The gene expression profile of resistant and susceptible Bombyx mori strains reveals cypovirus-associated variations in host gene transcript levels

BmHSP19.9 targeting P6.9 and VLF-1 to mediate the formation of defective progeny viruses in the silkworm antiviral variety 871C

The 871C silkworm strain exhibits a high level of resistance to Bombyx mori nucleopolyhedrovirus (BmNPV), making it a valuable variety for the sericulture industry. Understanding the underlying mechanism of its resistance holds great biological significance and economic value in addressing viral disease risks in sericulture. Initially, we infected the resistant strain 871C and its control strain 871 with BmNPV and conducted secondary infection experiments using the progeny occlusion bodies (OBs). As a result, a significant decrease in pathogenicity was observed. Electron microscopy analysis revealed that 871C produces progeny virions with defective DNA packaging, reducing virulence following BmNPV infection. Blood proteomic identification of the silkworm variety 871C and control 871 after BmNPV infection demonstrated the crucial role of the viral proteins P6.9 and VLF-1 in the production of defective viruses by impeding the proper encapsulation of viral DNA. Additionally, we discovered that BmHSP19.9 interacts with P6.9 and VLF-1 and that its expression is significantly upregulated after BmNPV infection. BmHSP19.9 exhibits strong antiviral activity, in part by preventing the entry of the proteins P6.9 and VLF-1 into the nucleus, thereby hindering viral nucleocapsid and viral DNA assembly. Our findings indicate that the antiviral silkworm strain 871C inhibits BmNPV proliferation by upregulating Bmhsp19.9 and impeding the nuclear localization of the viral proteins P6.9 and VLF-1, leading to the production of defective viral particles. This study offers a comprehensive analysis of the antiviral mechanism in silkworms from a viral perspective, providing a crucial theoretical foundation for future antiviral research and the breeding of resistant silkworm strains.

The mechanisms and factors that induce trained immunity in arthropods and mollusks

Besides dividing the organism's immune system into adaptive and innate immunity, it has long been thought that only adaptive immunity can establish immune memory. However, many studies have shown that innate immunity can also build immunological memory through epigenetic reprogramming and modifications to resist pathogens' reinfection, known as trained immunity. This paper reviews the role of mitochondrial metabolism and epigenetic modifications and describes the molecular foundation in the trained immunity of arthropods and mollusks. Mitochondrial metabolism and epigenetic modifications complement each other and play a key role in trained immunity.

Identification of Key Genes Involved in Resistance to Early Stage of BmNPV Infection in Silkworms

Bombyx mori nucleopolyhedrovirus (BmNPV) is one of the most serious pathogens restricting the sustainable development of the sericulture industry. Currently, there is no effective treatment for BmNPV infection in silkworms, and the mechanism underlying BmNPV resistance in silkworms is also not clear. In this study, comparative transcriptome analyses were carried out in midguts of two silkworm varieties, namely BaiyuN, which is a resistance variety, and Baiyu, which is a susceptible variety, at five different time points (i.e., 0, 1, 3, 6, and 9 h) post-BmNPV infection to detect the early-stage transcriptional changes in these silkworms. In total, 1911 and 1577 differentially expressed genes (DEGs) were identified in the Baiyu and BaiyuN varieties, respectively, involving a total of 48 metabolic pathways. Of these pathways, eight were shared by the Baiyu and BaiyuN varieties in response to BmNPV infection. Notably, four genes (i.e., BGIBMGA08815, BGIBMGA003935, BGIBMGA003571, BGIBMGA010059) were upregulated in the Baiyu variety while downregulated in the BaiyuN variety. The inhibited expression of these four genes in the resistant variety highlighted their potential roles in the resistance of early-stage viral replication. Thus, our study provided a new avenue for the further study of the mechanism underlying BmNPV infection in silkworms and the potential treatment of BmNPV infection.

