Production, composition, and mode of action of the painful defensive venom produced by a limacodid caterpillar, Doratifera vulnerans

The genome of the ant Tetramorium bicarinatum reveals a tandem organization of venom peptides genes allowing the prediction of their regulatory and evolutionary profiles

BACKGROUND

Venoms have evolved independently over a hundred times in the animal kingdom to deter predators and/or subdue prey. Venoms are cocktails of various secreted toxins, whose origin and diversification provide an appealing system for evolutionary researchers. Previous studies of the ant venom of Tetramorium bicarinatum revealed several Myrmicitoxin (MYRTX) peptides that gathered into seven precursor families suggesting different evolutionary origins. Analysis of the T. bicarinatum genome enabling further genomic approaches was necessary to understand the processes underlying the evolution of these myrmicitoxins.

RESULTS

Here, we sequenced the genome of Tetramorium bicarinatum and reported the organisation of 44 venom peptide genes (vpg). Of the eleven chromosomes that make up the genome of T. bicarinatum, four carry the vpg which are organized in tandem repeats. This organisation together with the ML evolutionary analysis of vpg sequences, is consistent with evolution by local duplication of ancestral genes for each precursor family. The structure of the vpg into two or three exons is conserved after duplication events while the promoter regions are the least conserved parts of the vpg even for genes with highly identical sequences. This suggests that enhancer sequences were not involved in duplication events, but were recruited from surrounding regions. Expression level analysis revealed that most vpg are highly expressed in venom glands, although one gene or group of genes is much more highly expressed in each family. Finally, the examination of the genomic data revealed that several genes encoding transcription factors (TFs) are highly expressed in the venom glands. The search for binding sites (BS) of these TFs in the vpg promoters revealed hot spots of GATA sites in several vpg families.

CONCLUSION

In this pioneering investigation on ant venom genes, we provide a high-quality assembly genome and the annotation of venom peptide genes that we think can fosters further genomic research to understand the evolutionary history of ant venom biochemistry.

Proteome of urticating setae of Ochrogaster lunifer, a processionary caterpillar of medical and veterinary importance, including primary structures of putative toxins

Ochrogaster lunifer (Lepidoptera: Notodontidae) is an Australian processionary caterpillar with detachable urticating setae that have a defensive function. These true setae induce inflammation when they contact human skin, and equine foetal loss syndrome if they are accidentally ingested by gravid horses. We used transcriptomics and proteomics to identify proteins and peptides present in and on urticating setae, which may include toxins that contribute to inflammation and/or foetal loss syndromes. This process identified 37 putative toxins, including multiple homologues of the honeybee venom peptide secapin, and proteins with similarity to odorant binding proteins, arylphorins, and the insect immune modulator Diedel. This work identifies candidate molecules that may contribute to the adverse effects of processionary caterpillar setae on human and animal health.

Horizontal gene transfer underlies the painful stings of asp caterpillars (Lepidoptera: Megalopygidae)

Larvae of the genus Megalopyge (Lepidoptera: Zygaenoidea: Megalopygidae), known as asp or puss caterpillars, produce defensive venoms that cause severe pain. Here, we present the anatomy, chemistry, and mode of action of the venom systems of caterpillars of two megalopygid species, the Southern flannel moth Megalopyge opercularis and the black-waved flannel moth Megalopyge crispata. We show that megalopygid venom is produced in secretory cells that lie beneath the cuticle and are connected to the venom spines by canals. Megalopygid venoms consist of large aerolysin-like pore-forming toxins, which we have named megalysins, and a small number of peptides. The venom system differs markedly from those of previously studied venomous zygaenoids of the family Limacodidae, suggestive of an independent origin. Megalopygid venom potently activates mammalian sensory neurons via membrane permeabilization and induces sustained spontaneous pain behavior and paw swelling in mice. These bioactivities are ablated by treatment with heat, organic solvents, or proteases, indicating that they are mediated by larger proteins such as the megalysins. We show that the megalysins were recruited as venom toxins in the Megalopygidae following horizontal transfer of genes from bacteria to the ancestors of ditrysian Lepidoptera. Megalopygids have recruited aerolysin-like proteins as venom toxins convergently with centipedes, cnidarians, and fish. This study highlights the role of horizontal gene transfer in venom evolution.

