Novel venom proteins produced by differential domain-expression strategies in beaded lizards and gila monsters (genus Heloderma)

Mandibular gland proteomics of the Mexican alligator lizard, Abronia graminea, and the red-lipped arboreal alligator lizard, Abronia lythrochila

A useful approach to deepen our knowledge about the origin and evolution of venom systems in Reptilia has been exploring the vast biodiversity of this clade of vertebrates in search of orally produced proteins with toxic actions, as well as their corresponding delivery systems. The occurrence of toxins in anguimorph lizards has been demonstrated experimentally or inferred from reports of the toxic effects of the oral secretions of taxa within the Varanidae and Helodermatidae families. In the present study, we have focused on two alligator lizards of the Anguidae family, the Mexican alligator lizard, Abronia graminea, and the red-lipped arboreal alligator lizard, A. lythrochila. In addition, the fine morphology of teeth of the latter species is described. The presence of a conserved set of proteins, including B-type natriuretic peptides, cysteine-rich secretory proteins, group III phospholipase A2, and kallikrein, in submandibular gland extracts was demonstrated for both Abronia species. These proteins belong to toxin families found in oral gland secretions of venomous reptile species. This finding, along with previous demonstration of toxin-producing taxa in both paleo- and neoanguimorpha clades, provides further support for the existence of a handful of conserved toxin families in oral secretions across the 100+ million years of Anguimorpha cladogenesis.

Proteomic Analysis of Heloderma horridum horridum Venom: Assessment to Its Transcriptome and Newfound Proteins

Heloderma horridum horridum, a venomous reptile native to America, has a venom with potential applications in treating type II diabetes. In this work, H. h. horridum venom was extracted, lyophilized, and characterized using enzymatic assays for hyaluronidase, phospholipase, and protease. Proteomic analysis of the venom was conducted employing bottom-up/shotgun approaches, SDS-PAGE, high-pH reversed-phase chromatography, and fractionation of tryptic peptides using nano-LC-MS/MS. The proteins found in H. h. horridum venom were reviewed according to the classification of the transcriptome previously reported. The proteomic approach identified 101 enzymes, 36 other proteins, 15 protein inhibitors, 11 host defense proteins, and 1 toxin, including novel venom components such as calcium-binding proteins, phospholipase A2 inhibitors, serpins, cathepsin, subtilases, carboxypeptidase-like, aminopeptidases, glycoside hydrolases, thioredoxin transferases, acid ceramidase-like, enolase, multicopper oxidases, phosphoglucose isomerase (PGI), fructose-1,6-bisphosphatase class 1, pentraxin-related, peptidylglycine α-hydroxylating monooxygenase/peptidyl-hydroxyglycine α-amidating lyase, carbonic anhydrase, acetylcholinesterase, dipeptidylpeptidase, and lysozymes. These findings contribute to understanding the venomous nature of H. h. horridum and highlight its potential as a source of bioactive compounds. Data are available via PRoteomeXchange with the identifier PXD052417.

The Clot Thickens: Differential Coagulotoxic and Cardiotoxic Activities of Anguimorpha Lizard Venoms

