Characterization and biochemical analyses of venom from the ectoparasitic wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae)

Amount of venom that Leptopilina species inject into Drosophila melanogaster larvae in relation to parasitic success

The Drosophila endoparasitoid wasps Leptopilina boulardi and L. heterotoma (Hymenoptera: Cynipidae) are pro-ovigenic species, i.e., females contain their lifetime number of mature eggs at emergence. They are therefore able to immediately parasitize many hosts when present. In response to parasitoid oviposition, the larval host D. melanogaster can mount an immune response, encapsulation, that can destroy the parasitoid eggs. This response is counteracted by the venom the wasp injects during oviposition. Here, we estimated the amount of venom injected into a D. melanogaster host larva using immunodetection of venom proteins and we attempted to correlate this amount with the number of eggs a female can lay on successive days. The venom reservoir of L. boulardi contains enough venom for at least 100 ovipositions while that of L. heterotoma contains venom for about 16 ovipositions. While a female L. boulardi may have enough venom for three days of parasitism when 20 or 40 larval hosts were presented each day, L. heterotoma certainly needs to synthesize new venom to parasitize the number of hosts offered. Interestingly, parasitism stopped (L. boulardi), egg protection (L. heterotoma) and egg hatching decreased (both species) after three days of parasitism. Thus, although venom does not appear to be a limiting factor for parasitism, our data suggest that it may have less effectiveness on the egg protection and on egg/host development after high repetitive egg laying.

A new approach for investigating venom function applied to venom calreticulin in a parasitoid wasp

A new method is developed to investigate functions of venom components, using venom gene RNA interference knockdown in the venomous animal coupled with RNA sequencing in the envenomated host animal. The vRNAi/eRNA-Seq approach is applied to the venom calreticulin component (v-crc) of the parasitoid wasp Nasonia vitripennis. Parasitoids are common, venomous animals that inject venom proteins into host insects, where they modulate physiology and metabolism to produce a better food resource for the parasitoid larvae. vRNAi/eRNA-Seq indicates that v-crc acts to suppress expression of innate immune cell response, enhance expression of clotting genes in the host, and up-regulate cuticle genes. V-crc KD also results in an increased melanization reaction immediately following envenomation. We propose that v-crc inhibits innate immune response to parasitoid venom and reduces host bleeding during adult and larval parasitoid feeding. Experiments do not support the hypothesis that v-crc is required for the developmental arrest phenotype observed in envenomated hosts. We propose that an important role for some venom components is to reduce (modulate) the exaggerated effects of other venom components on target host gene expression, physiology, and survival, and term this venom mitigation. A model is developed that uses vRNAi/eRNA-Seq to quantify the contribution of individual venom components to total venom phenotypes, and to define different categories of mitigation by individual venoms on host gene expression. Mitigating functions likely contribute to the diversity of venom proteins in parasitoids and other venomous organisms.

The role of serine- and metalloproteases in Nasonia vitripennis venom in cell death related processes towards a Spodoptera frugiperda Sf21 cell line

Proteases are predominant venom components of the ectoparasitoid Nasonia vitripennis. Two protease families, serine proteases and metalloproteases were examined for their possible cytotoxic functions in the Spodoptera frugiperda (Sf21) cell line using protease inhibitors that inactivate one or both protease families. Viability assays on adherent cells indicated that both protease families are among the main cytotoxic compounds of N. vitripennis venom. However, viability assays and flow cytometry performed on suspension cells 24h after envenomation revealed that inactivation of metalloproteases did not improve cell survival. These results indicate that both protease families may have tissue specific functions. Time course experiments indicate that serine proteases of N. vitripennis venom are responsible for inducing apoptosis in the Sf21 cell line. However, other venom compounds could also be involved in this process and different cell death pathways may take over when a specific type of cell death is inhibited. During parasitation of their natural hosts, both protease families may possibly function in immune related processes and tissue destruction, enabling venom distribution. Overall, this study provides important insights into the functions of serine and metalloproteases in the venom of N. vitripennis.

"It stings a bit but it cleans well": venoms of Hymenoptera and their antimicrobial potential

Venoms from Hymenoptera display a wide range of functions and biological roles. These notably include manipulation of the host, capture of prey and defense against competitors and predators thanks to endocrine and immune systems disruptors, neurotoxic, cytolytic and pain-inducing venom components. Recent works indicate that many hymenopteran species, whatever their life style, have also evolved a venom with properties which enable it to regulate microbial infections, both in stinging and stung animals. In contrast to biting insects and their salivary glands, stinging Hymenoptera seem to constitute an under-exploited ecological niche for agents of vector-borne disease. Few parasitic or mutualistic microorganisms have been reported to be hosted by venom-producing organs or to be transmitted to stung animals. This may result from the presence of potent antimicrobial molecules in venoms, histological features of venom apparatuses and selective effects of venoms on immune defenses of targeted organisms. The present paper reviews for the first time the venom antimicrobial potential of solitary and social Hymenoptera in molecular, ecological, and evolutionary perspectives.

