Drosophila S2 cells are non-permissive for vaccinia virus DNA replication following entry via low pH-dependent endocytosis and early transcription

A contemporary review of clade-specific virological differences in monkeypox viruses

BACKGROUND

Monkeypox virus (MPXV) is an emerging zoonotic virus that has had on-going public health impacts in endemic regions of Central and West Africa for over a half-century. Historically, the MPXV clade endemic in regions of Central Africa is associated with higher morbidity and mortality as compared with the clade endemic in West Africa.

OBJECTIVES

Here, we review the virological characteristics of MPXV and discuss potential relationships between virulence factors and clade- (and subclade-) specific differences in virulence and transmission patterns.

SOURCES

Targeted search was conducted in PubMed using ((monkeypox virus) OR (Orthopoxvirus)) AND (zoonosis)) OR ((monkeypox) OR (human mpox).

CONTENT

Forty-seven references were considered that included three publicly available data reports and/or press releases, one book chapter, and 44 published manuscripts.

IMPLICATIONS

Although zoonosis has been historically linked to emergence events in humans, epidemiological analyses of more recent outbreaks have identified increasing frequencies of human-to-human transmission. Furthermore, viral transmission during the 2022 global human mpox outbreak, caused by a recently identified MPXV subclade, has relied exclusively on human-to-human contact with no known zoonotic link.

Inhibition of vaccinia virus L1 N-myristoylation by the host N-myristoyltransferase inhibitor IMP-1088 generates non-infectious virions defective in cell entry

We have recently shown that the replication of rhinovirus, poliovirus and foot-and-mouth disease virus requires the co-translational N-myristoylation of viral proteins by human host cell N-myristoyltransferases (NMTs), and is inhibited by treatment with IMP-1088, an ultrapotent small molecule NMT inhibitor. Here, we examine the importance of N-myristoylation during vaccinia virus (VACV) infection in primate cells and demonstrate the anti-poxviral effects of IMP-1088. N-myristoylated proteins from VACV and the host were metabolically labelled with myristic acid alkyne during infection using quantitative chemical proteomics. We identified VACV proteins A16, G9 and L1 to be N-myristoylated. Treatment with NMT inhibitor IMP-1088 potently abrogated VACV infection, while VACV gene expression, DNA replication, morphogenesis and EV formation remained unaffected. Importantly, we observed that loss of N-myristoylation resulted in greatly reduced infectivity of assembled mature virus particles, characterized by significantly reduced host cell entry and a decline in membrane fusion activity of progeny virus. While the N-myristoylation of VACV entry proteins L1, A16 and G9 was inhibited by IMP-1088, mutational and genetic studies demonstrated that the N-myristoylation of L1 was the most critical for VACV entry. Given the significant genetic identity between VACV, monkeypox virus and variola virus L1 homologs, our data provides a basis for further investigating the role of N-myristoylation in poxviral infections as well as the potential of selective NMT inhibitors like IMP-1088 as broad-spectrum poxvirus inhibitors.

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.

Identification of CP77 as the Third Orthopoxvirus SAMD9 and SAMD9L Inhibitor with Unique Specificity for a Rodent SAMD9L