Despite their evolutionary novelty, lizard venoms are much less studied in comparison to the intense research on snake venoms. While the venoms of helodermatid lizards have long been assumed to be for defensive purposes, there is increasing evidence of toxic activities more useful for predation than defence (such as paralytic neurotoxicity). This study aimed to ascertain the effects of Heloderma, Lanthanotus, and Varanus lizard venoms on the coagulation and cardiovascular systems. Anticoagulant toxicity was demonstrated for the Varanus species studied, with the venoms prolonging clotting times in human and bird plasma due to the destructive cleavage of fibrinogen. In contrast, thromboelastographic analyses on human and bird plasmas in this study demonstrated a procoagulant bioactivity for Heloderma venoms. A previous study on Heloderma venom using factor-depleted plasmas as a proxy model suggested a procoagulant factor was present that activated either Factor XI or Factor XII, but could not ascertain the precise target. Our activation studies using purified zymogens confirmed FXII activation. Comparisons of neonate and adult H. exasperatum, revealed the neonates to be more potent in the ability to activate FXII, being more similar to the venom of the smaller species H. suspectum than the adult H. exasperatum. This suggests potent FXII activation a basal trait in the genus, present in the small bodied last common ancestor. This also indicates an ontogenetic difference in prey preferences in the larger Heloderma species paralleing the change in venom biochemistry. In addition, as birds lack Factor XII, the ability to clot avian plasma suggested an additional procoagulant site of action, which was revealed to be the activation of Factor VII, with H. horridum being the most potent. This study also examined the effects upon the cardiovascular system, including the liberation of kinins from kininogen, which contributes to hypotension induction. This form of toxicity was previously described for Heloderma venoms, and was revealed in this study was to also be a pathophysiological effect of Lanthanotus and Varanus venoms. This suggests that this toxic activity was present in the venom of the last common ancestor of the anguimorph lizards, which is consistent with kallikrein enzymes being a shared toxin trait. This study therefore uncovered novel actions of anguimorph lizard venoms, not only contributing to the evolutionary biology body of knowledge but also revealing novel activities to mine for drug design lead compounds.

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.

Proteomic analysis of the mandibular glands from the Chinese crocodile lizard, Shinisaurus crocodilurus - Another venomous lizard?

Based on its phylogenetic relationship to monitor lizards (Varanidae), Gila monsters (Heloderma spp.), and the earless monitor Lanthanotus borneesis, the Chinese crocodile lizard, Shinisaurus crocodilurus, has been assigned to the Toxicofera clade, which comprises venomous reptiles. However, no data about composition and biological activities of its oral secretion have been reported. In the present study, a proteomic analysis of the mandibular gland of S. crocodilurus and, for comparison, of the herbivorous Solomon Island skink Corucia zebrata, was performed. Scanning electron microscopy (SEM) of the teeth from S. crocodilurus revealed a sharp ridge on the anterior surface, but no grooves, whereas those of C. zebrata possess a flattened crown with a pointed cusp. Proteomic analysis of their gland extracts provided no evidence of venom-derived peptides or proteins, strongly supporting the non-venomous character of these lizards. Data are available via ProteomeXchange with identifier PXD039424.

The Two Domains of the Avian Double-β-Defensin AvBD11 Have Different Ancestors, Common with Potential Monodomain Crocodile and Turtle Defensins

Simple Summary

Vertebrate defensins are a multigene family of antimicrobial peptides that evolved following a series of gene duplication and divergence events during the expansion of vertebrates. In birds, the repertoire of avian defensins contains an atypical defensin, namely AvBD11 (avian beta-defensin 11), which consists of two repeated but divergent defensin units (or domains) while most vertebrate defensins only possess one unit. In this study, we investigated the evolutionary scenario leading to the formation of this double defensin in birds by comparing each defensin unit of AvBD11 with other defensins from birds and closely related reptiles (crocodile, turtles) predicted to have a single defensin unit. Our most outstanding results suggest that the double defensin AvBD11 probably appeared following a fusion of two ancestral genes or from an ancestral double defensin, but not from a recent internal duplication as it can be observed in other types of proteins with domain repeats.

Abstract

Beta-defensins are an essential group of cysteine-rich host-defence peptides involved in vertebrate innate immunity and are generally monodomain. Among bird defensins, the avian β-defensin 11 (AvBD11) is unique because of its peculiar structure composed of two β-defensin domains. The reasons for the appearance of such ‘polydefensins’ during the evolution of several, but not all branches of vertebrates, still remain an open question. In this study, we aimed at exploring the origin and evolution of the bird AvBD11 using a phylogenetic approach. Although they are homologous, the N- and C-terminal domains of AvBD11 share low protein sequence similarity and possess different cysteine spacing patterns. Interestingly, strong variations in charge properties can be observed on the C-terminal domain depending on bird species but, despite this feature, no positive selection was detected on the AvBD11 gene (neither on site nor on branches). The comparison of AvBD11 protein sequences in different bird species, however, suggests that some amino acid residues may have undergone convergent evolution. The phylogenetic tree of avian defensins revealed that each domain of AvBD11 is distant from ovodefensins (OvoDs) and may have arisen from different ancestral defensins. Strikingly, our phylogenetic analysis demonstrated that each domain of AvBD11 has common ancestors with different putative monodomain β-defensins from crocodiles and turtles and are even more closely related with these reptilian defensins than with their avian paralogs. Our findings support that AvBD11′s domains, which differ in their cysteine spacing and charge distribution, do not result from a recent internal duplication but most likely originate from a fusion of two different ancestral genes or from an ancestral double-defensin arisen before the Testudines-Archosauria split.

