Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Polydnaviridae”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed2006

Unfolding the evolutionary story of polydnaviruses.

Polydnaviruses (PDVs) are fascinating viruses. Described in thousands of parasitoid wasp species they are unique viruses having both a segmented DNA genome in viral particles and an integrated form that persists as a provirus in the wasp genome. Parasitoid wasps inject their eggs in another insect host typically a lepidopteran. In these host-parasitoid interactions, the virus particles are co-injected along with the eggs and are essential to ensure wasp parasitism success. PDVs do not replicate in the lepidopteran host, but expression of viral gene products confers protection from the host immune defence response. Two genera of PDVs phylogenetically unrelated exist, the bracoviruses (BVs) and the ichnoviruses (IVs), associated with braconid and ichneumonid wasps, respectively. New data on the genomes of two bracoviruses (Microplitis demolitor BV and Cotesia congregata BV) and an ichnovirus associated with Campoletis sonorensis (CsIV) offers us new elements to discuss the central questions concerning the origin of these viral entities and how they have evolved. The results of sequencing approaches indicate that the tens of millions of years of mutualistic associations between PDVs and wasps have had a strong impact on PDV genomes that now ressemble eukaryotic regions both in organization and gene content.

Animals↗
PubMed2003

Persistence and expression of Cotesia congregata polydnavirus in host larvae of the tobacco hornworm, Manduca sexta.

The gregarious braconid wasp Cotesia congregata parasitizes host larvae of Manduca sexta, and several other sphingid species. Parasitism induces host immunosuppression due to the disruptive action of the wasp's polydnavirus (PDV) on host blood cells. During the initial stages of parasitism, these cells undergo apoptosis followed by cell clumping, which clears the hemolymph of a large number of cells. In this study, the persistence and expression of Cotesia congregata PDV (CcPDV) were examined using Southern and Northern blots, respectively. Digoxygenin-labelled total polydnaviral DNA was used to probe genomic DNA isolated from fat body and brains of hosts with emerged wasps taken 6 days following egress of the parasitoids, and significant cross-hybridization between the host fat body genomic DNA with viral DNA was seen. Thus, the virus persists in the host for the duration of parasitism, even during the post-emergence period, and may even be integrated in the host caterpillar DNA. Viral gene expression was examined using Northern blots and probes to the Cotesia rubecula CrV1 homolog, and the CrV1-like mRNAs were expressed as early as 4 h post-parasitization for at least 72 h and faint hybrization is even seen at the time the wasps eclose. In contrast, in Pieris rapae larvae the CrV1 transcript is expressed only for a brief time, during which time hemocyte function is disrupted. The effect is transitory, and hemocytes regain their normal functions after the parasites emerge as first instars.The genome of CcPDV contains one copy of the CrV1-like homolog as shown on Southern blots of viral genomic DNA. In conjunction with our earlier studies of the PDV-encoded early protein 1, the current work suggests multiple viral transcripts are produced following parasitization of the host, and likely target host hemocytes to induce their apoptosis, thereby preventing encapsulation of the parasitoid's eggs. Whether viral DNAs are integrated in the host's genomic DNA remains to be proven, but our results provide preliminary evidence that viral DNAs are detected in the host's fat body cells examined at the time of wasp emergence and several days later.

Animals↗
PubMed2003

Characterization of Campoletis sonorensis ichnovirus unique segment B and excision locus structure.

Polydnaviruses (PDVs) are segmented, symbiotic, double-stranded DNA viruses that are vertically transmitted as proviruses within the genomes of some parasitoid Hymenoptera. The PDV associated with the ichneumonid wasp Campoletis sonorensis (CsIV) consists of 24 non-redundant DNA segments varying in size from approximately 6 to 20 kbp. CsIV segment B, one of the smallest genome segments, was sequenced and the excision sites of the proviral segment were characterized. The segment B sequence was 83.2% non-coding with only two open reading frames (ORFs). Some non-coding sequences have similarities to database sequences and were likely pseudogenic, but most were unrelated to known nucleic acid or predicted protein sequences. One ORF, BHv0.9, encodes a member of the rep gene family and was expressed only in parasitized insects while transcription of the other ORF could not be detected. Previously, a third region of the segment was shown to hybridize to 0.6 and 1.2 kb poly A+ RNAs from female wasps during virus replication (Theilmann and Summers, 1988) but this region did not have an identifiable ORF in the determined sequence. In contrast to CsIV segment W, segment B had little repetitive sequence. The segment B proviral integration locus contains a 59 bp direct imperfect repeat. Further analyses of this integration locus demonstrated that segment B was excised from wasp genomic DNA with flanking sequences at the integration site rejoined after segment excision. The segment B "excision locus" retained one of the two copies of the 59 bp repeat sequence with the other repeat present in the excised segment. The data indicate that Ichnovirus segments have distinctive characteristics possibly reflecting functional co-evolution between the wasp and individual types of polydnavirus segments.

