Available lepidopteran insect cell lines

This chapter lists the known cell lines from Lepidoptera, largely based on previous compilations of insect cell lines published by W. Fred Hink. The official designation is given for each cell line as well as the species, tissue source, and, when known, the susceptibilities to baculoviruses.

Host mediated selection of pathogen genotypes as a mechanism for the maintenance of baculovirus diversity in the field

The genetic diversity of many DNA virus populations in nature is unknown, but for those that have been studied it has been found to be relatively high. This is particularly true for baculoviruses, a family of large double-stranded DNA viruses that infect the larval stages of insects. Why there should be such heterogeneity within these virus populations is puzzling and what sustains it is still unknown. It has long been recognized that some baculoviruses have a relatively wide host range, but the effect of different host species on the genotypic structure of a baculovirus population has received little attention. We provide evidence that infection of different insect species can influence the genetic diversity of a Panolis flammea nucleopolyhedrovirus (PaflNPV) population, isolated from the pine beauty moth. Variable regions of the PaflNPV genome were sequenced and novel ORFs were identified on each of the enlarged fragments. The roles of these orfs and the implications of their presence or absence within different genotypes are discussed. The variable fragments were also labelled with 32P and used as polymorphic genetic markers of genotype abundance. The proportion of polymorphic loci changed after passage in different insect species and this varied among species, suggesting a role for host selection of pathogen genotypes in the field as a mechanism for maintaining genetic diversity. These results have wide-ranging implications for understanding the ecology of insect-virus interactions in the natural environment and the evolution of baculovirus life history strategies.

A glassy-winged sharpshooter cell line supports replication of Rhopalosiphum padi virus (Dicistroviridae)

Rhopalosiphum padi virus (RhPV) (family Dicistroviridae; genus Cripavirus) is an icosahedral aphid virus with a 10kb positive-sense RNA genome. To study the molecular biology of RhPV, identification of a cell line that supports replication of the virus is essential. We screened nine cell lines derived from species within the Lepidoptera, Diptera and Hemiptera for susceptibility to RhPV following RNA transfection. We observed cytopathic effects (CPE) only in cell lines derived from hemipterans, specifically GWSS-Z10 cells derived from the glassy winged sharp shooter, Homalodisca coagulata and DMII-AM cells derived from the corn leaf hopper, Dalbulus maidis. Translation and appropriate processing of viral gene products, RNA replication and packaging of virus particles in the cytoplasm of GWSS-Z10 cells were examined by Western blot analysis, Northern blot hybridization and electron microscopy. Infectivity of the GWSS-Z10 cell derived-virus particles to the bird cherry-oat aphid, R. padi, was confirmed by RT-PCR and Western blot. The GWSS-Z10 cell line provides a valuable tool to investigate replication, structure and assembly of RhPV.

Genome of the most widely used viral biopesticide: Anticarsia gemmatalis multiple nucleopolyhedrovirus

The genome of Anticarsia gemmatalis multiple nucleopolyhedrovirus isolate 2D (AgMNPV-2D), which is the most extensively used virus pesticide in the world, was completely sequenced and shown to have 132 239 bp (G+C content 44.5 mol%) and to be capable of encoding 152 non-overlapping open reading frames (ORFs). Three ORFs were unique to AgMNPV-2D, one of which (ag31) had similarity to eukaryotic poly(ADP-ribose) polymerases. The lack of chiA and v-cath may explain some of the success and growth of the AgMNPV biological control programme, as it may explain the high recovery of polyhedra sequestered inside dead larvae in the field, which are collected and used for further application as biological pesticides in soybean fields. The genome organization was similar to that of the Choristoneura fumiferana defective MNPV (CfDefNPV). Most of the variation between the two genomes took place near highly repetitive regions, which were also closely associated with bro-coding regions. The separation of the NPVs into groups I and II was supported by: (i) a phenogram of the complete genomes of 28 baculovirus and Heliothis zea virus 1, (ii) the most parsimonious reconstruction of gene content along the phenograms and (iii) comparisons of genomic features. Moreover, these data also reinforced the notion that group I of the NPVs can be split further into the AgMNPV lineage (AgMNPV, CfDefNPV, Epiphyas postvittana NPV, Orgyia pseudotsugata MNPV and C. fumiferana MNPV), sharing eight defining genes, and the Autographa californica MNPV (AcMNPV) lineage (AcMNPV, Rachiplusia ou NPV and Bombyx mori NPV), sharing nine defining genes.