Neglected Venomous Animals and Toxins: Underrated Biotechnological Tools in Drug Development

Among the vast repertoire of animal toxins and venoms selected by nature and evolution, mankind opted to devote its scientific attention—during the last century—to a restricted group of animals, leaving a myriad of toxic creatures aside. There are several underlying and justifiable reasons for this, which include dealing with the public health problems caused by envenoming by such animals. However, these studies became saturated and gave rise to a whole group of animals that become neglected regarding their venoms and secretions. This repertoire of unexplored toxins and venoms bears biotechnological potential, including the development of new technologies, therapeutic agents and diagnostic tools and must, therefore, be assessed. In this review, we will approach such topics through an interconnected historical and scientific perspective that will bring up the major discoveries and innovations in toxinology, achieved by researchers from the Butantan Institute and others, and describe some of the major research outcomes from the study of these neglected animals.

Recent advances in the discovery of novel marine natural products and mycosporine-like amino acid UV-absorbing compounds

Abstract

Bioactive compounds from marine environments represent a rich source of bioproducts for potential use in medicine and biotechnology. To discover and identify novel marine natural products (MNPs), evaluating diverse biological activities is critical. Increased sensitivity and specificity of omics technologies, especially next-generation high-throughput sequencing combined with liquid chromatography-mass spectrometry and nuclear magnetic resonance, are speeding up the discovery of novel bioactive compounds. Mycosporine-like amino acids (MAAs) isolated from many marine microorganisms are among highly promising MNPs characterized by ultraviolet radiation (UV) absorbing capacities and are recognized as a potential source of ecologically friendly sunscreens. MAAs absorb damaging UV radiation with maximum absorption in the range of 310–360 nm, including both UVA and UVB ranges. MAAs are also characterized by other biological activities such as anti-oxidant, anti-cancer, and anti-inflammatory activities. The application of modern omics approaches promoted some recent developments in our understanding of MAAs’ functional significance and diversity. This review will summarize the various modern tools that could be applied during the identification and characterization of MNPs, including MAAs, to further their innovative applications.

Key points

• New omics technologies are speeding up the discovery of novel bio-products

• The vast diversity of bioactive capacities of marine natural products described

• Marine microorganisms as a source of environmentally friendly sunscreens

The Dragon's Paralysing Spell: Evidence of Sodium and Calcium Ion Channel Binding Neurotoxins in Helodermatid and Varanid Lizard Venoms