Animals↗
PubMed2003

Active suppression of D. melanogaster immune response by long gland products of the parasitic wasp Leptopilina boulardi.

To develop inside their insect hosts, endoparasitoid wasps must either evade or overcome the host's immune system. Several ichneumonid and braconid wasps inject polydnaviruses that display well-studied immune suppressive effects. However, little is known about the strategies of immunoevasion used by other parasitoid families, such as figitid wasps. The present study provides experimental evidence, based on superparasitism and injection experiments, that the figitid species Leptopilina boulardi uses an active mechanism to suppress the Drosophila melanogaster host immune response, i.e. the encapsulation of the parasitoid eggs. The immune suppressive factors are localised in the long gland and reservoir of the female genital tractus, where virus-like particles (VLPs) have been observed. Parasitism experiments using a host tumorous strain indicate that these factors do not destroy host lamellocytes but that they impair the melanisation pathway. Interestingly, they are not susceptible to heating and are not depleted with prolonged oviposition experience, in contrast to observations reported for L. heterotoma, another figitid species. The mechanisms that prevent encapsulation of eggs from L. boulardi and L. heterotoma differ in several respects, suggesting that different physiological strategies of immunosuppression might be used by specialised and generalist parasitoids.

Animals↗
PubMed2003

Three related TrIV genes: comparative sequence analysis and expression in host larvae and Cf-124T cells.

We report on the cloning and sequencing of two Tranosema rostrale ichnovirus (TrIV) genes, and assess their relatedness to TrV1, the gene encoding the most abundant TrIV transcript in last-instar Choristoneura fumiferana larvae parasitized by T. rostrale. One of the two newly isolated genes, TrV2, features an organization similar to that of TrV1, with one intron flanked by two exons; it encodes a 102 amino acid protein showing 79% similarity to TrV1. The third gene, TrV4, encodes a larger protein (143 aa) displaying similarity to the other two only over the first approximately 50 amino acid residues of its sequence; the remaining portion contains an imperfect octad repeat. Although the TrV4 gene contains only one exon, it has an intron similar in size and sequence to that of TrV1 and TrV2; in fact, the non-coding regions of all three genes show higher sequence identity than the coding regions, pointing to their common origin. Southern analysis suggests that each gene maps to a different TrIV genome segment, with homologous sequences apparently present on other segments. TrV1 and TrV4 transcription in penultimate (5th) instar hosts, parasitized shortly after the molt, was strong for both genes 1 and 2 days p.p., with transcript abundance decreasing after the final molt; thus, neither of these genes is upregulated during induction of developmental arrest in last-instar hosts. Cf-124T cells inoculated with T. rostrale calyx fluid showed significant levels of apoptosis 24-72 h p.i.; TrV1 was detected in the culture medium, suggesting that this and/or other TrIV-encoded proteins may be responsible for the observed cytopathic effect. Southern and Northern analyses, using DNA and RNA extracted from infected Cf-124T cells, revealed the presence of both TrV1- and TrV4-carrying genome segments and transcripts, but neither DNA, at least in episomal form, nor mRNA persisted for more than a few days p.i. This in vitro system may provide a suitable starting point for the study of TrIV gene functions.

Amino Acid Sequence↗
PubMed2003

Virus or not? Phylogenetics of polydnaviruses and their wasp carriers.

Our current, still limited, understanding of the comparative biology and evolution of polydnaviruses (PDVs) is reviewed, especially in the context of the possible origins of these parasitoid viruses and of their coevolution with carrier wasps. A hypothetical scenario of evolution of PDVs from ascovirus (or ascovirus-like) ancestors is presented, with examples of apparent extant transitional forms. PDVs appear, in the case of bracoviruses, to show phylogenetic relationships that mirror those of their wasp carriers: with ichnoviruses, the picture is less clear. Ongoing sequencing studies of entire PDV genomes from diverse wasp species are likely to greatly contribute to our understanding of PDV evolution.