Orthopoxviruses (OPXVs) have a broad host range in mammalian cells, but Chinese hamster ovary (CHO) cells are nonpermissive for vaccinia virus (VACV). Here, we revealed a species-specific difference in host restriction factor SAMD9L as the cause for the restriction and identified orthopoxvirus CP77 as a unique inhibitor capable of antagonizing Chinese hamster SAMD9L (chSAMD9L). Two known VACV inhibitors of SAMD9 and SAMD9L (SAMD9&L), K1 and C7, can bind human and mouse SAMD9&L, but neither can bind chSAMD9L. Clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 knockout of chSAMD9L from CHO cells removed the restriction for VACV, while ectopic expression of chSAMD9L imposed the restriction for VACV in a human cell line, demonstrating that chSAMD9L is a potent restriction factor for VACV. In contrast to K1 and C7, cowpox virus CP77 can bind chSAMD9L and rescue VACV replication in cells expressing chSAMD9L, indicating that CP77 is yet another SAMD9L inhibitor but has a unique specificity for chSAMD9L. Binding studies showed that the N-terminal 382 amino acids of CP77 were sufficient for binding chSAMD9L and that both K1 and CP77 target a common internal region of SAMD9L. Growth studies with nearly all OPXV species showed that the ability of OPXVs to antagonize chSAMD9L correlates with CP77 gene status and that a functional CP77 ortholog was maintained in many OPXVs, including monkeypox virus. Our data suggest that a species-specific difference in rodent SAMD9L poses a barrier for cross-species OPXV infection and that OPXVs have evolved three SAMD9&L inhibitors with different specificities to overcome this barrier.IMPORTANCE Several OPXV species, including monkeypox virus and cowpox virus, cause zoonotic infection in humans. They are believed to use wild rodents as the reservoir or intermediate hosts, but the host or viral factors that are important for OPXV host range in rodents are unknown. Here, we showed that the abortive replication of several OPXV species in a Chinese hamster cell line was caused by a species-specific difference in the host antiviral factor SAMD9L, suggesting that SAMD9L divergence in different rodent species poses a barrier for cross-species OPXV infection. While the Chinese hamster SAMD9L could not be inhibited by two previously identified OPXV inhibitors of human and mouse SAMD9&L, it can be inhibited by cowpox virus CP77, indicating that OPXVs encode three SAMD9&L inhibitors with different specificities. Our data suggest that OPXV host range in broad rodent species depends on three SAMD9&L inhibitors with different specificities.

Vaccinia Virus Transcriptome Analysis by RNA Sequencing

RNA-sequencing (RNA-Seq) using next-generation sequencing (NGS) technique is a powerful tool for simultaneous analysis of global transcripts from both vaccinia virus and host cell. Here, we describe an RNA-Seq method for analyzing the vaccinia virus transcriptome from virus-infected HeLa cells. We pay particular attention to vaccinia virus-specific aspects of sample preparation, sequencing, and data analyses, but our method could be modified to analyze transcriptomes of other cells or tissues infected with different poxviruses.

p38b and JAK-STAT signaling protect against Invertebrate iridescent virus 6 infection in Drosophila

The fruit fly Drosophila melanogaster is a powerful model system for the study of innate immunity in vector insects as well as mammals. For vector insects, it is particularly important to understand all aspects of their antiviral immune defenses, which could eventually be harnessed to control the transmission of human pathogenic viruses. The immune responses controlling RNA viruses in insects have been extensively studied, but the response to DNA virus infections is poorly characterized. Here, we report that infection of Drosophila with the DNA virus Invertebrate iridescent Virus 6 (IIV-6) triggers JAK-STAT signaling and the robust expression of the Turandots, a gene family encoding small secreted proteins. To drive JAK-STAT signaling, IIV-6 infection more immediately induced expression of the unpaireds, a family of IL-6-related cytokine genes, via a pathway that required one of the three Drosophila p38 homologs, p38b. In fact, both Stat92E and p38b were required for the survival of IIV-6 infected flies. In addition, in vitro induction of the unpaireds required an NADPH-oxidase, and in vivo studies demonstrated Nox was required for induction of TotA. These results argue that ROS production, triggered by IIV-6 infection, leads to p38b activation and unpaired expression, and subsequent JAK-STAT signaling, which ultimately protects the fly from IIV-6 infection.

Mosquitoes and other biting insects transmit many harmful pathogens to humans, including parasites and viruses. In order to better protect humans from these diseases, we must gain a more complete understanding of how insects successfully—or unsuccessfully—combat these infections. While we know a great deal regarding how insects combat RNA viruses, we know little about their immune response to DNA virus infections. Studies of DNA virus infections may reveal novel immune mechanisms, which could be uniquely effective against DNA virus infections or could be broadly effective against many viruses. In this study, we utilized an invertebrate DNA virus, IIV-6, infection model with the fruit fly Drosophila melanogaster, and found that virus infection activated several innate immune signaling pathways, which help protect the animal against this virus. Eventually, a more complete understanding of the antiviral responses of insects may be useful to restrict virus infections of disease transmitting insects.