BmCPV-Derived Circular DNA vcDNA-S7 Mediated by Bombyx mori Reverse Transcriptase (RT) Regulates BmCPV Infection

Circular DNAs derived from single-stranded RNA viruses play important roles in counteracting viral infection. However, whether double-stranded RNA viruses generate functional circular DNAs is still unknown. Using circDNA sequencing, divergent PCR, DNA in situ hybridization and rolling circular amplification, we presently confirmed that in silkworm, Bombyx mori cytoplasmic polyhedrosis virus (BmCPV), a double-stranded RNA virus belonging to cypovirus, is prone to produce a BmCPV-derived circular DNA termed as vcDNA-S7. We have also found that vcDNA-S7 formation is mediated by endogenous reverse transcriptase (RT), and the proliferation of BmCPV can be inhibited by vcDNA-S7 in vitro and in vivo. Moreover, we have discovered that the silkworm RNAi immune pathway is activated by vcDNA-S7, while viral small interfering RNAs (vsiRNAs) derived from transcribed RNA by vcDNA-S7 can be detected by small RNA deep sequencing. These results suggest that BmCPV-derived vcDNA-S7, mediated by RT, can serve as a template for the biogenesis of antiviral siRNAs, which may lead to the repression of BmCPV infection. To our knowledge, this is the first demonstration that a circular DNA, produced by double stranded RNA viruses, is capable of regulating virus infection.

Bombyx mori cypovirus (BmCPV) induces PINK1-Parkin mediated mitophagy via interaction of VP4 with host Tom40

The mechanism by which infection by Bombyx mori cytoplasmic nucleopolyhedrosis virus (BmCPV) causes autophagy has not been studied in detail. Herein we have observed by electron microscopy that infection with BmCPV causes autophagosome and mitochondrial structure damage in Bombyx mori midgut. In BmN cells infected with BmCPV and expressing eGFP-LC3, fluorescence spots and LC3-II levels increased, suggesting that BmCPV infection causes autophagy. Autophagy inducer rapamycin (Rap) and autophagy inhibitor 3-methyladenine (3-MA) were used to monitor the effects of mitophagy on BmCPV proliferation. It was found BmCPV proliferation to be promoted by mitophagy. Transient transfection experiments in cultured BmN cells showed that mitophagy can be triggered by expression of BmCPV structural protein VP4. Moreover, VP4 caused upregulation of p-Drp1, PINK1 and Parkin proteins in the mitophagy pathway and downregulation of mitochondrial membrane protein Tom20. Furthermore, interaction between VP4 with Tom40 was confirmed by Co-IP, western blot and colocalization experiment, and overexpression of Tom40 reduce the level of mitochondrial autophagy induced by VP4. These results suggested that VP4 induced PINK1-Parkin-mediated mitophagy interacting with Tom40. These findings deepen our understanding of the interaction between BmCPV and silkworm and also provide a molecular target for screening anti-BmCPV drugs.

Transcriptional responses of Daphnis nerii larval midgut to oral infection by Daphnis nerii cypovirus-23

BACKGROUND

Daphnis nerii cypovirus-23 (DnCPV-23) is a new type of cypovirus and has a lethal effect on the oleander hawk moth, Daphnis nerii which feeds on leave of Oleander and Catharanthus et al. After DnCPV-23 infection, the change of Daphnis nerii responses has not been reported.

METHODS

To better understand the pathogenic mechanism of DnCPV-23 infection, 3rd-instar Daphnis nerii larvae were orally infected with DnCPV-23 occlusion bodies and the transcriptional responses of the Daphnis nerii midgut were analyzed 72 h post-infection using RNA-seq.

RESULTS

The results showed that 1979 differentially expressed Daphnis nerii transcripts in the infected midgut had been identified. KEGG analysis showed that protein digestion and absorption, Toll and Imd signaling pathway were down-regulated. Based on the result, we speculated that food digestion and absorption in insect midgut might be impaired after virus infection. In addition, the down-regulation of the immune response may make D. nerii more susceptible to bacterial infections. Glycerophospholipid metabolism and xenobiotics metabolism were up-regulated. These two types of pathways may affect the viral replication and xenobiotic detoxification of insect, respectively.

CONCLUSION

These results may facilitate a better understanding of the changes in Daphnis nerii metabolism during cypovirus infection and serve as a basis for future research on the molecular mechanism of DnCPV-23 invasion.