Venom composition and bioactive RF-amide peptide toxins of the saddleback caterpillar, Acharia stimulea (Lepidoptera: Limacodidae)

Limacodidae is a family of lepidopteran insects comprising >1500 species. More than half of these species produce pain-inducing defensive venoms in the larval stage, but little is known about their venom toxins. Recently, we characterised proteinaceous toxins from the Australian limacodid caterpillar Doratifera vulnerans, but it is unknown if the venom of this species is typical of other Limacodidae. Here, we use single animal transcriptomics and venom proteomics to investigate the venom of an iconic limacodid, the North American saddleback caterpillar Acharia stimulea. We identified 65 venom polypeptides, grouped into 31 different families. Neurohormones, knottins, and homologues of the immune signaller Diedel make up the majority of A.stimulea venom, indicating strong similarities to D. vulnerans venom, despite the large geographic separation of these caterpillars. One notable difference is the presence of RF-amide peptide toxins in A. stimulea venom. Synthetic versions of one of these RF-amide toxins potently activated the human neuropeptide FF1 receptor, displayed insecticidal activity when injected into Drosophila melanogaster, and moderately inhibited larval development of the parasitic nematode Haemonchus contortus. This study provides insights into the evolution and activity of venom toxins in Limacodidae, and provides a platform for future structure-function characterisation of A.stimulea peptide toxins.

Characterization of the natural peptidome of four leeches by integrated proteogenomics and pseudotargeted peptidomics

Animal-derived drugs are an indispensable part of folk medicine worldwide. However, their chemical constituents are poorly approached, which leads to the low level of the quality standard system of animal-derived drugs and further causes a chaotic market. Natural peptides are ubiquitous throughout the organism, especially in animal-derived drugs. Thus, in this study, we used multi-source leeches, including Hirudo nipponica (HN), Whitmania pigra (WP), Whitmania acranulata (WA), and Poecilobdella manillensis (PM), as a model. A strategy integrating proteogenomics and novel pseudotargeted peptidomics was developed to characterize the natural peptide phenotype and screen for signature peptides of four leech species. First, natural peptides were sequenced against an in-house annotated protein database of closely related species constructed from RNA-seq data from the Sequence Read Archive (SRA) website, which is an open-sourced public archive resource. Second, a novel pseudotargeted peptidomics integrating peptide ion pair extraction and retention time transfer was established to achieve high coverage and quantitative accuracy of the natural peptides and to screen for signature peptides for species authentication. In all, 2323 natural peptides were identified from four leech species whose databases were poorly annotated. The strategy was shown to significantly improve peptide identification. In addition, 36 of 167 differential peptides screened by pseudotargeted proteomics were identified, and about one-third of them came from the leucine-rich repeat domain (LRR) proteins, which are widely distributed in organisms. Furthermore, six signature peptides were screened with good specificity and stability, and four of them were validated by synthetic standards. Finally, a dynamic multiple reaction monitoring (dMRM) method based on these signature peptides was established and revealed that one-half of the commercial samples and all of the Tongxinluo capsules were derived from WP. All in all, the strategy developed in this study was effective for natural peptide characterization and signature peptide screening, which could also be applied to other animal-derived drugs, especially for modelless species that are less studied in protein database annotation.