A comparative review of viral entry and attachment during large and giant dsDNA virus infections

Viruses enter host cells via several mechanisms, including endocytosis, macropinocytosis, and phagocytosis. They can also fuse at the plasma membrane and can spread within the host via cell-to-cell fusion or syncytia. The mechanism used by a given viral strain depends on its external topology and proteome and the type of cell being entered. This comparative review discusses the cellular attachment receptors and entry pathways of dsDNA viruses belonging to the families Adenoviridae, Baculoviridae, Herpesviridae and nucleocytoplasmic large DNA viruses (NCLDVs) belonging to the families Ascoviridae, Asfarviridae, Iridoviridae, Phycodnaviridae, and Poxviridae, and giant viruses belonging to the families Mimiviridae and Marseilleviridae as well as the proposed families Pandoraviridae and Pithoviridae. Although these viruses have several common features (e.g., topology, replication and protein sequence similarities) they utilize different entry pathways to infect wide-range of hosts, including humans, other mammals, invertebrates, fish, protozoa and algae. Similarities and differences between the entry methods used by these virus families are highlighted, with particular emphasis on viral topology and proteins that mediate viral attachment and entry. Cell types that are frequently used to study viral entry are also reviewed, along with other factors that affect virus-host cell interactions.

Suppression of Poxvirus Replication by Resveratrol

Poxviruses continue to cause serious diseases even after eradication of the historically deadly infectious human disease, smallpox. Poxviruses are currently being developed as vaccine vectors and cancer therapeutic agents. Resveratrol is a natural polyphenol stilbenoid found in plants that has been shown to inhibit or enhance replication of a number of viruses, but the effect of resveratrol on poxvirus replication is unknown. In the present study, we found that resveratrol dramatically suppressed the replication of vaccinia virus (VACV), the prototypic member of poxviruses, in various cell types. Resveratrol also significantly reduced the replication of monkeypox virus, a zoonotic virus that is endemic in Western and Central Africa and causes human mortality. The inhibitory effect of resveratrol on poxviruses is independent of VACV N1 protein, a potential resveratrol binding target. Further experiments demonstrated that resveratrol had little effect on VACV early gene expression, while it suppressed VACV DNA synthesis, and subsequently post-replicative gene expression.

Membrane fusion during poxvirus entry

Poxviruses comprise a large family of enveloped DNA viruses that infect vertebrates and invertebrates. Poxviruses, unlike most DNA viruses, replicate in the cytoplasm and encode enzymes and other proteins that enable entry, gene expression, genome replication, virion assembly and resistance to host defenses. Entry of vaccinia virus, the prototype member of the family, can occur at the plasma membrane or following endocytosis. Whereas many viruses encode one or two proteins for attachment and membrane fusion, vaccinia virus encodes four proteins for attachment and eleven more for membrane fusion and core entry. The entry-fusion proteins are conserved in all poxviruses and form a complex, known as the Entry Fusion Complex (EFC), which is embedded in the membrane of the mature virion. An additional membrane that encloses the mature virion and is discarded prior to entry is present on an extracellular form of the virus. The EFC is held together by multiple interactions that depend on nine of the eleven proteins. The entry process can be divided into attachment, hemifusion and core entry. All eleven EFC proteins are required for core entry and at least eight for hemifusion. To mediate fusion the virus particle is activated by low pH, which removes one or more fusion repressors that interact with EFC components. Additional EFC-interacting fusion repressors insert into cell membranes and prevent secondary infection. The absence of detailed structural information, except for two attachment proteins and one EFC protein, is delaying efforts to determine the fusion mechanism.

Virus-Host Interactions: From Unbiased Genetic Screens to Function

Deciphering the many interactions that occur between a virus and host cell over the course of infection is paramount to understanding mechanisms of pathogenesis and to the future development of antiviral therapies. Over the past decade, researchers have started to understand these complicated relationships through the development of methodologies, including advances in RNA interference, proteomics, and the development of genetic tools such as haploid cell lines, allowing high-throughput screening to identify critical contact points between virus and host. These advances have produced a wealth of data regarding host factors hijacked by viruses to promote infection, as well as antiviral factors responsible for subverting viral infection. This review highlights findings from virus-host screens and discusses our thoughts on the direction of screening strategies moving forward.

Vaccinia reporter viruses for quantifying viral function at all stages of gene expression

Poxviruses are a family of double stranded DNA viruses that include active human pathogens such as monkeypox, molluscum contagiousum, and Contagalo virus. The family also includes the smallpox virus, Variola. Due to the complexity of poxvirus replication, many questions still remain regarding their gene expression strategy. In this article we describe the conceptualization and usage of recombinant vaccinia viruses that enable real-time measurement of single and multiple stages of viral gene expression in a high-throughput format. This is enabled through the use of spectrally distinct fluorescent proteins as reporters for each of three stages of viral replication. These viruses provide a high signal-to-noise ratio while retaining stage specific expression patterns, enabling plate-based assays and microscopic observations of virus propagation and replication. These tools have uses for antiviral discovery, studies of the virus-host interaction, and evolutionary biology.

