.

Factors Affecting Arbovirus Midgut Escape in Mosquitoes

Arboviral diseases spread by mosquitoes cause significant morbidity and mortality throughout much of the world. The treatment and prevention of these diseases through medication and vaccination is often limited, which makes controlling arboviruses at the level of the vector ideal. One way to prevent the spread of an arbovirus would be to stop its vector from developing a disseminated infection, which is required for the virus to make its way to the saliva of the mosquito to be potentially transmitted to a new host. The midgut of the mosquito provides one such opportunity to stop an arbovirus in its tracks. It has been known for many years that in certain arbovirus-vector combinations, or under certain circumstances, an arbovirus can infect and replicate in the midgut but is unable to escape from the tissue to cause disseminated infection. This situation is known as a midgut escape barrier. If we better understand why this barrier occurs, it might aid in the development of more informed control strategies. In this review, we discuss how the midgut escape barrier contributes to virus-vector specificity and possible mechanisms that may allow this barrier to be overcome in successful virus-vector combinations. We also discuss several of the known factors that either increase or decrease the likelihood of midgut escape.

Targeting Nup358/RanBP2 by a viral protein disrupts stress granule formation

Viruses have evolved mechanisms to modulate cellular pathways to facilitate infection. One such pathway is the formation of stress granules (SG), which are ribonucleoprotein complexes that assemble during translation inhibition following cellular stress. Inhibition of SG assembly has been observed under numerous virus infections across species, suggesting a conserved fundamental viral strategy. However, the significance of SG modulation during virus infection is not fully understood. The 1A protein encoded by the model dicistrovirus, Cricket paralysis virus (CrPV), is a multifunctional protein that can bind to and degrade Ago-2 in an E3 ubiquitin ligase-dependent manner to block the antiviral RNA interference pathway and inhibit SG formation. Moreover, the R146 residue of 1A is necessary for SG inhibition and CrPV infection in both Drosophila S2 cells and adult flies. Here, we uncoupled CrPV-1A's functions and provide insight into its underlying mechanism for SG inhibition. CrPV-1A mediated inhibition of SGs requires the E3 ubiquitin-ligase binding domain and the R146 residue, but not the Ago-2 binding domain. Wild-type but not mutant CrPV-1A R146A localizes to the nuclear membrane which correlates with nuclear enrichment of poly(A)+ RNA. Transcriptome changes in CrPV-infected cells are dependent on the R146 residue. Finally, Nup358/RanBP2 is targeted and degraded in CrPV-infected cells in an R146-dependent manner and the depletion of Nup358 blocks SG formation. We propose that CrPV utilizes a multiprong strategy whereby the CrPV-1A protein interferes with a nuclear event that contributes to SG inhibition in order to promote infection.

Drosophila as an Animal Model for Testing Plant-Based Immunomodulators

Allopathic medicines play a key role in the prevention and treatment of diseases. However, long-term consumption of these medicines may cause serious undesirable effects that harm human health. Plant-based medicines have emerged as alternatives to allopathic medicines because of their rare side effects. They contain several compounds that have the potential to improve health and treat diseases in humans, including their function as immunomodulators to treat immune-related diseases. Thus, the discovery of potent and safe immunomodulators from plants is gaining considerable research interest. Recently, Drosophila has gained prominence as a model organism in evaluating the efficacy of plant and plant-derived substances. Drosophila melanogaster "fruit fly" is a well-known, high-throughput model organism that has been used to study different biological aspects of development and diseases for more than 110 years. Most developmental and cell signaling pathways and 75% of human disease-related genes are conserved between humans and Drosophila. Using Drosophila, one can easily examine the pharmacological effects of plants/plant-derived components by employing a variety of tests in flies, such as survival, anti-inflammatory, antioxidant, and cell death tests. This review focused on D. melanogaster's potential for identifying immunomodulatory features associated with plants/plant-derived components.