An Assassin's Secret: Multifunctional Cytotoxic Compounds in the Predation Venom of the Assassin Bug Psytalla horrida (Reduviidae, Hemiptera)

Predatory assassin bugs produce venomous saliva that enables them to overwhelm, kill, and pre-digest large prey animals. Venom from the posterior main gland (PMG) of the African assassin bug Psytalla horrida has strong cytotoxic effects, but the responsible compounds are yet unknown. Using cation-exchange chromatography, we fractionated PMG extracts from P. horrida and screened the fractions for toxicity. Two venom fractions strongly affected insect cell viability, bacterial growth, erythrocyte integrity, and intracellular calcium levels in Drosophila melanogaster olfactory sensory neurons. LC-MS/MS analysis revealed that both fractions contained gelsolin, redulysins, S1 family peptidases, and proteins from the uncharacterized venom protein family 2. Synthetic peptides representing the putative lytic domain of redulysins had strong antimicrobial activity against Escherichia coli and/or Bacillus subtilis but only weak toxicity towards insect or mammalian cells, indicating a primary role in preventing the intake of microbial pathogens. In contrast, a recombinant venom protein family 2 protein significantly reduced insect cell viability but exhibited no antibacterial or hemolytic activity, suggesting that it plays a role in prey overwhelming and killing. The results of our study show that P. horrida secretes multiple cytotoxic compounds targeting different organisms to facilitate predation and antimicrobial defense.

Exploring the antibacterial potential of venoms from Argentinian animals

The resistance to antimicrobials developed by several bacterial species has become one of the main health problems in recent decades. It has been widely reported that natural products are important sources of antimicrobial compounds. Considering that animal venoms are under-explored in this line of research, in this study, we screened the antibacterial activity of venoms of eight snake and five lepidopteran species from northeastern Argentina. Twofold serial dilutions of venoms were tested by the agar well-diffusion method and the minimum inhibitory concentration (MIC) determination against seven bacterial strains. We studied the comparative protein profile of the venoms showing antibacterial activity. Only the viperid and elapid venoms showed remarkable dose-dependent antibacterial activity towards most of the strains tested. Bothrops diporus venom showed the lowest MIC values against all the strains, and S. aureus ATCC 25923 was the most sensitive strain for all the active venoms. Micrurus baliocoryphus venom was unable to inhibit the growth of Enterococcus faecalis. Neither colubrid snake nor lepidopteran venoms exhibited activity on any bacterial strain tested. The snake venoms exhibiting antibacterial activity showed distinctive protein profiles by SDS-PAGE, highlighting that we could reveal for the first time the main protein families which may be thought to contribute to the antibacterial activity of M. baliocoryphus venom. This study paves the way to search for new antibacterial agents from Argentinian snake venoms, which may be a further opportunity to give an added value to the local biodiversity.

Venom biotechnology: casting light on nature's deadliest weapons using synthetic biology

Venoms are complex chemical arsenals that have evolved independently many times in the animal kingdom. Venoms have attracted the interest of researchers because they are an important innovation that has contributed greatly to the evolutionary success of many animals, and their medical relevance offers significant potential for drug discovery. During the last decade, venom research has been revolutionized by the application of systems biology, giving rise to a novel field known as venomics. More recently, biotechnology has also made an increasing impact in this field. Its methods provide the means to disentangle and study venom systems across all levels of biological organization and, given their tremendous impact on the life sciences, these pivotal tools greatly facilitate the coherent understanding of venom system organization, development, biochemistry, and therapeutic activity. Even so, we lack a comprehensive overview of major advances achieved by applying biotechnology to venom systems. This review therefore considers the methods, insights, and potential future developments of biotechnological applications in the field of venom research. We follow the levels of biological organization and structure, starting with the methods used to study the genomic blueprint and genetic machinery of venoms, followed gene products and their functional phenotypes. We argue that biotechnology can answer some of the most urgent questions in venom research, particularly when multiple approaches are combined together, and with other venomics technologies.