Bites from helodermatid lizards can cause pain, paresthesia, paralysis, and tachycardia, as well as other symptoms consistent with neurotoxicity. Furthermore, in vitro studies have shown that Heloderma horridum venom inhibits ion flux and blocks the electrical stimulation of skeletal muscles. Helodermatids have long been considered the only venomous lizards, but a large body of robust evidence has demonstrated venom to be a basal trait of Anguimorpha. This clade includes varanid lizards, whose bites have been reported to cause anticoagulation, pain, and occasionally paralysis and tachycardia. Despite the evolutionary novelty of these lizard venoms, their neuromuscular targets have yet to be identified, even for the iconic helodermatid lizards. Therefore, to fill this knowledge gap, the venoms of three Heloderma species (H. exasperatum, H. horridum and H. suspectum) and two Varanus species (V. salvadorii and V. varius) were investigated using Gallus gallus chick biventer cervicis nerve–muscle preparations and biolayer interferometry assays for binding to mammalian ion channels. Incubation with Heloderma venoms caused the reduction in nerve-mediated muscle twitches post initial response of avian skeletal muscle tissue preparation assays suggesting voltage-gated sodium (Na_V) channel binding. Congruent with the flaccid paralysis inducing blockage of electrical stimulation in the skeletal muscle preparations, the biolayer interferometry tests with Heloderma suspectum venom revealed binding to the S3–S4 loop within voltage-sensing domain IV of the skeletal muscle channel subtype, Na_V1.4. Consistent with tachycardia reported in clinical cases, the venom also bound to voltage-sensing domain IV of the cardiac smooth muscle calcium channel, Ca_V1.2. While Varanus varius venom did not have discernable effects in the avian tissue preparation assay at the concentration tested, in the biointerferometry assay both V. varius and V. salvadorii bound to voltage-sensing domain IV of both Na_V1.4 and Ca_V1.2, similar to H. suspectum venom. The ability of varanid venoms to bind to mammalian ion channels but not to the avian tissue preparation suggests prey-selective actions, as did the differential potency within the Heloderma venoms for avian versus mammalian pathophysiological targets. This study thus presents the detailed characterization of Heloderma venom ion channel neurotoxicity and offers the first evidence of varanid lizard venom neurotoxicity. In addition, the data not only provide information useful to understanding the clinical effects produced by envenomations, but also reveal their utility as physiological probes, and underscore the potential utility of neglected venomous lineages in the drug design and development pipeline.

The Origin and Evolution of Antistasin-like Proteins in Leeches (Hirudinida, Clitellata)

Bloodfeeding is employed by many parasitic animals and requires specific innovations for efficient feeding. Some of these innovations are molecular features that are related to the inhibition of hemostasis. For example, bloodfeeding insects, bats, and leeches release proteins with anticoagulatory activity through their salivary secretions. The antistasin-like protein family, composed of serine protease inhibitors with one or more antistasin-like domains, is tightly linked to inhibition of hemostasis in leeches. However, this protein family has been recorded also in non-bloodfeeding invertebrates, such as cnidarians, mollusks, polychaetes, and oligochaetes. The present study aims to 1) root the antistasin-like gene tree and delimit the major orthologous groups, 2) identify potential independent origins of salivary proteins secreted by leeches, and 3) identify major changes in domain and/or motif structure within each orthologous group. Five clades containing leech antistasin-like proteins are distinguishable through rigorous phylogenetic analyses based on nine new transcriptomes and a diverse set of comparative data: the trypsin + leukocyte elastase inhibitors clade, the antistasin clade, the therostasin clade, and two additional, unnamed clades. The antistasin-like gene tree supports multiple origins of leech antistasin-like proteins due to the presence of both leech and non-leech sequences in one of the unnamed clades, but a single origin of factor Xa and trypsin + leukocyte elastase inhibitors. This is further supported by three sequence motifs that are exclusive to antistasins, the trypsin + leukocyte elastase inhibitor clade, and the therostasin clade, respectively. We discuss the implications of our findings for the evolution of this diverse family of leech anticoagulants.

The earless monitor lizard Lanthanotus borneensis - A venomous animal?

Based on its mandibular gland secretion, the earless monitor lizard, Lanthanotus borneensis, has been considered a venomous animal like other members of the Toxicofera group, including Heloderma. In the present study, the gland structure and teeth of L. borneensis were examined by micro-tomography (μCT) and scanning electron microscopy (SEM), respectively, and proteomic analysis of the gland extract was performed. The mandibular gland consists of six compartments with separate ducts. The pleurodont teeth of the lower and upper jaw are not grooved but possess a sharp ridge on the anterior surface. Proteomic analysis of the gland extract confirmed previous studies that kallikrein enzymes are the major biologically active components. In view of the lizard's biology, its mandibular gland secretion is obviously not needed for prey capture or defence. It seems not justified the labelling of L. borneensis as a venomous animal. However, definitively answering this question requires toxinological studies on natural prey.