The Novel Agrotis ipsilon Nora Virus Confers Deleterious Effects to the Fitness of Spodoptera frugiperda (Lepidoptera: Noctuidae)

In the present study, we identified a novel, positive-sense single-stranded RNA virus in the Chinese black cutworm, Agrotis ipsilon. It has a genome length of 11,312 nucleotides, excluding the poly(A) tails, and contains five open reading frames. The ORF2 encodes the conserved domains of RNA helicase and RNA-dependent RNA polymerase, while ORF4 and 5 encode three viral proteins. Herein, the A. ipsilon virus was clustered with a Helicoverpa armigera Nora virus and was thus provisionally named “Agrotis ipsilon Nora virus” (AINV). AINV was successfully transmitted into a novel host, Spodoptera frugiperda, through injection, causing a stable infection. This found the possibility of horizontal AINV transmission among moths belonging to the same taxonomic family. Nonetheless, AINV infection was deleterious to S. frugiperda and mainly mediated by antiviral and amino acid metabolism-related pathways. Furthermore, the infection significantly increased the S. frugiperda larval period but significantly reduced its moth eclosion rate. It suggests that AINV is probably to be a parasitic virus of S. frugiperda.

Characterization of the lipidomic profile of BmN cells in response to Bombyx mori cytoplasmic polyhedrosis virus infection

Bombyx mori cytoplasmic polyhedrosis virus (BmCPV)that belongs to the genus Cypovirus in the family of Reoviridae is one of the problematic pathogens in sericulture. In our previous study, we have found that lipid-related constituents in the host cellular membrane are associated with the BmCPV life cycle. It is important to note that the lipids not only affect the cellular biological processes, they also impact the virus life cycle. However, the intracellular lipid homeostasis in BmN cells after BmCPV infection remains unclear. Here, the lipid metabolism in BmCPV-infected BmN cells was studied by lipidomics analysis. Our results revealed that the intracellular lipid homeostasis was disturbed in BmN cells upon BmCPV infection. Major lipids constituents in cellular membrane were found to be significantly induced upon BmCPV infection, which included triglycerides, phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, phospholipids, glucoside ceramide, monoetherphosphatidylcholin, ceramide, ceramide phosphoethanolamine and cardiolipin. Further analysis of the pathways related to these altered lipids (such as PE and PC) showed that glycerophospholipid metabolism was one of the most enriched pathways. These results suggested that BmCPV may manipulate the lipid metabolism of cells for their own interest. The findings may facilitate a better understanding of the roles of lipid metabolic changes during virus infection in future studies.

Transcriptomic signatures of cold adaptation and heat stress in the winter ant (Prenolepis imparis)

Climate change is a serious threat to biodiversity; it is therefore important to understand how animals will react to this stress. Ectotherms, such as ants, are especially sensitive to the climate as the environmental temperature influences myriad aspects of their biology, from optimal foraging time to developmental rate. In this study, we conducted an RNA-seq analysis to identify stress-induced genes in the winter ant (Prenolepis imparis). We quantified gene expression during heat and cold stress relative to a control temperature. From each of our conditions, we sequenced the transcriptome of three individuals. Our de novo assembly included 13,324 contigs that were annotated against the nr and SwissProt databases. We performed gene ontology and enrichment analyses to gain insight into the physiological processes involved in the stress response. We identified a total of 643 differentially expressed genes across both treatments. Of these, only seven genes were differentially expressed in the cold-stressed ants, which could indicate that the temperature we chose for trials did not induce a strong stress response, perhaps due to the cold adaptations of this species. Conversely, we found a strong response to heat: 426 upregulated genes and 210 downregulated genes. Of these, ten were expressed at a greater than ten-fold change relative to the control. The transcripts we could identify included those encoding for protein folding genes, heat shock proteins, histones, and Ca2+ ion transport. One of these transcripts, hsc70-4L was found to be under positive selection. We also characterized the functional categories of differentially expressed genes. These candidate genes may be functionally conserved and relevant for related species that will deal with rapid climate change.