Characterization of Cross-Species Transmission of Drosophila melanogaster Nora Virus

Drosophila melanogaster Nora virus (DmNV) is a novel picorna-like virus first characterized in 2006. Since then, Nora virus has been detected in several non-Drosophila species, including insects in the Orders Hymenoptera, Lepidoptera, Coleoptera, and Orthoptera. The objective of this study was to determine if DmNV could infect individuals of other species of invertebrates besides D. melanogaster. The presence of DmNV in native invertebrates and commercially available stocks was determined. Laboratory-reared D. yakuba, D. mercatorum, Gryllodes sigillatus, Tenebrio molitor, Galleria mellonella, and Musca domestica were intentionally infected with DmNV. In addition, native invertebrates were collected and D. melanogaster stocks were purchased and screened for DmNV presence using reverse transcription-polymerase chain reaction (RT-PCR) before being intentionally infected for study. All Drosophila species and other invertebrates, except M. domestica, that were intentionally infected with DmNV ended up scoring positive for the virus via RT-PCR. DmNV infection was also detected in three native invertebrates (Spilosoma virginica, Diplopoda, and Odontotaenius disjunctus) and all commercially available stocks tested. These findings suggest that DmNV readily infects individuals of other species of invertebrates, while also appearing to be an endemic virus in both wild and laboratory D. melanogaster populations. The detection of DmNV in commercially available stocks presents a cautionary message for scientists using these stocks in studies of virology and immunology.

Cotton leaf curl Multan virus differentially regulates innate antiviral immunity of whitefly (Bemisia tabaci) vector to promote cryptic species-dependent virus acquisition

Begomoviruses represent the largest group of economically important, highly pathogenic, DNA plant viruses that contribute a substantial amount of global crop disease burden. The exclusive transmission of begomoviruses by whiteflies (Bemisia tabaci) requires them to interact and efficiently manipulate host responses at physiological, biological and molecular scales. However, the molecular mechanisms underlying complex begomovirus-whitefly interactions that consequently substantiate efficient virus transmission largely remain unknown. Previously, we found that whitefly Asia II 7 cryptic species can efficiently transmit cotton leaf curl Multan virus (CLCuMuV) while MEAM1 cryptic species is a poor carrier and incompetent vector of CLCuMuV. To investigate the potential mechanism/s that facilitate the higher acquisition of CLCuMuV by its whitefly vector (Asia II 7) and to identify novel whitefly proteins that putatively interact with CLCuMuV-AV1 (coat protein), we employed yeast two-hybrid system, bioinformatics, bimolecular fluorescence complementation, RNA interference, RT-qPCR and bioassays. We identified a total of 21 Asia II 7 proteins putatively interacting with CLCuMuV-AV1. Further analyses by molecular docking, Y2H and BiFC experiments validated the interaction between a whitefly innate immunity-related protein (BTB/POZ) and viral AV1 (coat protein). Gene transcription analysis showed that the viral infection significantly suppressed the transcription of BTB/POZ and enhanced the accumulation of CLCuMuV in Asia II 7, but not in MEAM1 cryptic species. In contrast to MEAM1, the targeted knock-down of BTB/POZ substantially reduced the ability of Asia II 7 to acquire and accumulate CLCuMuV. Additionally, antiviral immune signaling pathways (Toll, Imd, Jnk and Jak/STAT) were significantly suppressed following viral infection of Asia II 7 whiteflies. Taken together, the begomovirus CLCuMuV potentiates efficient virus accumulation in its vector B. tabaci Asia II 7 by targeting and suppressing the transcription of an innate immunity-related BTB/POZ gene and other antiviral immune responses in a cryptic species-specific manner.