Role of the vaccinia virus O3 protein in cell entry can be fulfilled by its Sequence flexible transmembrane domain

The vaccinia virus O3 protein, a component of the entry-fusion complex, is encoded by all chordopoxviruses. We constructed truncation mutants and demonstrated that the transmembrane domain, which comprises two-thirds of this 35 amino acid protein, is necessary and sufficient for interaction with the entry-fusion complex and function in cell entry. Nevertheless, neither single amino acid substitutions nor alanine scanning mutagenesis revealed essential amino acids within the transmembrane domain. Moreover, replication-competent mutant viruses were generated by randomization of 10 amino acids of the transmembrane domain. Of eight unique viruses, two contained only two amino acids in common with wild type and the remainder contained one or none within the randomized sequence. Although these mutant viruses formed normal size plaques, the entry-fusion complex did not co-purify with the mutant O3 proteins suggesting a less stable interaction. Thus, despite low specific sequence requirements, the transmembrane domain is sufficient for function in entry.

Human genome-wide RNAi screen reveals a role for nuclear pore proteins in poxvirus morphogenesis

Poxviruses are considered less dependent on host functions than other DNA viruses because of their cytoplasmic site of replication and large genomes, which encode enzymes for DNA and mRNA synthesis. Nevertheless, RNAi screens with two independent human genome-scale libraries have identified more than 500 candidate genes that significantly inhibited and a similar number that enhanced replication and spread of infectious vaccinia virus (VACV). Translational, ubiquitin-proteosome, and endoplasmic reticulum-to-Golgi transport functions, known to be important for VACV, were enriched in the siRNA-inhibiting group, and RNA polymerase II and associated functions were enriched in the siRNA-enhancing group. Additional findings, notably the inhibition of VACV spread by siRNAs to several nuclear pore genes, were unanticipated. Knockdown of nucleoporin 62 strongly inhibited viral morphogenesis, with only a modest effect on viral gene expression, recapitulating and providing insight into previous studies with enucleated cells.

Degradation of host microRNAs by poxvirus poly(A) polymerase reveals terminal RNA methylation as a protective antiviral mechanism

The life cycle of several viruses involves host or virally encoded small noncoding RNAs, which play important roles in posttranscriptional regulation. Small noncoding RNAs include microRNAs (miRNAs), which modulate the transcriptome, and small interfering RNAs (siRNAs), which are involved in pathogen defense in plants, worms, and insects. We show that insect and mammalian poxviruses induce the degradation of host miRNAs. The virally encoded poly(A) polymerase, which polyadenylates viral transcripts, also mediates 3' polyadenylation of host miRNAs, resulting in their degradation by the host machinery. In contrast, siRNAs, which are protected by 2'O-methylation (2'OMe), were not targeted by poxviruses. These findings suggest that poxviruses may degrade host miRNAs to promote replication and that virus-mediated small RNA degradation likely contributed to 2'OMe evolution.

Drosophila heparan sulfate 6-O-endosulfatase Sulf1 facilitates wingless (Wg) protein degradation

Heparan sulfate proteoglycans regulate various physiological and developmental processes through interactions with a number of protein ligands. Heparan sulfate (HS)-ligand binding depends on the amount and patterns of sulfate groups on HS, which are controlled by various HS sulfotransferases in the Golgi apparatus as well as extracellular 6-O-endosulfatases called "Sulfs." Sulfs are a family of secreted molecules that specifically remove 6-O-sulfate groups within the highly sulfated regions on HS. Vertebrate Sulfs promote Wnt signaling, whereas the only Drosophila homologue of Sulfs, Sulf1, negatively regulates Wingless (Wg) signaling. To understand the molecular mechanism for the negative regulation of Wg signaling by Sulf1, we studied the effects of Sulf1 on HS-Wg interaction and Wg stability. Sulf1 overexpression strongly inhibited the binding of Wg to Dally, a potential target heparan sulfate proteoglycan of Sulf1. This effect of Drosophila Sulf1 on the HS-Wg interaction is similar to that of vertebrate Sulfs. Using in vitro, in vivo, and ex vivo systems, we show that Sulf1 reduces extracellular Wg protein levels, at least partly by facilitating Wg degradation. In addition, expression of human Sulf1 in the Drosophila wing disc lowers the levels of extracellular Wg protein, as observed for Drosophila Sulf1. Our study demonstrates that vertebrate and Drosophila Sulfs have an intrinsically similar activity and that the function of Sulfs in the fate of Wnt/Wg ligands is context-dependent.