Antimicrobial Peptides as Potential Antiviral Factors in Insect Antiviral Immune Response

Antimicrobial peptides (AMPs) with antiviral activity (antiviral peptides: AVPs) have become a research hotspot and already show immense potential to become pharmaceutically available antiviral drugs. AVPs have exhibited huge potential in inhibiting viruses by targeting various stages of their life cycle. Insects are the most speciose group of animals that inhabit almost all ecosystems and habitats on the land and are a rich source of natural AMPs. However, insect AVP mining, functional research, and drug development are still in their infancy. This review aims to summarize the currently validated insect AVPs, explore potential new insect AVPs and to discuss their possible mechanism of synthesis and action, with a view to providing clues to unravel the mechanisms of insect antiviral immunity and to develop insect AVP-derived antiviral drugs.

circEgg regulates histone H3K9me3 by sponging bmo-miR-3391-5p and encoding circEgg-P122 protein in the silkworm, Bombyx mori

A large number of circular RNAs (circRNAs) have been found in different organisms; however, their function in the regulation of histone modification remains unknown. In this study, we found that the circRNA circEgg, cyclized by the 9th-13th exon of Bombyx mori histone-lysine N-methyltransferase eggless (BmEgg) gene, mainly distributes in the cytoplasm, its expression levels changed with silkworm developmental stages, and the linear transcript level of the BmEgg gene was decreased when circEgg was overexpressed. Moreover, circEgg was found to repress histone H3 lysine 9 methylation (H3K9me3), promote histone H3 lysine 9 acetylation (H3K9ac), and positively regulate histone deacetylase (HDAC) Rpd3 (BmHDAC Rpd3) gene expression by sponging the microRNA bmo-miR-3391-5p. Furthermore, circEgg encodes a circEgg-P122 protein which appears to inhibit H3K9me3. These results suggest that circEgg regulates histone modification by sponging bmo-miR-3391-5p and encoding circEgg-P122 protein. To our knowledge, this is the first report showing that a circRNA produced by BmEgg plays an important role in histone epigenetic modification.

Transcriptome profiling of venom gland from wasp species: de novo assembly, functional annotation, and discovery of molecular markers

Background

Vespa velutina, one of the most aggressive and fearful wasps in China, can cause grievous allergies and toxic reactions, leading to organ failure and even death. However, there is little evidence on molecular data regarding wasps. Therefore, we aimed to provide an insight into the transcripts expressed in the venom gland of wasps.

Results

In our study, high-throughput RNA sequencing was performed using the venom glands of four wasp species. First, the mitochondrial cytochrome C oxidase submit I (COI) barcoding and the neighbor joining (NJ) tree were used to validate the unique identity and lineage of each individual species. After sequencing, a total of 127,630 contigs were generated and 98,716 coding domain sequences (CDS) were predicted from the four species. The Gene ontology (GO) enrichment analysis of unigenes revealed their functional role in important biological processes (BP), molecular functions (MF) and cellular components (CC). In addition, c-type, p1 type, p2 type and p3 type were the most commonly found simple sequence repeat (SSR) types in the four species of wasp transcriptome. There were differences in the distribution of SSRs and single nucleotide polymorphisms (SNPs) among the four wasp species.

Conclusions

The transcriptome data generated in this study will improve our understanding on bioactive proteins and venom-related genes in wasp venom gland and provide a basis for pests control and other applications. To our knowledge, this is the first study on the identification of large-scale genomic data and the discovery of microsatellite markers from V. tropica ducalis and V. analis fabricius.

Comparative Identification of MicroRNAs in Apis cerana cerana Workers' Midguts in Responseto Nosema ceranae Invasion

Here, the expression profiles and differentially expressed miRNAs (DEmiRNAs) in the midguts of Apis cerana cerana workers at 7 d and 10 d post-inoculation (dpi) with N. ceranae were investigated via small RNA sequencing and bioinformatics. Five hundred and twenty nine (529) known miRNAs and 25 novel miRNAs were identified in this study, and the expression of 16 predicted miRNAs was confirmed by Stem-loop RT-PCR. A total of 14 DEmiRNAs were detected in the midgut at 7 dpi, including eight up-regulated and six down-regulated miRNAs, while 12 DEmiRNAs were observed in the midgut at 10 dpi, including nine up-regulated and three down-regulated ones. Additionally, five DEmiRNAs were shared, while nine and seven DEmiRNAs were specifically expressed in midguts at 7 dpi and 10 dpi. Gene ontology analysis suggested some DEmiRNAs and corresponding target mRNAs were involved in various functions including immune system processes and response to stimulus. KEGG pathway analysis shed light on the potential functions of some DEmiRNAs in regulating target mRNAs engaged in material and energy metabolisms, cellular immunity and the humoral immune system. Further investigation demonstrated a complex regulation network between DEmiRNAs and their target mRNAs, with miR-598-y, miR-252-y, miR-92-x and miR-3654-y at the center. Our results can facilitate future exploration of the regulatory roles of miRNAs in host responses to N. ceranae, and provide potential candidates for further investigation of the molecular mechanisms underlying eastern honeybee-microsporidian interactions.