Animals↗
PubMed2003

Polydnavirus genome: integrated vs. free virus.

Polydnaviruses are unique because of their obligatory association with thousands of parasitoid wasp species from the braconid and ichneumonid families of hymenopterans. PDVs are injected into the parasitized hosts and are essential for parasitism success. However, polydnaviruses are also unique because of their genome composed of multiple dsDNA segments. Cytological evidence has recently confirmed the results of genetic and molecular analyses indicating that PDV segments were integrated in the wasp genome. Moreover a phylogenetic study performed using the age of available fossils to calibrate the molecular clock indicated that the polydnaviruses harboured by braconid wasps have resided within the wasp genome for approximately 70 million years. In the absence of horizontal transmission, the evolution of the PDV genomes has been driven exclusively by the reproductive success they have offered the wasps. The consequences of this particular selection pressure can be observed in the gene content of certain PDV genomes from which increasing sequence data are available. Molecular mechanisms already identified could be involved in the acquisition and loss of genes by the PDV genomes and lead us to speculate on the definition of the virus genome.

Biological Evolution↗
PubMed2003

Expression of Cotesia kariyai polydnavirus genes in lepidopteran hemocytes and Sf9 cells.

The parasitic wasp Cotesia kariyai carries polydnavirus (CkPDV) which is an indispensable factor for the successful parasitization by the wasp. One of its surface proteins has been identified as an immunoevasive mediator from the cellular defense reactions of the host armyworm Pseudaletia separata, thereby it was named immunoevasive protein (IEP). In the present study, we demonstrated that anti-IEP antibody did not suppress the CkPDV infection of Sf9 cells but decreased its infection of P.separata hemocytes, thus indicating that IEP is not essential for CkPDV to enter into the target cells but is important for evading from the attack of the hemocytes. Three genes of CkPDV expressed in Sf9 cells were isolated and characterized. Two of them (CkV0.8, CkV0.9) are novel genes but another one (CkV2.0) is the same gene with the one we previously identified in the parasitized armyworm larvae. Although these genes reside in different DNA segments of CkPDV genome, all of them are expressed in the hemocytes of the parasitized armyworm larvae. These gene transcripts are first detected at 2 h after parasitization, and the expressions of CkV0.8 and CkV0.9 were gradually decreased after reaching the maximum level at 4 h after parasitization. However, the expression of CkV2.0 continues to be increased at least for 10 h after parasitization.

Amino Acid Sequence↗
PubMed2003

Two Hyposoter didmator ichnovirus genes expressed in the lepidopteran host encode secreted or membrane-associated serine and threonine rich proteins in segments that may be nested.

We present in this work two novel Hyposoter didymator ichnovirus genes expressed in parasitized Spodoptera larvae. These genes, named HdCorfS6 and HdGorfP30, are unrelated and present in two different genome segments, possibly nested, SH-C and SH-G respectively. HdCorfS6 encodes a predicted transmembrane protein, putatively glycosylated. HdCorfS6 transcripts appear to be abundant in lepidopteran host hemocytes compared to the other tissues analyzed. The second gene described, HdGorfP30, is well expressed in hemocytes, but also in other tissues, such as the fat body, nervous system and epidermis. This gene is peculiar since it presents 17 perfectly conserved repeated sequences arranged in tandem arrays. Each of these repeats contains 58% of serine and threonine residues and therefore several potential sites for glycosylation. This mucin-like protein, predicted as highly glycosylated, could be involved in host immune suppression.

Amino Acid Sequence↗
PubMed2003

Polydnavirus integration in lepidopteran host cells in vitro.