Genome sequence and organization of a nucleopolyhedrovirus that infects the tea looper caterpillar, Ectropis obliqua

The complete nucleotide sequence of Ectropis obliqua nucleopolyhedrovirus (EcobNPV), which infects the tea looper caterpillar, was determined and analyzed. The double stranded circular genome is composed of 131,204 bp and is 37.6% G+C rich. The analysis predicted 126 putative, minimally overlapping open reading frames (ORFs) with 150 or more nucleotides that together compose 89.8% of the genome. The remaining 10.2% constitute non-coding and three homologous regions. Comparison with previously sequenced baculoviruses indicated that three ORFs were unique to EcobNPV, while the remaining 123 ORFs shared identity with other baculovirus genes. In addition to two bro homologues, three other repeat ORFs, including dbp, p26, and odv-e66, were identified. Phylogenetic analysis indicated that each member of the paired ORFs was acquired independently. Gene parity plot analysis and percent identity of gene homologues suggested that EcobNPV is a Group II NPV, although its genomic organization was highly distinct.

Field resistance of codling moth against Cydia pomonella granulovirus (CpGV) is autosomal and incompletely dominant inherited

The current appearance of local codling moth populations with resistance to Cydia pomonella granulovirus (CpGV) is an impediment to continuous CpGV application. Therefore, crossing experiments have been performed in order to gain information about the inheritance of resistance. Evidence is presented that the observed field resistance is stably inherited even under non-selective conditions in the laboratory. Offspring of reciprocal F(1) crosses between a susceptible ('S') and a resistant ('R') strain and backcrosses between F(1) and S were bioassayed at different CpGV concentrations. The resistant strain showed 100 times lower susceptibility in 7-day bioassays. The responses of the reciprocal crosses (male S x female R and female S x male R) did not differ significantly, indicating that resistance is autosomally inherited. The median lethal concentration for the F(1) progeny was intermediate between those of its parental strains. Mortality data obtained from the backcrosses suggested that inheritance of resistance is due to a non-additive, polygenic trait.

Characterization of the Helicoverpa assulta nucleopolyhedrovirus genome and sequence analysis of the polyhedrin gene region

A local strain of Helicoverpa assulta nucleopolyhedrovirus (HasNPV) was isolated from infected H.assulta larvae in Korea. Restriction endonuclease fragment analysis, using 4 restriction enzymes, estimated that the total genome size of HasNPV is about 138 kb. A degenerate polymerase chain reaction (PCR) primer set for the polyhedrin gene successfully amplified the partial polyhedrin gene of HasNPV. The sequencing results showed that the about 430 bp PCR product was a fragment of the corresponding polyhedrin gene. Using HasNPV partial predicted polyhedrin to probe the Southern blots, we identified the location of the polyhedrin gene within the 6 kb Eco RI, 15 kb Nco I, 20 kb Xho I, 17 kb Bgl II and 3 kb Cla I fragments, respectively. The 3 kb Cla I fragment was cloned and the nucleotide sequences of the polyhedrin coding region and its flaking regions were determined. Nucleotide sequence analysis indicated the presence of an open reading frame of 735 nucleotides which could encode 245 amino acids with a predicted molecular mass of 29 kDa. The nucleotide sequences within the coding region of HasNPV polyhedrin shared 73.7% identity with the polyhedrin gene from Autographa californica NPV but were most closely related to Helicoverpa and Heliothis species NPVs with over 99% sequence identity.