A balance between vector survival and virus transmission is achieved through JAK/STAT signaling inhibition by a plant virus

Viruses pose a great threat to animal and plant health worldwide, with many being dependent on insect vectors for transmission between hosts. While the virus-host arms race has been well established, how viruses and insect vectors adapt to each other remains poorly understood. Begomoviruses comprise the largest genus of plant-infecting DNA viruses and are exclusively transmitted by the whitefly Bemisia tabaci. Here, we show that the vector Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway plays an important role in mediating the adaptation between the begomovirus tomato yellow leaf curl virus (TYLCV) and whiteflies. We found that the JAK/STAT pathway in B. tabaci functions as an antiviral mechanism against TYLCV infection in whiteflies as evidenced by the increase in viral DNA and coat protein (CP) levels after inhibiting JAK/STAT signaling. Two STAT-activated effector genes, BtCD109-2 and BtCD109-3, mediate this anti-TYLCV activity. To counteract this vector immunity, TYLCV has evolved strategies that impair the whitefly JAK/STAT pathway. Infection of TYLCV is associated with a reduction of JAK/STAT pathway activity in whiteflies. Moreover, TYLCV CP binds to STAT and blocks its nuclear translocation, thus, abrogating the STAT-dependent transactivation of target genes. We further show that inhibition of the whitefly JAK/STAT pathway facilitates TYLCV transmission but reduces whitefly survival and fecundity, indicating that this JAK/STAT-dependent TYLCV-whitefly interaction plays an important role in keeping a balance between whitefly fitness and TYLCV transmission. This study reveals a mechanism of plant virus-insect vector coadaptation in relation to vector survival and virus transmission.

Immunostimulation of shrimp through oral administration of silkworm pupae expressing VP15 against WSSV

White spot syndrome virus (WSSV) is one of the most concerning pathogens in penaeid shrimp and can cause severe loss in shrimp aquaculture worldwide. Among the WSSV structural proteins, VP15, a DNA-binding protein located in the WSSV nucleocapsid, is an antiviral protein candidate to protect kuruma shrimp (Marsupenaeus japonicus) from WSSV infection. We identified that the truncated VP15, VP15_(26-57), is responsible for the protective effect against the WSSV. This study attempts to develop an immunizing agent against WSSV using silkworm pupa as a delivery vector through oral administration. The VP15, VP15_(26-57), and SR11 peptide derived from VP15_(26-57) were expressed in silkworm pupae. Oral administration of feed mixed with the powdered pupae that expressed VP15-derived constructs enhanced the survivability of kuruma shrimp with an overall relative percent survival (RPS) higher than 70%. There is no death for the group receiving pupa/VP15_(26-57), and the RPS is 100%. In addition, we also investigated the relative mRNA expression levels of immune-related genes by qPCR at different time points. Our results indicate that the oral administration of pupa/VP15-derived products could provide a high protective effect against WSSV and be a practical approach for controlling WSSV in aquaculture.

Drosophila as a Model for Human Viral Neuroinfections

The study of human neurological infection faces many technical and ethical challenges. While not as common as mammalian models, the use of Drosophila (fruit fly) in the investigation of virus–host dynamics is a powerful research tool. In this review, we focus on the benefits and caveats of using Drosophila as a model for neurological infections and neuroimmunity. Through the examination of in vitro, in vivo and transgenic systems, we highlight select examples to illustrate the use of flies for the study of exogenous and endogenous viruses associated with neurological disease. In each case, phenotypes in Drosophila are compared to those in human conditions. In addition, we discuss antiviral drug screening in flies and how investigating virus–host interactions may lead to novel antiviral drug targets. Together, we highlight standardized and reproducible readouts of fly behaviour, motor function and neurodegeneration that permit an accurate assessment of neurological outcomes for the study of viral infection in fly models. Adoption of Drosophila as a valuable model system for neurological infections has and will continue to guide the discovery of many novel virus–host interactions.