Pathological and ultrastructural changes in cultured cells induced by venom from the ectoparasitic wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae)

The ectoparasitic wasp Nasonia vitripennis produces a proteinaceous venom that induces death in fly hosts by non-paralytic mechanisms. Previous in vitro assays have suggested that the primary cause of cell and tissue death is oncosis, a non-programmed cell death (PCD) pathway characterized by cellular swelling and lysis. However, ultrastructural analyses of BTI-TN-5B1 cells exposed to LC(99) doses of wasp venom revealed cellular changes more consistent with apoptosis and/or non-apoptotic PCD than oncosis or necrosis: By 3h after incubation with venom, susceptible cells displayed indentations in the nuclear membranes, large nucleoli, and extensive vacuolization throughout the cytoplasm. In the vast majority of venom treated cells, annexin V bound to the plasma membrane surface within 15 min after treatment, a characteristic consistent with translocation of phosphatidylserine to the cell surface during the early stages of apoptosis. Likewise, mitochondrial transmembrane potential was depressed in cells within 15 min in venom-treated cells, an event that occurred in the absence of mitochondrial swelling or rupturing of cristae. Active caspase 3 was detected by fluorescent labeling in nearly all venom treated cells 3h after exposure to venom, and in turn, the potent caspase 3 inhibitor Z-VAD-FMK attenuated the morphological changes elicited by wasp venom and afforded protection to BTI-TN-5B1-4 cells.

Insights into the venom composition of the ectoparasitoid wasp Nasonia vitripennis from bioinformatic and proteomic studies

With the Nasonia vitripennis genome sequences available, we attempted to determine the proteins present in venom by two different approaches. First, we searched for the transcripts of venom proteins by a bioinformatic approach using amino acid sequences of known hymenopteran venom proteins. Second, we performed proteomic analyses of crude N. vitripennis venom removed from the venom reservoir, implementing both an off-line two-dimensional liquid chromatography matrix-assisted laser desorption/ ionization time-of-flight (2D-LC-MALDI-TOF) mass spectrometry (MS) and a two-dimensional liquid chromatography electrospray ionization Founer transform ion cyclotron resonance (2D-LC-ESI-FT-ICR) MS setup. This combination of bioinformatic and proteomic studies resulted in an extraordinary richness of identified venom constituents. Moreover, half of the 79 identified proteins were not yet associated with insect venoms: 16 proteins showed similarity only to known proteins from other tissues or secretions, and an additional 23 did not show similarity to any known protein. Serine proteases and their inhibitors were the most represented. Fifteen nonsecretory proteins were also identified by proteomic means and probably represent so-called 'venom trace elements'. The present study contributes greatly to the understanding of the biological diversity of the venom of parasitoid wasps at the molecular level.

Age and diet influence the composition of venom from the endoparasitic wasp Pimpla turionellae L. (Hymenoptera: Ichneumonidae)

Venom from the endoparasitic wasp Pimpla turionellae L. (Hymenoptera: Ichneumonidae) was found to contain a complex mixture of biogenic amines, noradrenalin, phospholipase B, and several proteins and peptides. The amount of noradrenalin and serotonin was found to be highest in venom from newly emerged wasps and decreased with age. Histamine was detected in minute amounts in comparison to the other venom components, and declined with increasing age of the parasitoids. Total peptides and proteins detected by reversed-phase HPLC increased with host age. Old-aged (30-33 days after emergence) wasps contained 2-fold more phospholipase B than young (<10 days [d] old) or medium-aged (10-22-d-old) females. Increases in phospholipase B alone, however, did not account for all changes in total venom protein because by 40 days after emergence, the levels of this enzyme began to decline while the amount of total protein was higher than in younger wasps. For all venom components detected, the amount present in the venom sharply decreased following host exposure. This was presumed to be the result of venom depletion associated with envenomation. Consistent with this view were the modest increases in venom components in wasps displaying a decreased rate of parasitization. When adult females were offered honey alone or in combination with feeding on hosts, no significant changes in venom composition were observed, with the exception of noradrenalin, which was found to be 5 times higher in concentration in wasps fed honey only. These results suggest that wasp age and incidence of parasitism are more important features influencing the composition of venom than the diet of adult females.

Characterization of phenoloxidase activity in venom from the ectoparasitoid Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae)

Crude venom isolated from the ectoparasitic wasp Nasonia vitripennis was found to possess phenoloxidase (PO) activity. Enzyme activity was detected by using a modified dot blot analysis approach in which venom samples were applied to nylon membranes and incubated with either L-DOPA or dopamine. Dot formation was most intense with dopamine as the substrate and no activators appeared to be necessary to evoke a melanization reaction. No melanization occurred when venom was incubated in Schneider's insect medium containing 10% fetal bovine serum or when using tyrosine as a substrate, but melanization did occur when larval or pupal plasma from the fly host, Sarcophaga bullata, was exposed to tyrosine. Only fly larval plasma induced an enzyme reaction with the Schneider's insect medium. The PO inhibitor phenylthiourea (PTU) and serine protease inhibitor phenylmethylsulfonylfluoride (PMSF) abolished PO activity in venom and host plasma samples, but glutathione (reduced) only inhibited venom PO. Elicitors of PO activity (sodium dodecyl sulfate and trypsin) had no or a modest effect (increase) on the ability of venom, or larval and pupal plasma to trigger melanization reactions. SDS-PAGE separation of crude venom followed by in-gel staining using L-DOPA as a substrate revealed two venom proteins with PO activity with estimated molecular weights of 68 and 160 kDa. In vitro assays using BTI-TN-5B1-4 cells were performed to determine the importance of venom PO in triggering cellular changes and evoking cell death. When cell monolayers were pre-treated with 10 mM PTU or PMSF prior to venom exposure, the cells were protected from the effects of venom intoxication as evidenced by no observable cellular morphological changes and over 90% cell viability by 24 h after venom treatment. Simultaneous addition of inhibitors with venom or lower concentrations of PMSF were less effective in affording protection. These observations collectively argue that wasp venom PO is unique from that of the fly hosts, and that the venom enzyme is critical in the intoxication pathway leading to cell death.