Identification, Purification and Molecular Characterization of Chondrosin, a New Protein with Anti-tumoral Activity from the Marine Sponge Chondrosia Reniformis Nardo 1847

: Chondrosia reniformis is a common marine demosponge showing many peculiarities, lacking silica spicules and with a body entirely formed by a dense collagenous matrix. In this paper, we have described the identification of a new cytotoxic protein (chondrosin) with selective activity against specific tumor cell lines, from C. reniformis, collected from the Liguria Sea. Chondrosin was extracted and purified using a salting out approach and molecular weight size exclusion chromatography. The cytotoxic fractions were then characterized by two-dimensional gel electrophoresis and mass spectrometry analysis and matched the results with C. reniformis transcriptome database. The procedure allowed for identifying a full-length cDNA encoding for a 199-amino acids (aa) polypeptide, with a signal peptide of 21 amino acids. The mature protein has a theoretical molecular weight of 19611.12 and an IP of 5.11. Cell toxicity assays showed a selective action against some tumor cell lines (RAW 264.7 murine leukemia cells in particular). Cell death was determined by extracellular calcium intake, followed by cytoplasmic reactive oxygen species overproduction. The in silico modelling of chondrosin showed a high structural homology with the N-terminal region of the ryanodine receptor/channel and a short identity with defensin. The results are discussed suggesting a possible specific interaction of chondrosin with the Cav 1.3 ion voltage calcium channel expressed on the target cell membranes.

Molecular evolution of GIP and Exendin and their receptors

Glucose-dependent insulinotropic polypeptide (GIP) is a product of the Gip gene and acts as an incretin hormone in mammals. Gip is most closely related to the proglucagon (Gcg) and Exendin genes and diverged from these very early in vertebrate evolution. In mammals, GIP acts through its specific receptor, encoded by the Gipr gene, which belongs to a subfamily of 7-transmembrane G-protein coupled receptor (GPCR) genes that also includes those for the proglucagon-derived peptides (Gcgr, Glp1r, and Glp2r), and the receptor for Exendin (Grlr). Gip, Gipr, Exendin, and Grlr genes are found in species from most vertebrate classes. While most species that have a Gip gene also have a Gipr gene, two classes of vertebrates, cartilaginous fish and birds, retain conserved Gip genes but lack Gipr genes. This raises the possibility the GIP signals through other receptors in some vertebrates. Exendin genes and the gene for its receptor, Grlr, are also found in diverse vertebrates, with the notable exception of mammals. Both GIP and Exendin likely have important roles in vertebrate physiology, but their roles are either dispensable or can be replaced by other hormones.

Structure, function, and evolution of Gga-AvBD11, the archetype of the structural avian-double-β-defensin family

Out of the 14 avian β-defensins identified in the Gallus gallus genome, only 3 are present in the chicken egg, including the egg-specific avian β-defensin 11 (Gga-AvBD11). Given its specific localization and its established antibacterial activity, Gga-AvBD11 appears to play a protective role in embryonic development. Gga-AvBD11 is an atypical double-sized defensin, predicted to possess 2 motifs related to β-defensins and 6 disulfide bridges. The 3-dimensional NMR structure of the purified Gga-AvBD11 is a compact fold composed of 2 packed β-defensin domains. This fold is the archetype of a structural family, dubbed herein as avian-double-β-defensins (Av-DBD). We speculate that AvBD11 emanated from a monodomain gene ancestor and that similar events might have occurred in arthropods, leading to another structural family of less compact DBDs. We show that Gga-AvBD11 displays antimicrobial activities against gram-positive and gram-negative bacterial pathogens, the avian protozoan Eimeria tenella, and avian influenza virus. Gga-AvBD11 also shows cytotoxic and antiinvasive activities, suggesting that it may not only be involved in innate protection of the chicken embryo, but also in the (re)modeling of embryonic tissues. Finally, the contribution of either of the 2 Gga-AvBD11 domains to these biological activities was assessed, using chemically synthesized peptides. Our results point to a critical importance of the cationic N-terminal domain in mediating antibacterial, antiparasitic, and antiinvasive activities, with the C-terminal domain potentiating the 2 latter activities. Strikingly, antiviral activity in infected chicken cells, accompanied by marked cytotoxicity, requires the full-length protein.