Staphylococcus aureus α-toxin modulates skin host response to viral infection

BACKGROUND

Patients with atopic dermatitis (AD) with a history of eczema herpeticum have increased staphylococcal colonization and infections. However, whether Staphylococcus aureus alters the outcome of skin viral infection has not been determined.

OBJECTIVE

We investigated whether S aureus toxins modulated host response to herpes simplex virus (HSV) 1 and vaccinia virus (VV) infections in normal human keratinocytes (NHKs) and in murine infection models.

METHODS

NHKs were treated with S aureus toxins before incubation of viruses. BALB/c mice were inoculated with S aureus 2 days before VV scarification. Viral loads of HSV-1 and VV were evaluated by using real-time PCR, a viral plaque-forming assay, and immunofluorescence staining. Small interfering RNA duplexes were used to knockdown the gene expression of the cellular receptor of α-toxin, a disintegrin and metalloprotease 10 (ADAM10). ADAM10 protein and α-toxin heptamers were detected by using Western blot assays.

RESULTS

We demonstrate that sublytic staphylococcal α-toxin increases viral loads of HSV-1 and VV in NHKs. Furthermore, we demonstrate in vivo that the VV load is significantly greater (P < .05) in murine skin inoculated with an α-toxin-producing S aureus strain compared with murine skin inoculated with the isogenic α-toxin-deleted strain. The viral enhancing effect of α-toxin is mediated by ADAM10 and is associated with its pore-forming property. Moreover, we demonstrate that α-toxin promotes viral entry in NHKs.

CONCLUSION

The current study introduces the novel concept that staphylococcal α-toxin promotes viral skin infection and provides a mechanism by which S aureus infection might predispose the host toward disseminated viral infections.

Reverse genetics analysis of poxvirus intermediate transcription factors

Vaccinia virus transcription is regulated in three stages. An intermediate transcription factor, comprised of virus-encoded polypeptides A8 and A23, was previously identified by in vitro analyses. To investigate its role, we engineered cells that stably expressed both subunits and complemented the replication of A8 and A23 deletion mutant viruses. Without A8 or A23, viral early gene expression and DNA replication occurred but intermediate and late gene expression and resolution of genome concatemers were not detected.

Poxvirus cell entry: how many proteins does it take?

For many viruses, one or two proteins enable cell binding, membrane fusion and entry. The large number of proteins employed by poxviruses is unprecedented and may be related to their ability to infect a wide range of cells. There are two main infectious forms of vaccinia virus, the prototype poxvirus: the mature virion (MV), which has a single membrane, and the extracellular enveloped virion (EV), which has an additional outer membrane that is disrupted prior to fusion. Four viral proteins associated with the MV membrane facilitate attachment by binding to glycosaminoglycans or laminin on the cell surface, whereas EV attachment proteins have not yet been identified. Entry can occur at the plasma membrane or in acidified endosomes following macropinocytosis and involves actin dynamics and cell signaling. Regardless of the pathway or whether the MV or EV mediates infection, fusion is dependent on 11 to 12 non-glycosylated, transmembrane proteins ranging in size from 4- to 43-kDa that are associated in a complex. These proteins are conserved in poxviruses making it likely that a common entry mechanism exists. Biochemical studies support a two-step process in which lipid mixing of viral and cellular membranes is followed by pore expansion and core penetration.