Unraveling the venom chemistry with evidence for histamine as key regulator in the envenomation by caterpillar Automeris zaruma

Over the past decades, envenomation by caterpillars of Automeris spp. became an increasing health problem in Latin America. Accidental contact with the stinging spines of these caterpillars cause acute local pain, itching, inflammation and skin rashes that persists for days. Even when the cause is obvious, the exact molecular mechanisms responsible for the observed symptoms are yet to be elucidated. Here, we describe for the first time, an active compound in the venom and the study of the bioactivity of the venom extracted from the spines of the caterpillar Automeris zaruma. Electrophysiological screening of a library of membrane proteins important for pain and itch enabled us to investigate and reveal the mode of action of the venom of A. zaruma. Further mass spectrometric analysis (Q-TOF-MS) made it possible to establish a link between the bioactivity and the components found in the venom. We show that the spine extract of A. zaruma contains histamine that potently activates the four types of the human histamine receptors (H1R, H2R, H3R and H4R) with a selectivity preference towards H3R and H4R. Furthermore, a modulation of the target MRGPRX2 was found. Together, these findings are the first to explain the symptomology of A. zaruma envenomation, enabling us a better understanding of caterpillar envenomation and predict that the hurdle of the scarce efficacy of the currently used antihistaminic drugs can be overcome by including H3R and H4R blockers in the clinical used medication. Such an approach might be used for other caterpillar envenomation in the world and represent a significant improvement for the well-being of the patient.

Venomics of the Central European Myrmicine Ants Myrmica rubra and Myrmica ruginodis

Animal venoms are a rich source of novel biomolecules with potential applications in medicine and agriculture. Ants are one of the most species-rich lineages of venomous animals. However, only a fraction of their biodiversity has been studied so far. Here, we investigated the venom components of two myrmicine (subfamily Myrmicinae) ants: Myrmica rubra and Myrmica ruginodis. We applied a venomics workflow based on proteotranscriptomics and found that the venoms of both species are composed of several protein classes, including venom serine proteases, cysteine-rich secretory protein, antigen 5 and pathogenesis-related 1 (CAP) superfamily proteins, Kunitz-type serine protease inhibitors and venom acid phosphatases. Several of these protein classes are known venom allergens, and for the first time we detected phospholipase A1 in the venom of M. ruginodis. We also identified two novel epidermal growth factor (EGF) family toxins in the M. ruginodis venom proteome and an array of additional EGF-like toxins in the venom gland transcriptomes of both species. These are similar to known toxins from the related myrmicine ant, Manica rubida, and the myrmecine (subfamily Myrmeciinae) Australian red bulldog ant Myrmecia gullosa, and are possibly deployed as weapons in defensive scenarios or to subdue prey. Our work suggests that M.rubra and M. ruginodis venoms contain many enzymes and other high-molecular-weight proteins that cause cell damage. Nevertheless, the presence of EGF-like toxins suggests that myrmicine ants have also recruited smaller peptide components into their venom arsenal. Although little is known about the bioactivity and function of EGF-like toxins, their presence in myrmicine and myrmecine ants suggests they play a key role in the venom systems of the superfamily Formicoidea. Our work adds to the emerging picture of ant venoms as a source of novel bioactive molecules and highlights the need to incorporate such taxa in future venom bioprospecting programs.

Evolution, expression patterns and distribution of novel ribbon worm predatory and defensive toxins

Ribbon worms are active predators that use an eversible proboscis to inject venom into their prey and defend themselves with toxic epidermal secretions. Previous work on nemertean venom has largely focused on just a few species and has not investigated the different predatory and defensive secretions in detail. Consequently, our understanding of the composition and evolution of ribbon worm venoms is still very limited. Here, we present a comparative study of nemertean venom combining RNA-seq differential gene expression analyses of venom-producing tissues, tandem mass spectrometry-based proteomics of toxic secretions, and mass spectrometry imaging of proboscis sections, to shed light onto the composition and evolution of predatory and defensive toxic secretions in Antarctonemertes valida. Our analyses reveal a wide diversity of putative defensive and predatory toxins with tissue-specific gene expression patterns and restricted distributions to the mucus and proboscis proteomes respectively, suggesting that ribbon worms produce distinct toxin cocktails for predation and defense. Our results also highlight the presence of numerous lineage-specific toxins, indicating that venom evolution is highly divergent across nemerteans, producing toxin cocktails that might be finely tuned to subdue different prey. Our data also suggest that the hoplonemertean proboscis is a highly specialized predatory organ that seems to be involved in a variety of biological functions besides predation, including secretion and sensory perception. Overall, our results advance our knowledge into the diversity and evolution of nemertean venoms and highlight the importance of combining different types of data to characterize toxin composition in understudied venomous organisms.