Transcriptomic investigation of immune responses of the Apis cerana cerana larval gut infected by Ascosphaera apis

Chalkbrood is the most common fungal disease in honeybees. The objective of this study was to reveal immune responses in the Apis cerana cerana larval gut following Ascosphaera apis invasion. Combining a previously assembled transcriptome of A. c. cerana larval gut and the high-throughput sequencing data obtained in this study, 6152 differentially expressed genes (DEGs) were clustered into eight profiles. Trend analysis showed three significant up-regulated profiles (p ≤ 0.05) and three down-regulated profiles. Gene Ontology (GO) term analysis suggested that DEGs within significant up-regulated and down-regulated clusters were enriched in 46 and 38 functional groups, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis indicated a majority of DEGs were involved in ribosome structure or function, carbon metabolism, biosynthesis of amino acids, and oxidative phosphorylation. In addition, 142 and 14 DEGs were annotated in the cellular immune- and humoral immune-related pathways, respectively. Further investigation indicated that DEGs up-regulated in cellular immune and humoral immune pathways outnumbered those that were down-regulated. Moreover, immune responses of A. c. cerana and Apis mellifera ligustica larvae were compared and studied to decipher resistance of eastern honeybee larvae to A. apis. These results demonstrated that a large number of genes involved in immunity-related pathways were activated by A. apis. Our findings provided valuable information for elucidating the molecular mechanisms underlying immune responses of A. c. cerana larvae to A. apis infection and pathogen-host interactions during chalkbrood infection.

Stimulator of interferon genes (STING) provides insect antiviral immunity by promoting Dredd caspase-mediated NF-κB activation

The antiviral cGMP-AMP (cGAMP)-stimulator of interferon genes (STING) pathway is well characterized in mammalian cells. However, whether this pathway also plays a role in insect antiviral immunity is unknown. In this study, we found that cGAMP is produced in silkworm (Bombyx mori) cells infected with nucleopolyhedrovirus (NPV). In searches for STING-related sequences, we identified BmSTING, a potential cGAMP sensor in B. mori We observed that BmSTING overexpression effectively inhibits NPV replication in silkworm larvae, whereas dsRNA-mediated BmSTING knockdown resulted in higher viral load. Cleavage and nuclear translocation of BmRelish, a NF-κB-related transcription factor, was also observed when BmSTING was overexpressed and was enhanced by cGAMP stimulation or viral infection of B. mori larvae. Moreover, we identified a caspase-8-like protein (BmCasp8L) as a BmSTING-interacting molecule and as a suppressor of BmSTING-mediated BmRelish activation. Interestingly, cGAMP stimulation decreased BmCasp8L binding to BmSTING and increased BmRelish activity. Of note, an interaction between death-related ced-3/Nedd2-like caspase (BmDredd) and BmSTING promoted BmRelish cleavage for efficient antiviral signaling and protection of insect cells from viral infection. Our findings have uncovered BmSTING as a critical mediator of antiviral immunity in the model insect B. mori and have identified several BmSTING-interacting proteins that control antiviral defenses.