Identification and functional characterization of AMVp33, a novel homolog of the baculovirus caspase inhibitor p35 found in Amsacta moorei entomopoxvirus

Members of the baculovirus p35 gene family encode proteins that specifically inhibit caspases, cysteine proteases that are involved in apoptosis. To date, p35 homologs have only been found in baculoviruses. We have identified AMVp33, a gene from Amsacta moorei entomopoxvirus with low but significant homology to baculovirus p35 genes. Expression of AMVp33 blocked apoptosis in several different insect and human cell lines. Purified recombinant P33 protein was an efficient inhibitor of insect and human effector caspases, but not initiator caspases. P33 was cleaved by effector caspases, and the resulting cleavage fragments stably associated with the caspases. Mutation of the predicted caspase cleavage site in P33 eliminated cleavage, caspase inhibition and anti-apoptotic function. Thus, AMVp33 encodes a caspase inhibitor similar to baculovirus P35 with a preference for effector caspases. This is the first report of a p35 homolog from any viral or cellular genome outside of the baculovirus family.

A recombinant truncated Cry1Ca protein is toxic to lepidopteran insects and forms large cuboidal crystals in insect cells

A truncated version of the cry1Ca gene from Bacillus thuringiensis was introduced into the genome of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) under the control of two promoters. A recombinant virus (vSyncry1c) was isolated and used to infect insect cells in culture and insect larvae. Structural and ultrastructural analysis of insects infected with vSyncry1C showed the formation of large cuboidal crystals inside the cytoplasm of insect cells in culture and in insect cadavers late in infection. Infected insect cell extracts were analyzed by SDS-PAGE and Western blot and showed the presence of a 65-kDa polypeptide probably corresponding to the protease processed form of the toxin. Bioassays using purified recombinant toxin crystals showed a CL(50) of 19.49 ng/ml for 2(nd) instar A. gemmatalis larvae and 114.1 ng/ml for S. frugiperda.

Disruption effect of Microplitis bicoloratus polydnavirus EGF-like protein, MbCRP, on actin cytoskeleton in lepidopteran insect hemocytes

Microplitis bicoloratus is a braconid endoparasitic wasp associated with the polydnavirus named Microplitis bicoloratus bracovirus (MbBV). Parasitism of Spodoptera litura larvae leads to an impaired cellular immune response and to the disappearance of the 42 kDa actin in host hemocytes. In this work, we investigated if the absence of actin in blood cells was related to MbBV infection. An MbBV gene similar to egf-like genes identified in another bracovirus was partially cloned and named Mbcrp1. The full-length gene, named Mbcrp, is transcribed throughout the course of parasitism in host hemocytes and the 30 kDa MbCRP protein was detected in hemocytes 6-7 d post-parasitization. The Mbcrp1 gene contains the cysteine-rich trypsin inhibitor-like (TIL) domain coding sequence and the expression of recombinant MbCRP1 inhibited the expression of the 42 kDa actin in Hi5 cells. The 34.1 kDa MbCRP1-green fluorescent protein fusion protein locate specifically in the cytoplasm. These results suggest that expression of MbCRP in lepidopteran insect cells is related to the disruption of the actin cytoskeleton.

Sequencing and characterisation of p74 gene in two isolates of Anticarsia gemmatalis MNPV

P74 is a protein encoded in the genome of baculoviruses, associated with the envelopes of occluded virus. Its presence proved to be essential for per os infection. In first place, in this work we designed two universal primers to amplify a sequence region of the p74 ORF in baculoviruses from different classification groups. Then, by the use of these amplicons we obtained the complete sequence of the p74 locus from two isolates of AgMNPV, 2D (Brazil) and SF (Argentina). In the flanking regions we determined the complete sequence of p10 gene and a portion of p26 gene. Comparing both p74 sequence data (ORFs of 1935 bp) we found fifteen nucleotide changes that result in six amino acid changes. Comparisons of AgMNPV p74s with other baculovirus homologous genes indicate a close relationship with other group I Nucleopolyhedrovirus, in particular CfDEFNPV. These results were based on ORF sequence, amino acid sequence and gene order. The predictive studies about secondary structure and hydrophobic index point at six regions potentially associated to its function or native conformation. Finally, the detection of p74 mRNA after virus DNA replication confirms a late expression pattern.