The long-term persistence of polydnavirus (PDV) DNA in infected lepidopteran cell cultures has suggested that at least some of the virus sequences become integrated permanently into the cell genome. In the current study, we provide supportive evidence of this event. Cloned libraries were prepared from two different Lymantria dispar (gypsy moth) cell lines that had been maintained in continuous culture for more than five years after infection with Glyptapanteles indiensis PDV (GiPDV). Junction clones containing both insect chromosomal and polydnaviral sequences were isolated. Precise integration junction sites were identified by sequence comparison of linear (integrated) and circular forms of the GiPDV genome segment F, from which viral sequences originated. Host chromosomal sequences at the site of integration varied between the two L. dispar cell lines but virus sequence junctions were identical and contained a 4-base pair CATG palindromic repeat. The GiPDV segment F does not encode any self-replication or self-insertion proteins, suggesting a host-derived mechanism is responsible for its in vitro integration. The chromosomal site of one junction clone contained sequences indicative of a new L. dispar retrotransposon, including a putative reverse transcriptase and integrase located upstream of the site of viral integration. A potential mechanism is proposed for the integration of PDV DNA in vitro. It remains to be seen if integration of the virus also occurs in the lepidopteran host in vivo.

Amino Acid Sequence↗
PubMed2003

Similar polydnavirus genes of two parasitoids, Cotesia kariyai and Cotesia ruficrus, of the host Pseudaletia separata.

Endoparasitoids can achieve successful development in suitable hosts with the help of polydnavirus (PDV), if it is injected into the host with their eggs at parasitization. It was predicted that different species of endoparasitoids that parasitize the same host successfully use a similar system to avoid the defense reaction from the host. In this study, we identified similar PDVs genes. In two endoparasitoids, Cotesia kariyai (Cky) and Cotesia ruficrus (Crf), which can parasitize the same host species, Pseudaletia separata. The electrophoretic profiles of nondigestive segments of PDV in the two parasitoids were different. However, genomic Southern hybridization using reciprocal probes between the two species indicated a similar sequence of PDV genes. Two cDNA libraries were established and screened by a Cky probe. Cky811 was 695-bp, Crf111 was 690-bp, and the predicted peptide sequences were 162aa and 157aa, respectively. The two transcripts had 72.8% similarity with each other and resembled a C-type lectin2 domain. Clones of Cky811 from C. kariyai and Crf111 from C. ruficrus were expressed in hemocytes of the hosts that were injected with PDV plus venom. The Cky811 gene was expressed in hemocytes and fat body of the Pseudaletia host. Hybridization analysis revealed that the Cky811 gene was expressed 6 hrs after injection of Cky-PDV into nonparasitized hosts with venom, and the hybridization signal declined with time. The genetic distance to the lectin of other insects was closer to P. americana than to Lepidopteran insects.

Amino Acid Sequence↗
PubMed2003

Cross-protection experiments with parasitoids in the genus Microplitis (Hymenoptera: Braconidae) suggest a high level of specificity in their associated bracoviruses.

The immunological and developmental effects of bracoviruses (BVs) from three parasitoids in the genus Microplitis (Braconidae: Microgastrinae) were compared in the hosts Pseudoplusia includens and Heliothis virescens (Lepidoptera: Noctuidae). Southern blotting experiments indicated that viral DNAs from Microplitis demolitor bracovirus (MdBV) cross-hybridized with viral DNAs from Microplitis croceipes bracovirus (McBV) and Microplitis mediator bracovirus (MmBV) under conditions of high stringency. Injection of calyx fluid plus venom from each parasitoid species dose-dependently delayed development of P. includens and H. virescens. Each virus also inhibited pupation of P. includens but not H. virescens. In situ hybridization experiments indicated that MdBV and McBV persistently infect hemocytes in both hosts while MmBV persistently infects hemocytes in P. includens but not H. virescens. While MdBV infection induced a loss of adhesion by most plasmatocytes, McBV and MmBV infection induced a loss of adhesion in less than 50% of cells. Cross-protection experiments indicated that calyx fluid plus venom from one species usually protected progeny of another species from encapsulation but did not always promote successful development.

Animals↗
PubMed2006

Polydnavirus genes that enhance the baculovirus expression vector system.