The membrane fusion step of vaccinia virus entry is cooperatively mediated by multiple viral proteins and host cell components

For many viruses, one or two proteins allow cell attachment and entry, which occurs through the plasma membrane or following endocytosis at low pH. In contrast, vaccinia virus (VACV) enters cells by both neutral and low pH routes; four proteins mediate cell attachment and twelve that are associated in a membrane complex and conserved in all poxviruses are dedicated to entry. The aim of the present study was to determine the roles of cellular and viral proteins in initial stages of entry, specifically fusion of the membranes of the mature virion and cell. For analysis of the role of cellular components, we used well characterized inhibitors and measured binding of a recombinant VACV virion containing Gaussia luciferase fused to a core protein; viral and cellular membrane lipid mixing with a self-quenching fluorescent probe in the virion membrane; and core entry with a recombinant VACV expressing firefly luciferase and electron microscopy. We determined that inhibitors of tyrosine protein kinases, dynamin GTPase and actin dynamics had little effect on binding of virions to cells but impaired membrane fusion, whereas partial cholesterol depletion and inhibitors of endosomal acidification and membrane blebbing had a severe effect at the later stage of core entry. To determine the role of viral proteins, virions lacking individual membrane components were purified from cells infected with members of a panel of ten conditional-lethal inducible mutants. Each of the entry protein-deficient virions had severely reduced infectivity and except for A28, L1 and L5 greatly impaired membrane fusion. In addition, a potent neutralizing L1 monoclonal antibody blocked entry at a post-membrane lipid-mixing step. Taken together, these results suggested a 2-step entry model and implicated an unprecedented number of viral proteins and cellular components involved in signaling and actin rearrangement for initiation of virus-cell membrane fusion during poxvirus entry.

Poxviruses are large DNA viruses that cause diseases in humans and other animals. To initiate infection, the core of the large, membrane-enveloped particle must penetrate into the cytoplasm where replication occurs. For most enveloped viruses only one or two proteins are needed for attachment and penetration. However, at least sixteen poxvirus proteins are dedicated to entry: four for attachment and twelve for penetration. The latter proteins form the entry fusion complex (EFC) and are conserved in all poxviruses indicating that the entry mechanism has been retained since the origin of the family. The purpose of the present study was to determine the cellular processes and poxviral proteins needed for fusion of the viral and cellular membranes. We found that a variety of inhibitors that interfered with cell signaling and reorganization of the actin cytoskeleton prevented membrane fusion as determined by lipid mixing, whereas others targeted the subsequent stage in entry. In addition, seven viral protein components of the EFC were required for the initial membrane fusion step, whereas three were not. A neutralizing monoclonal antibody to one of the latter also did not interfere with membrane lipid mixing but still prevented core entry supporting a 2-step poxvirus entry model.

Drosophila melanogaster S2 cells for expression of heterologous genes: From gene cloning to bioprocess development

In the present review we discuss strategies that have been used for heterologous gene expression in Drosophila melanogaster Schneider 2 (S2) cells using plasmid vectors. Since the growth of S2 cells is not dependent on anchorage to solid substrates, these cells can be easily cultured in suspension in large volumes. The factors that most affect the growth and gene expression of S2 cells, namely cell line, cell passage, inoculum concentration, culture medium, temperature, dissolved oxygen concentration, pH, hydrodynamic forces and toxic metabolites, are discussed by comparison with other insect and mammalian cells. Gene expression, cell metabolism, culture medium formulation and parameters involved in cellular respiration are particularly emphasized. The experience of the authors with the successful expression of a biologically functional protein, the rabies virus glycoprotein (RVGP), by recombinant S2 cells is presented in the topics covered.

Baculovirus induced transcripts in hemocytes from the larvae of Heliothis virescens

Using RNA-seq digital difference expression profiling methods, we have assessed the gene expression profiles of hemocytes harvested from Heliothis virescens that were challenged with Helicoverpa zea single nucleopolyhedrovirus (HzSNPV). A reference transcriptome of hemocyte-expressed transcripts was assembled from 202 million 42-base tags by combining the sequence data of all samples, and the assembled sequences were then subject to BLASTx analysis to determine gene identities. We used the fully sequenced HzSNPV reference genome to align 477,264 Illumina sequence tags from infected hemocytes in order to document expression of HzSNPV genes at early points during infection. A comparison of expression profiles of control insects to those lethally infected with HzSNPV revealed differential expression of key cellular stress response genes and genes involved in lipid metabolism. Transcriptional regulation of specific insect hormones in baculovirus-infected insects was also altered. A number of transcripts bearing homology to retroviral elements that were detected add to a growing body of evidence for extensive invasion of errantiviruses into the insect genome. Using this method, we completed the first and most comprehensive gene expression survey of both baculoviral infection and host immune defense in lepidopteran larvae.