In vivo characterization of a group II nucleopolyhedrovirus isolated from Mamestra brassicae (Lepidoptera: Noctuidae) in Japan

A Japanese isolate of Mamestra brassicae nucleopolyhedrovirus (MabrNPV) was identified phylogenetically as a group II nucleopolyhedrovirus (NPV) that is related closely to other NPVs isolated from Mamestra spp. based on nucleotide sequence data of its polh, egt and lef-3 genes. The multiplication of MabrNPV in M. brassicae larvae was characterized following inoculation at various doses and in combination with the fluorescent brightener Tinopal by measuring temporal changes in the concentrations of its viral DNA using real-time quantitative PCR. The growth curves of budded-virus replication were analysed by fitting the data of viral DNA concentration in the host haemolymph to a modified Gompertz model. When fifth-instar larvae were inoculated with an LD95 equivalent dose of MabrNPV and Tinopal, the time lag between the onset of primary and secondary infection was estimated to be 25 h. Another 65 h was required to reach a plateau titre equivalent to a level of 10(9) virions ml(-1) in the haemolymph. All larvae died during the sixth instar following this inoculation regime. In contrast, following inoculation with a 1000-fold higher dose of MabrNPV and Tinopal, the time lag between the onset of primary and secondary infection was only 20 h. Subsequently, the same plateau titre was reached after a further 20 h. Following this inoculation regime, most larvae died during the fifth instar. Quantification of viral DNA by real-time quantitative PCR and application of the Gompertz model are valuable for the characterization of baculovirus replication in vivo.

Isolation and characterization of plaque-purified strains of Malacosoma disstria Nucleopolyhedrovirus

Seven plaque-purified genotypic variants or strains, derived from a previously described field isolate of the Malacosoma disstria Nucleopolyhedrovirus (MadiNPV) from Alberta populations of forest tent caterpillar, were characterized based on distinctive restriction endonuclease fragment patterns. Two strains, MadiNPV-pp3 and MadiNPV-pp11, were selected for further characterization, as they represented strains producing high and low budded virus (BV) titres, respectively, in the M. disstria cell line UA-Md203. Analysis of restriction endonuclease fragment profiles indicated the genomes differed significantly in size, 133.8 +/- 2.4 kb for MadiNPV-pp3 and 118.1 +/- 3.5 kb for MadiNPV-pp11. These strains were characterized based on their BV production in three different cell lines derived from M. disstria haemocytes. Compared with MadiNPV-pp11, MadiNPV-pp3 produced two- to three-fold more BVs in UA-Md203 and 210 other cell lines; however, BV production was only marginally higher for MadiNPV-pp3 in the UA-Md221 cell line. Similarly, the yield of polyhedral inclusion bodies was significantly higher for MadiNPV-pp3 in UA-Md203 and 210 cell lines than for MadiNPV-pp11 but not in the UA-Md221 cell line. This data, although derived from a limited number of cell lines, suggested MadiNPV-pp3 may have a broader tissue tropism than MadiNPV-pp11.

Quantitative estimation of Hyblaea puera NPV production in three larval stages of the teak defoliator, Hyblaea puera (Cramer)

Hyblaea puera nucleoployhedrovirus (HpNPV) is a potential biocontrol agent of the teak defoliator, Hyblaea puera (Cramer) (Lepidoptera: Hyblaeidae). To quantify the growth of the virus in the host larvae, three larval stages of the teak defoliator were subjected to quantitative bioassays using specified dilutions of HpNPV. The HpNPV production was found to be dependent on the dose, incubation period as well as stage specific responses of the host insect used. As larvae matured, production of the virus per mg body weight was not found to be in a constant proportion to the increase in the body weight. The combination which yielded the greatest virus production of 3.55 x 10(9) polyhedral occlusion bodies (POBs) was that in which larva weighing 26-37 mg was fed with 1 x 10(6) POBs, incubated for 6 h and harvested at 72 h post infection (h p.i.). The response of the fourth instar larvae was found to be more productive than the third and fifth instar larvae, which makes it an ideal candidate for mass production of the virus in vivo.