The baculovirus expression vector system (BEVS) is a powerful and versatile system for protein expression, which has many advantages. However, a limitation of any lytic viral expression system, including BEVS, is that death and lysis of infected insect cells terminates protein production. This results in interruption of protein production and higher production costs due to the need to set up new infections, maintain uninfected cells, and produce pure viral stocks. Genetic methods to slow or prevent cell death while maintaining high-level, virus-driven protein production could dramatically increase protein yields. Several approaches have been used to improve the BEVS and increase the synthesis of functional proteins. Successful enhancement of the BEVS was obtained when various gene elements were added to the virus, secretion and posttranslational processing were modified, or protein integrity was improved. A gene family from the insect virus Campoletis sonorensis ichnovirus (CsIV) was discovered that delays lysis of baculovirus-infected cells, thereby significantly enhancing recombinant protein production in the BEVS system. By using the CsIV vankyrin gene family, protein production in the vankyrin-enhanced BEVS (VE-BEVS) was increased by a factor of 4- to 15-fold by either coexpressing the vankyrin protein from a dual BEVS or by providing its activity in trans by expressing the vankyrin protein from a stably transformed cell line. In sum, VE-BEVS is an enhancement of the existing BEVS technology that markedly improves protein expression levels while reducing the cost of labor and materials.

Amino Acid Sequence↗
PubMed2006

Potential uses of Cys-motif and other polydnavirus genes in biotechnology.

Exploiting the ability of insect pathogens, parasites, and predators to control natural and damaging insect populations is a cornerstone of biological control. Here we focus on an unusual group of viruses, the polydnaviruses (PDV), which are obligate symbionts of some hymenopteran insect parasitoids. PDVs have a variety of important pathogenic effects on their parasitized hosts. The genes controlling some of these pathogenic effects, such as inhibition of host development, induction of precocious metamorphosis, slowed or reduced feeding, and immune suppression, may have use for biotechnological applications. In this chapter, we consider the physiological functions of both wasp and viral genes with emphasis on the Cys-motif gene family and their potential use for insect pest control.

Animals↗
PubMed2000

Evidence for integration of Glyptapanteles indiensis polydnavirus DNA into the chromosome of Lymantria dispar in vitro.

Polydnaviruses replicate within calyx cells of the female ovaries of certain species of parasitic wasps and are required for the successful parasitization of lepidopteran hosts. These viruses, which have unusual double-stranded circular DNA segmented genomes, are integrated as proviruses into the genomes of their associated wasp hosts and are believed to be transmitted vertically through germline tissue. Here, by combined Southern hybridization, polymerase chain reaction (PCR) assays and viral sequence analyses we provide evidence that DNA originating from two distinct double-stranded circular segments of the polydnavirus genome from the braconid Glyptapanteles indiensis (GiPDV) integrates in vitro into the genome of cells derived from the natural host, Lymantria dispar. The G. indiensis polydnavirus DNA, as a result of its unique ability to be integrated in part into the chromosome of cells derived from its lepidopteran host, has potential to be developed as an in vitro cell transformation system.

Animals↗
PubMed2002

A coiled-coil region of an insect immune suppressor protein is involved in binding and uptake by hemocytes.

Polydnaviruses are associated with certain parasitoid wasps and are introduced into the body cavity of the host caterpillar during oviposition. Some of the viral genes are expressed in host tissues and corresponding proteins are secreted into the hemocoel causing suppression of the host immune system. The Cotesia rubecula polydnavirus gene product, CrV1, effectively inactivates hemocytes by mediating cytoskeleton breakdown. A precondition for the CrV1 function is the incorporation of the extracellular protein by hemocytes. Here, we show that a coiled-coil domain containing a putative leucine zipper is required for CrV1 function, since removal of this domain abolishes binding and uptake of the CrV1 protein by hemocytes.

Amino Acid Sequence↗
PubMed1997

Purification and analysis of a polydnavirus gene product expressed using a poly-histidine baculovirus vector.

The VHv1.1 polydnavirus gene has been implicated in suppressing the encapsulation response in parasitized insects [Li and Webb (1994) J. Virol. 68, 7482-7489]. In order to characterize this gene product and to further our analysis of its immunosuppressive function, we expressed the VHv1.1 using a custom-designed C-terminal poly-histidine baculovirus vector which allows for high expression and single-step purification of the protein. The 34 kDa VHv1.1 protein was expressed in baculovirus-infected cell cultures and in H. virescens larvae. Highly enriched preparations of the secreted VHv1.1 protein were obtained after affinity chromatography using a NTA-(Ni2+) resin. Characterization with purified preparations of the VHv1.1 protein established that the protein is N-glycosylated, containing glycogroups which are PNGase F-sensitive but Endo H-resistant. The recombinant VHv1.1 protein bound to hemocytes in vitro and in vivo and was endocytosed in a manner similar to the native protein produced in CsPDV-infected larvae.

Animals↗