Find My Way to You: A Comparative Study of Antennal Sensilla and Olfactory Genes in Slug Moth With Different Diet Ranges (Lepidoptera: Limacodidae)

Insects and plants that provide them with foods have coexisted for several hundred million years, which leads to various defense approaches and insect-feeding strategies. The host plant provides insects with food sources, shelter materials, and oviposition sites for phytophagous insects. However, they need to find the most suitable host plants in complicated plant communities. The antenna is the main sensory organ of insects, housing different types of sensilla dedicated to detecting chemical cues, motion, humidity, and temperature. Phytophagous insects with different diets may possess various adaptations in their olfactory system. We selected three species of slug moth (Narosoideus flavidorsalis, Chalcoscelides castaneipars, and Setora postornata) with different diet breadths to detect the structural diversity of antennal sensilla using the scanning electron microscope. A total of nine types of sensilla were identified in these three species, in which two types of sensilla (sensilla uniporous peg and sensilla furcatea) were the first found and reported in Limacodidae. By comparing the number of sensilla types, there was a trend of gradually decreasing the number of sensory types with the gradual expansion of feeding habitats. To better understand the vital roles of olfactory proteins in localizing host plants, we investigated the chemosensory proteins in the antennal transcriptomes of N. flavidorsalis and S. postornata. However, there was no significant correlation between the number of olfactory genes and the increase of antennal sensilla types. Combining antennal morphology, transcriptome analysis, and the prediction of suitable areas, we better understood the olfactory systems with different feeding preferences, which will provide new prospects for plant–insect interactions and population control methods.

Multipurpose peptides: The venoms of Amazonian stinging ants contain anthelmintic ponericins with diverse predatory and defensive activities

In the face of increasing drug resistance, the development of new anthelmintics is critical for controlling nematodes that parasitise livestock. Although hymenopteran venom toxins have attracted attention for applications in agriculture and medicine, few studies have explored their potential as anthelmintics. Here we assessed hymenopteran venoms as a possible source of new anthelmintic compounds by screening a panel of ten hymenopteran venoms against Haemonchus contortus, a major pathogenic nematode of ruminants. Using bioassay-guided fractionation coupled with liquid chromatography-tandem mass spectrometry, we identified four novel anthelmintic peptides (ponericins) from the venom of the neotropical ant Neoponera commutata and the previously described ponericin M-PONTX-Na1b from Neoponera apicalis venom. These peptides inhibit H. contortus development with IC₅₀ values of 2.8-5.6 μM. Circular dichroism spectropolarimetry indicated that the ponericins are unstructured in aqueous solution but adopt α-helical conformations in lipid mimetic environments. We show that the ponericins induce non-specific membrane perturbation, which confers broad-spectrum antimicrobial, insecticidal, cytotoxic, hemolytic, and algogenic activities, with activity across all assays typically correlated. We also show for the first time that ponericins induce spontaneous pain behaviour when injected in mice. We propose that the broad-spectrum activity of the ponericins enables them to play both a predatory and defensive role in neoponeran ants, consistent with their high abundance in venom. This study reveals a broader functionality for ponericins than previously assumed, and highlights both the opportunities and challenges in pursuing ant venom peptides as potential therapeutics.