Genome sequence of an enhancin gene-rich nucleopolyhedrovirus (NPV) from Agrotis segetum: collinearity with Spodoptera exigua multiple NPV

The genome sequence of a Polish isolate of Agrotis segetum nucleopolyhedrovirus (AgseNPV-A) was determined and analysed. The circular genome is composed of 147,544 bp and has a G+C content of 45.7 mol%. It contains 153 putative, non-overlapping open reading frames (ORFs) encoding predicted proteins of more than 50 aa, together making up 89.8 % of the genome. The remaining 10.2 % of the DNA constitutes non-coding regions and homologous-repeat regions. One hundred and forty-three AgseNPV-A ORFs are homologues of previously reported baculovirus gene sequences. There are ten unique ORFs and they account for 3 % of the genome in total. All 62 lepidopteran baculovirus genes, including the 29 core baculovirus genes, were found in the AgseNPV-A genome. The gene content and gene order of AgseNPV-A are most similar to those of Spodoptera exigua (Se) multiple NPV and their shared homologous genes are 100 % collinear. Three putative enhancin genes were identified in the AgseNPV-A genome. In phylogenetic analysis, the AgseNPV-A enhancins form a cluster separated from enhancins of the Mamestra species NPVs.

Morphological, phylogenetic and biological characteristics of Ectropis obliqua single-nucleocapsid nucleopolyhedrovirus

The tea looper caterpillar, Ectropis obliqua, is one of the major pests of tea bushes. E. obliqua single-nucleocapsid nucleopolyhedrovirus (EcobSNPV) has been used as a commercial pesticide for biocontrol of this insect. However only limited genetic analysis for this important virus has been done up to now. EcobSNPV was characterized in this study. Electron microscopy analysis of the occlusion body showed polyhedra of 0.7 to 1.7 mum in diameter containing a single nucleocapsid per envelope of the virion. A 15.5 kb genomic fragment containing EcoRI-L, EcoRI-N and HindIII-F fragments, was sequenced. Analysis of the sequence revealed that the fragment contained eleven potential open reading frames (ORFs): lef-1, egt, 38.7k, rr1, polyhedrin, orf1629, pk-1, hoar and homologues to Spodoptera exigua multicapsid NPV (SeMNPV) ORFs 15, 28, and 29. Gene arrangement and phylogeny analysis suggest that EcobSNPV is closely related to the previously described Group II NPV. Bioassays on lethal concentration (LC(50) and LC(90)) and lethal time (LT(50) and LT(90)) were conducted to test the susceptibility of E. obliqua larvae to the virus.

Fossil evidence of insect pathogens

The present report describes fossil evidence of insect pathogens, heretofore, almost non-existent, from six samples of amber ranging in age from 15 to 100 million years. They include a cytoplasmic polyhedrosis virus and trypanosomatid infection in an adult biting midge (Diptera: Ceratopogonidae), and a nuclear polyhedrosis virus in an adult sand fly (Diptera: Phlebotomidae), both from Early Cretaceous Burmese amber, several types of fungal thalli on the cuticle of an adult mosquito (Culicidae: Diptera), as well as a fungal growth on the prothorax of a fungus gnat (Mycetophilidae: Diptera) in Dominican amber and large tumors in the body cavity of a caterpillar (Lepidoptera) in Mexican amber. These discoveries suggest that insect polyhedrosis viruses were present 100 million years ago and present the possibility that vertebrate arboviruses (especially those in the family Reoviridae) could have evolved from cytoplasmic polyhedrosis viruses infecting biting insects. The flagellates in the Early Cretaceous biting midge represent the first fossil record of monogenetic trypanosomatid infections of arthropods.

Small RNA Viruses of Insects: Expression in Plants and RNA Silencing

Interest in insect small RNA viruses (SRVs) has grown slowly but steadily. A number of new viruses have been analyzed at the sequence level, adding to our knowledge of their diversity at the level of both individual virus species and families. In particular, a number of possible new virus families have emerged. This research has largely been driven by interest in their potential for pest control, as well as in their importance as the causal agents of disease in beneficial arthropods. At the same time, research into known viruses has made valuable contributions to our understanding of an emerging new field of central importance to molecular biology-the existence of RNA-based gene silencing, developmental control, and adaptive immune systems in eukaryotes. Subject to RNA-based adaptive immune responses in their hosts, viruses have evolved a variety of genes encoding proteins capable of suppressing the immune response. Such genes were first identified in plant viruses, but the first examples known from animal viruses were identified in insect RNA viruses. This chapter will address the diversity of insect SRVs, and attempts to harness their simplicity in the engineering of transgenic plants expressing viruses for resistance to insect pests. We also describe RNA interference and antiviral pathways identified in plants and animals, how they have led viruses to evolve genes capable of suppressing such adaptive immunity, and the problems presented by these pathways for the strategy of expressing viruses in transgenic plants. Approaches for countering these problems are also discussed.