Clathrin-mediated endocytosis is a candidate entry sorting mechanism for Bombyx mori cypovirus

Bombyx mori cypovirus (BmCPV), a member of the Reoviridae, specifically infects silkworms and causes extensive economic losses to the sericulture industry. To date, the entry mechanism of BmCPV into cells is unclear. Here we used electron microscopy to study the route of entry of BmCPV into cells, and the results demonstrated that the entry of BmCPV into BmN cells was mediated by endocytosis. Blocking the entry pathway with four endocytosis inhibitors, including dansylcadaverine, chlorpromazine, genistein, and PP2, significantly decreased the infectivity of BmCPV. This indicates that BmCPV enters BmN cells via endocytosis, and that clathrin-mediated sorting is the predominant entry method. After the relative expression levels of clathrin heavy chain (clathrin, GenBank accession No. NM_001142971.1) and the adaptor protein complex-1 gamma subunit AP-1 (AP-1, GenBank accession No. JQ824201.1), which are involved in clathrin-mediated endocytosis, were inhibited by RNA interference or abolishing the functions of clathrin and AP-1 with their corresponding antibodies, the infectivity of BmCPV was reduced significantly, which suggests that clathrin-mediated endocytosis contributed to the entry of BmCPV into cells. Our findings suggest that the clathrin-mediated endocytosis pathway is a candidate for the development of therapeutics for silkworm cytoplasmic polyhedrosis.

Discovery of anti-viral molecules and their vital functions in Bombyx mori

The silkworm Bombyx mori (B. mori), a lepidopteran model organism, has become an important model for molecular biology researches with its genome completely sequenced. Silkworms confront different types of virus diseases, mainly including those caused by Bombyx mori nucleopolyhedrovirus (BmNPV), Bombyx mori densovirus type 1 (BmDNV-1), Bombyx mori bidesovirus (BmBDV) which was termed as Bombyx mori densovirus type 2 (BmDNV-2) or Bombyx mori parvo-like virus (BmPLV) before in sericulture. B. mori offers excellent models to study the molecular mechanisms of insect innate immune responses to viruses. A variety of molecules and pathways have been identified to be involved in the immune responses in the silkworm to viruses, such as the antimicrobial peptides, prophenoloxidase-activating system, apoptosis, ROS, small RNA and related molecules. Here in this review, we summarize the current research advances in molecules involved in silkworm anti-virus pathways. Moreover, taking BmNPV as an example, we proposed a schematic model of molecules and pathways involved in silkworm immune responses against virus infection. We hope this review can facilitate further study of antiviral mechanisms in silkworm, and provide a reference for virus diseases in other organisms.

DNA methylation in silkworm genome may provide insights into epigenetic regulation of response to Bombyx mori cypovirus infection

DNA methylation is an important epigenetic modification that regulates a wide range of biological processes including immune response. However, information on the epigenetics-mediated immune mechanisms in insects is limited. Therefore, in this study, we examined transcriptomes and DNA methylomes in the fat body and midgut tissues of silkworm, Bombyx mori with or without B. mori cytoplasmic polyhedrosis virus (BmCPV) infection. The transcriptional profile and the genomic DNA methylation patterns in the midgut and fat body were tissue-specific and dynamically altered after BmCPV challenge. KEGG pathway analysis revealed that differentially methylated genes (DMGs) could be involved in pathways of RNA transport, RNA degradation, nucleotide excision repair, DNA replication, etc. 27 genes were shown to have both differential expression and differential methylation in the midgut and fat body of infected larvae, respectively, indicating that the BmCPV infection-induced expression changes of these genes could be mediated by variations in DNA methylation. BS-PCR validated the hypomethylation of G2/M phase-specific E3 ubiquitin-protein ligase-like gene in the BmCPV infected midgut. These results demonstrated that epigenetic regulation may play roles in host-virus interaction in silkworm and would be potential value for further studies on mechanism of BmCPV epithelial-specific infection and epigenetic regulation in the silkworm.

Advances in the application of high-throughput sequencing in invertebrate virology

Over the last decade, advances in high-throughput sequencing technologies have revolutionised biological research, making it possible for DNA/RNA sequencing of any organism of interest to be undertaken. Sequencing approaches are now routinely used in the detection and characterisation of (novel) viruses, investigation of host-pathogen interactions, and effective development of disease treatment strategies. For the sequencing and identification of viruses of interest, metagenomics approaches using infected host tissue are frequently used, as it is not always possible to culture and isolate these pathogens. High-throughput sequencing can also be used to investigate host-pathogen interactions by investigating (temporal) transcriptomic responses of both the host and virus, potentially leading to the discovery of novel opportunities for treatment and drug targets. In addition, viruses in environmental samples (e.g. water or soil samples) can be identified using eDNA/metagenomics approaches. The promise that recent developments in sequencing brings to the field of invertebrate virology are not devoid of technical challenges, including the need for better laboratory and bioinformatics strategies to sequence and assemble virus genomes within complex tissue or environmental samples, and the difficulties associated with the annotation of the large number of novel viruses being discovered.