A dRASSF-STRIPAK-Imd-JAK/STAT axis controls antiviral immune response in Drosophila

Host antiviral immunity suffers strong pressure from rapidly evolving viruses. Identifying host antiviral immune mechanisms has profound implications for developing antiviral strategies. Here, we uncover an essential role for the tumor suppressor Ras-association domain family (RASSF) in Drosophila antiviral response. Loss of dRassf in fat body leads to increased vulnerability to viral infection and impaired Imd pathway activation accompanied by detrimental JAK/STAT signaling overactivation. Mechanistically, dRASSF protects TAK1, a key kinase of Imd pathway, from inhibition by the STRIPAK PP2A phosphatase complex. Activated Imd signaling then employs the effector Relish to interfere with the dimerization of JAK/STAT transmembrane receptor Domeless, therefore preventing excessive JAK/STAT signaling. Moreover, we find that RASSF and STRIPAK PP2A complex are also involved in antiviral response in human cell lines. Our study identifies an important role for RASSF in antiviral immunity and elucidates a dRASSF-STRIPAK-Imd-JAK/STAT signaling axis that ensures proper antiviral responses in Drosophila.

Meta-Analysis of Immune Induced Gene Expression Changes in Diverse Drosophila melanogaster Innate Immune Responses

Simple Summary

Organisms can be infected by a wide range of pathogens, including bacteria, viruses, and parasites. Following infection, the host mounts an immune response to attempt to eliminate the pathogen. These responses are often specific to the type of pathogen and mediated by the expression of specialized genes. We have characterized the expression changes induced in host Drosophila fruit flies following infection by multiple types of pathogens, and identified a small number of genes that show expression changes in each infection. This includes genes that are known to be involved in pathogen resistance, and others that have not been previously studied as immune response genes. These findings provide new insight into transcriptional changes that accompany Drosophila immunity. They may suggest possible roles for the differentially expressed genes in innate immune responses to diverse classes of pathogens, and serve to identify candidate genes for further empirical study of these processes.

Abstract

Organisms are commonly infected by a diverse array of pathogens and mount functionally distinct responses to each of these varied immune challenges. Host immune responses are characterized by the induction of gene expression, however, the extent to which expression changes are shared among responses to distinct pathogens is largely unknown. To examine this, we performed meta-analysis of gene expression data collected from Drosophila melanogaster following infection with a wide array of pathogens. We identified 62 genes that are significantly induced by infection. While many of these infection-induced genes encode known immune response factors, we also identified 21 genes that have not been previously associated with host immunity. Examination of the upstream flanking sequences of the infection-induced genes lead to the identification of two conserved enhancer sites. These sites correspond to conserved binding sites for GATA and nuclear factor κB (NFκB) family transcription factors and are associated with higher levels of transcript induction. We further identified 31 genes with predicted functions in metabolism and organismal development that are significantly downregulated following infection by diverse pathogens. Our study identifies conserved gene expression changes in Drosophila melanogaster following infection with varied pathogens, and transcription factor families that may regulate this immune induction.

The antiviral role of NF-κB-mediated immune responses and their antagonism by viruses in insects

The antiviral role of innate immune responses mediated by the NF-κB family of transcription factors is well established in vertebrates but was for a long time less clear in insects. Insects encode two canonical NF-κB pathways, the Toll and Imd ('immunodeficiency') pathways, which are best characterised for their role in antibacterial and antifungal defence. An increasing body of evidence has also implicated NF-κB-mediated innate immunity in antiviral responses against some, but not all, viruses. Specific pattern recognition receptors (PRRs) and molecular events leading to NF-κB activation by viral pathogen-associated molecular patterns (PAMPs) have been elucidated for a number of viruses and insect species. Particularly interesting are recent findings indicating that the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway detects viral RNA to activate NF-κB-regulated gene expression. We summarise the literature on virus-NF-κB pathway interactions across the class Insecta, with a focus on the dipterans Drosophila melanogaster and Aedes aegypti. We discuss potential reasons for differences observed between different virus-host combinations, and highlight similarities and differences between cGAS-STING signalling in insects versus vertebrates. Finally, we summarise the increasing number of known molecular mechanisms by which viruses antagonise NF-κB responses, which suggest that NF-κB-mediated immunity exerts strong evolutionary pressures on viruses. These developments in our understanding of insect antiviral immunity have relevance to the large number of insect species that impact on humans through their transmission of human, livestock and plant diseases, exploitation as biotechnology platforms, and role as parasites, pollinators, livestock and pests.