Influence of virus inoculation method and host larval age on productivity of the nucleopolyhedrovirus of the teak defoliator, Hyblaea puera (Cramer)

Hyblaea puera nucleopolyhedrovirus (HpNPV) is a potential biocontrol agent against the teak defoliator H. puera (Cramer) (Lepidoptera: Hyblaeidae). As part of optimization of the mass production of this nucleopolyhedrovirus, three methods of inoculation were evaluated against the host larvae with various yield parameters as selection criteria. The inoculation methods compared were controlled dose on diet in rearing tubes using a micropipette, controlled dose on leaf discs (prepared from teak leaves) using a micropipette and spraying onto diet filled rearing tubes using an atomizer. Fifth instar H. puera larvae of the weight classes 75-100, 101-125, 126-150, 151-175 and 176-200mg were used for the bioassay. With reference to percentage of harvested larvae, virus production per larva and virus production per inoculated larva (VPIL), spraying viral suspension into rearing tubes filled with artificial diet using a hand sprayer was found to be the most efficient method of inoculation. It was observed that the method of inoculation and age of the larvae has discrete as well as interactive influence on the virus yield parameters.

Molecular identification and phylogenetic analysis of baculoviruses from Lepidoptera

PCR amplification of the highly conserved baculovirus genes late expression factor 8 (lef-8), late expression factor 9 (lef-9) and polyhedrin/granulin (polh/gran) combined with molecular phylogenetic analyses provide a powerful tool to identify lepidopteran-specific baculoviruses and to study their diversity. In the present investigation, we have improved the degenerate oligonucleotides and corroborated the approach that was recently described by Lange et al. (Lange, M., Wang, H., Zhihong, H., Jehle, J.A., 2004. Towards a molecular identification and classification system of lepidopteran-specific baculoviruses. Virology 325, 36-47.). Baculovirus DNA was isolated from 71 uncharacterized historic baculovirus samples, and partial gene sequences were amplified by using gene-specific degenerate PCR primers. The obtained PCR products were directly sequenced, and the deduced amino acid sequences were compiled and aligned with published sequences of these target genes. A phylogenetic tree of 117 baculoviruses was inferred using maximum parsimony and distance methods. Based on the comprehensive phylogenetic analysis of the partial lef-8, lef-9 and polh/gran genes, we propose a phylogenetic species criterion for lepidopteran-specific baculoviruses that uses the genetic distances of these genes for species demarcation.

Incidence and transmission of a granulovirus in a large codling moth [Cydia pomonella L. (Lepidoptera: Tortricidae)] rearing facility

Incidences of potential per os Cydia pomonella granulovirus (CpGV) transmission within a large codling moth colony were identified. CpGV was detected in the water which is used to wash egg sheets. When pre-neonates were extracted from eggs prior to emergence and tested for the presence of CpGV, 40% were found to carry amounts of CpGV detectable by a polymerase chain reaction (PCR) assay, suggesting possible transovarial transmission of the virus. Although symptoms typical of virus infection and larval death were found infrequently within communal rearing trays, the frequency with which CpGV DNA was detected by PCR assays increased from a mean of 31% of 10-day-old larvae to 94% of 25-day-old larvae. CpGV in codling moth cadavers remained virulent after being held at 60 degrees C for 3 days under conditions similar to the treatment of spent diet at the rearing facility before its disposal. PCR tests of surface samples taken from air filters and rearing rooms of the rearing facility were found to contain CpGV. Bioassays of surface samples from the diet trash bin and a filter through which outside air is passed before entering the rearing chambers resulted in significant codling moth neonate mortality. The virulence of CpGV in dust from the spent diet and the original inadvertent positioning of the diet trash bin directly below one of the air intake ducts are suggested as a possible additional source of CpGV contamination within the facility.

