RESULTS:
1 - 5 of 5 for "Jean-Michel Drezen"
Transcriptional dynamics during Heliothis zea nudivirus 1 infection in an ovarian cell line from Helicoverpa zea
Nudiviruses (family Nudiviridae) are double-stranded DNA viruses that infect various insects and crustaceans. Among them Heliothis zea nudivirus 1 (HzNV-1) represents the rare case of a lepidopteran nudivirus inducing a sexual pathology. Studies about molecular pathological dynamics of HzNV-1 or other nudiviruses are scarce. Hence this study aims to provide a transcriptomic profile of HzNV-1 in an ovary-derived cell line of Helicoverpa zea (HZ-AM1) during early (3 6 and 9 h post-infection) and advanced (12 and 24 h post-infection) stages of infection. Total RNA was extracted from both virus- and mock-infected cells and RNA-seq analysis was performed to examine both virus and host transcriptional dynamics. Hierarchical clustering was used to categorize viral genes while differential gene expression analysis was utilized to pinpoint host genes that are significantly affected by the infection. Hierarchical clustering classified the 154 HzNV-1 genes into four temporal phases with early phases mainly involving transcription and replication genes and later phases including genes for virion assembly. In addition a novel viral promoter motif was identified in the upstream region of early-expressed genes. Host gene analysis revealed significant upregulation of heat shock protein genes and downregulation of histone genes. The identification of temporal patterns in viral gene expression enhances the molecular understanding of nudivirus pathology while the identified differentially expressed host genes highlight the key pathways most hijacked by HzNV-1 infection.
Chelonus inanitus bracovirus encodes lineage-specific proteins and truncated immune IκB-like factors
Bracoviruses and ichnoviruses are endogenous viruses of parasitic wasps that produce particles containing virulence genes expressed in host tissues and necessary for parasitism success. In the case of bracoviruses the particles are produced by conserved genes of nudiviral origin integrated permanently in the wasp genome whereas the virulence genes can strikingly differ depending on the wasp lineage. To date most data obtained on bracoviruses concerned species from the braconid subfamily of Microgastrinae. To gain a broader view on the diversity of virulence genes we sequenced the genome packaged in the particles of Chelonus inanitus bracovirus (CiBV) produced by a wasp belonging to a different subfamily: the Cheloninae. These are egg-larval parasitoids which means that they oviposit into the host egg and the wasp larvae then develop within the larval stages of the host. We found that most of CiBV virulence genes belong to families that are specific to Cheloninae. As other bracoviruses and ichnoviruses however CiBV encode v-ank genes encoding truncated versions of the immune cactus/IκB factor which suggests these proteins might play a key role in host–parasite interactions involving domesticated endogenous viruses. We found that the structures of CiBV V-ANKs are different from those previously reported. Phylogenetic analysis supports the hypothesis that they may originate from a cactus/IκB immune gene from the wasp genome acquired by the bracovirus. However their evolutionary history is different from that shared by other V-ANKs whose common origin probably reflects horizontal gene transfer events of virus sequences between braconid and ichneumonid wasps.
Identification of bracovirus particle proteins and analysis of their transcript levels at the stage of virion formation
Polydnaviruses (PDVs) are unique symbiotic viruses associated with parasitic wasps; they replicate only in the calyx cells of a wasp's ovaries and are transferred at oviposition along with the parasitoid egg into the lepidopteran host. The DNA packaged in the viral particles encodes factors that manipulate the host's immune defences and development to benefit the parasitoid. PDVs are found in two subfamilies of ichneumonids (ichnoviruses) and in braconids of the microgastroid complex (bracoviruses). We recently showed that the latter derive from an ancestral nudivirus as 24 nudivirus-related genes were identified in ovaries of two distantly related braconids at the stage of virion formation. Here we present a comprehensive analysis of the viral particle proteins of the Chelonus inanitus bracovirus (CiBV). Proteins of purified CiBV particles were analysed by mass spectrometry and amino acid sequences matched to the existing ovarian-cDNA database. In addition transcript quantities of identified genes were measured by quantitative real-time PCR in female pupae at the onset and peak of virion formation and at corresponding stages in male pupae. This combined approach allowed the identification of 44 CiBV particle proteins: 16 were nudivirus-related three had similarity to ovarian proteins of another braconid 11 had similarity to cellular proteins and 14 had no similarity to known proteins. The transcripts of all of them increased in female but not male pupae. These data confirm the important contribution of nudivirus genes but also indicate the presence of many lineage- or species-specific proteins possibly involved in the parasitoid–host interaction.
Characterization of the IκB-like gene family in polydnaviruses associated with wasps belonging to different Braconid subfamilies
Polydnaviruses (PDVs) are obligate symbionts of hymenopteran parasitoids of lepidopteran larvae that induce host immunosuppression and physiological redirection. PDVs include bracoviruses (BVs) and ichnoviruses (IVs) which are associated with braconid and ichneumonid wasps respectively. In this study the gene family encoding IκB-like proteins in the BVs associated with Cotesia congregata (CcBV) and Toxoneuron nigriceps (TnBV) was analysed. PDV-encoded IκB-like proteins (ANK) are similar to insect and mammalian IκB an inhibitor of the transcription factor nuclear factor κB (NF-κB) but display shorter ankyrin domains and lack the regulatory domains for signal-mediated degradation and turnover. Phylogenetic analysis of ANK proteins indicates that those of IVs and BVs are closely related even though these two taxa are believed to lack a common ancestor. Starting from a few hours after parasitization the transcripts of BV ank genes were detected at different levels in several host tissues. The structure of the predicted proteins suggests that they may stably bind NF-κB/Rel transcription factors of the tumour necrosis factor (TNF)/Toll immune pathway. Accordingly after bacterial challenge of Heliothis virescens host larvae parasitized by T. nigriceps NF-κB immunoreactive material failed to enter the nucleus of host haemocytes and fat body cells. Moreover transfection experiments in human HeLa cells demonstrated that a TnBV ank1 gene product reduced the efficiency of the TNF-α-induced expression of a reporter gene under NF-κB transcriptional control. Altogether these results suggest strongly that TnBV ANK proteins cause retention of NF-κB/Rel factors in the cytoplasm and may thus contribute to suppression of the immune response in parasitized host larvae.
Excision of the polydnavirus chromosomal integrated EP1 sequence of the parasitoid wasp Cotesia congregata (Braconidae, Microgastinae) at potential recombinase binding sites
Cotesia congregata polydnavirus (CcPDV) is essential for successful parasitism of Manduca sexta larvae by the braconid wasp Cotesia congregata. To determine the molecular mechanisms for the vertical transmission of CcPDV in the wasps we analysed the different forms of the virus sequences containing the gene encoding the early parasitism-specific protein 1 (EP1). By a detailed molecular analysis we demonstrated that the EP1 sequences are present in wasp DNA in two forms: a circular form as seen in the virus particles and a form integrated into the wasp genome. Moreover we showed that the integrated form of the EP1 sequences is able to excise in the ovary cells. A fragment corresponding to an EP1 ‘empty locus’(without the viral sequence) was PCR-amplified from ovarian DNA. Comparison of the sequences isolated from the EP1 circle the integrated form and the empty locus revealed that the extremities of the EP1 genomic sequences constitute a direct repeat. Strikingly these sequences contain a potential binding site for a recombinase of the Hin family located in close vicinity to the position where the DNA strand exchange occurs. Thus the data bear upon the possibility that the bracovirus circles are excised via a mechanism related to the Hin mediated Conservative Specific-Specific Recombination (CSSR) of prokaryotes.