Viruses of insects reared for food and feed

The use of insects as food for humans or as feed for animals is an alternative for the increasing high demand for meat and has various environmental and social advantages over the traditional intensive production of livestock. Mass rearing of insects, under insect farming conditions or even in industrial settings, can be the key for a change in the way natural resources are utilized in order to produce meat, animal protein and a list of other valuable animal products. However, because insect mass rearing technology is relatively new, little is known about the different factors that determine the quality and yield of the production process. Obtaining such knowledge is crucial for the success of insect-based product development. One of the issues that is likely to compromise the success of insect rearing is the outbreak of insect diseases. In particular, viral diseases can be devastating for the productivity and the quality of mass rearing systems. Prevention and management of viral diseases imply the understanding of the different factors that interact in insect mass rearing. This publication provides an overview of the known viruses in insects most commonly reared for food and feed. Nowadays with large-scale sequencing techniques, new viruses are rapidly being discovered. We discuss factors affecting the emergence of viruses in mass rearing systems, along with virus transmission routes. Finally we provide an overview of the wide range of measures available to prevent and manage virus outbreaks in mass rearing systems, ranging from simple sanitation methods to highly sophisticated methods including RNAi and transgenics.

Integrin beta and receptor for activated protein kinase C are involved in the cell entry of Bombyx mori cypovirus

Receptor-mediated endocytosis using a β1 integrin-dependent internalization was considered as the primary mechanism for the initiation of mammalian reovirus infection. Bombyx mori cypovirus (BmCPV) is a member of Reoviridae family which mainly infects the midgut epithelium of silkworm; the cell entry of BmCPV is poorly explored. In this study, co-immunoprecipitation (Co-IP), virus overlay protein binding assay (VOPBA), and BmCPV-protein interaction on the polyvinylidene difluoride membrane (BmCPV-PI-PVDF) methods were employed to screen the interacting proteins of BmCPV, and several proteins including integrin beta and receptor for activated protein kinase C (RACK1) were identified as the candidate interacting proteins for establishing the infection of BmCPV. The infectivity of BmCPV was investigated in vivo and in vitro by RNA interference (RNAi) and antibody blocking methods, and the results showed that the infectivity of BmCPV was significantly reduced by either small interfering RNA-mediated silencing of integrin beta and RACK1 or antibody blocking of integrin beta and RACK1. The expression level of integrin beta or RACK1 is not the highest in the silkworm midgut which is a principal target tissue of BmCPV, suggesting that the molecules other than integrin beta or RACK1 might play a key role in determining the tissue tropism of BmCPV infection. The establishment of BmCPV infection depends on other factors, and these factors interacted with integrin beta and RACK1 to form receptor complex for the cell entry of BmCPV.

Transcriptome analysis of interactions between silkworm and cytoplasmic polyhedrosis virus

Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) specifically infects silkworm midgut (MG) and multiplication occurs mainly in posterior midgut (PM). In this study, MG and fat body (FB) were extracted at 0, 3, 24, and 72 h after BmCPV infection. The total sequence reads of each sample were more than 1510000, and the mapping ratio exceeded 95.3%. Upregulated transcripts increased in MG during the infection process. Gene ontology (GO) categories showed that antioxidants were all upregulated in FB but not in MG. BGI001299, BGI014434, BGI012068, and BGI009201 were MG-specific genes with transmembrane transport function, the expression of which were induced by BmCPV. BGI001299, BGI014434, and BGI012068 expressed in entire MG and may be involved in BmCPV invasion. BGI009201 expressed only in PM and may be necessary for BmCPV proliferation. BmPGRP-S2 and BGI012452 (a putative serine protease) were induced by BmCPV and may be involved in immune defense against BmCPV. The expression level of BmCPV S1, S2, S3, S6, and S7 was high and there was no expression of S9 in MG 72 h, implying that the expression time of structural protein coding genes is earlier. These results provide insights into the mechanism of BmCPV infection and host defense.