Characterization of Ha29, a specific gene for Helicoverpa armigera single-nucleocapsid nucleopolyhedrovirus

Open reading frame 29 (ha29) is a gene specific for Helicoverpa armigera single-nucleocapsid nucleopolyhedrovirus (HearSNPV). Sequence analyses showed that the transcription factor Tfb2 motif, bromodomain and Half-A-TPR (HAT) repeat were present at aa 66-82, 4-76, 55-90 of the Ha29 protein respectively. The product of Ha29 was detected in HearSNPV-infected HzAM1 cells at 3 h post-infection. Western blot analysis using a polyclonal antibody produced by immunizing a rabbit with purified GST-Ha29 fusion protein indicates that Ha29 is an early gene. The size of Ha29 product in infected HzAM1 cells was about 25 kDa, which was larger than the presumed size of 20.4 kDa. Tunicamycin treatment of HearSNPV-infected HzAM1 cells suggested that the Ha29 protein is N-glycosylated. Fluorescent confocal laser scanning microscope examination, and Western blot analysis of purified budded virus (BVs), occlusion-derived virus (ODVs), cell nuclear and cytoplasmic fraction, showed that the Ha29 protein was localized in the nucleus. Our results suggested that ha29 of HearSNPV encodes a non-structurally functional protein that may be associated with virus gene transcription in Helicoverpa hosts.

A cellular Drosophila melanogaster protein with similarity to baculovirus F envelope fusion proteins

Baculovirus F (fusion) proteins are found in the envelopes of budded virions. Recently a Drosophila melanogaster gene (CG4715) that encodes a protein with sequence similarity to baculovirus F proteins was discovered. To examine similarities and differences with baculovirus F proteins, we cloned the D. melanogaster cellular F (Dm-cF) protein gene and analyzed Dm-cF expression and localization. The predicted Dm-cF protein sequence lacks a furin cleavage site, and transiently expressed Dm-cF showed no protein cleavage and no detectable membrane fusion activity. In cell localization studies, transiently expressed Dm-cF was localized to intracellular organelles in D. melanogaster S2 cells, unlike baculovirus F proteins, which localize to cellular plasma membranes. Using reverse transcriptase PCR and Western blot analysis to examine Dm-cF expression in animals, we detected Dm-cF expression in both larval and adult D. melanogaster cells. However, Dm-cF expression was detected only in third instar larvae and adults, suggesting that Dm-cF expression may be developmentally regulated. We also identified genes related to Dm-cF in the genomes of two other Drosophila species, Drosophila yakuba and Drosophila pseudoobscura, and the mosquito Anopheles gambiae. These observations suggest that f genes may be present in the genomes of many insects. Conservation within and between 22 baculovirus and 4 insect F proteins was examined in detail. These studies demonstrate that Dm-cF is expressed in D. melanogaster and suggest that if baculovirus f genes are derived from a host cellular f gene, the function appears to have changed substantially upon adaptation to the baculovirus infection cycle.

Characterization of a late expression gene, Open reading frame 128 of Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus

Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus (HearSNPV) is a single embedded NPV pathogenic to the bollworm, which is a major agricultural pest in many areas around the world. Ha128 homologues have been identified in all completely sequenced lepidopteran NPV's, but no homologue has been found in a granulovirus (GV) and it is thus considered as a lepidopteran NPV-specific gene. In the HearSNPV-C1 genome Ha128 is located between 120,252 and 121,052 bp and encodes a putative protein of 266 amino acid residues with a predicted molecular weight of 30.5 kDa. Ha128 transcripts in HearSNPV-infected HzAM1 cells could be detected from 24 to 120 h post-infection (p.i.) by Northern blot. The Ha128 protein was detected at 24 h p.i. and remained detectable until 120 h p.i. by western blot using an anti-GST-Ha128 antiserum. The expression of Ha128 was inhibited in the presence of Ara-C, an inhibitor of viral DNA synthesis. These results together indicated that Ha128 was a late gene. The product of Ha128 was found to have an Mr of about 31 kDa, in agreement with the predicted molecular weight. Immunoflorescence using anti-GST-Ha128 serum showed that Ha128 was located in cytoplasm. GST pull-down and co-immunoprecipitation showed that at least two potential host proteins interacted with Ha128. In conclusion, Ha128 is a late protein localized in the cytoplasm of infected cells that may interact with host proteins.