Varanid Lizard Venoms Disrupt the Clotting Ability of Human Fibrinogen through Destructive Cleavage

The functional activities of Anguimorpha lizard venoms have received less attention compared to serpent lineages. Bite victims of varanid lizards often report persistent bleeding exceeding that expected for the mechanical damage of the bite. Research to date has identified the blockage of platelet aggregation as one bleeding-inducing activity, and destructive cleavage of fibrinogen as another. However, the ability of the venoms to prevent clot formation has not been directly investigated. Using a thromboelastograph (TEG5000), clot strength was measured after incubating human fibrinogen with Heloderma and Varanus lizard venoms. Clot strengths were found to be highly variable, with the most potent effects produced by incubation with Varanus venoms from the Odatria and Euprepriosaurus clades. The most fibrinogenolytically active venoms belonged to arboreal species and therefore prey escape potential is likely a strong evolutionary selection pressure. The results are also consistent with reports of profusive bleeding from bites from other notably fibrinogenolytic species, such as V. giganteus. Our results provide evidence in favour of the predatory role of venom in varanid lizards, thus shedding light on the evolution of venom in reptiles and revealing potential new sources of bioactive molecules useful as lead compounds in drug design and development.

Alternative Transcription at Venom Genes and Its Role as a Complementary Mechanism for the Generation of Venom Complexity in the Common House Spider

The complex composition of venom, a proteinaceous secretion used by diverse animal groups for predation or defense, is typically viewed as being driven by gene duplication in conjunction with positive selection, leading to large families of diversified toxins with selective venom gland expression. Yet, the production of alternative transcripts at venom genes is often overlooked as another potentially important process that could contribute proteins to venom, and requires comprehensive datasets integrating genome and transcriptome sequences together with proteomic characterization of venom to be fully documented. In the common house spider, Parasteatoda tepidariorum, we used RNA sequencing of four tissue types in conjunction with the sequenced genome to provide a comprehensive transcriptome annotation. We also used mass spectrometry to identify a minimum of 99 distinct proteins in P tepidariorum venom, including at least 33 latrotoxins, pore-forming neurotoxins shared with the confamilial black widow. We found that venom proteins are much more likely to come from multiple transcript genes, whose transcripts produced distinct protein sequences. The presence of multiple distinct proteins in venom from transcripts at individual genes was confirmed for eight loci by mass spectrometry, and is possible at 21 others. Alternative transcripts from the same gene, whether encoding or not encoding a protein found in venom, showed a range of expression patterns, but were not necessarily restricted to the venom gland. However, approximately half of venom protein encoding transcripts were found among the 1,318 transcripts with strongly venom gland biased expression. Our findings revealed an important role for alternative transcription in generating venom protein complexity and expanded the traditional model of venom evolution.

Arthropod venoms: Biochemistry, ecology and evolution

Comprising of over a million described species of highly diverse invertebrates, Arthropoda is amongst the most successful animal lineages to have colonized aerial, terrestrial, and aquatic domains. Venom, one of the many fascinating traits to have evolved in various members of this phylum, has underpinned their adaptation to diverse habitats. Over millions of years of evolution, arthropods have evolved ingenious ways of delivering venom in their targets for self-defence and predation. The morphological diversity of venom delivery apparatus in arthropods is astounding, and includes extensively modified pedipalps, tail (telson), mouth parts (hypostome), fangs, appendages (maxillulae), proboscis, ovipositor (stinger), and hair (urticating bristles). Recent investigations have also unravelled an astonishing venom biocomplexity with molecular scaffolds being recruited from a multitude of protein families. Venoms are a remarkable bioresource for discovering lead compounds in targeted therapeutics. Several components with prospective applications in the development of advanced lifesaving drugs and environment friendly bio-insecticides have been discovered from arthropod venoms. Despite these fascinating features, the composition, bioactivity, and molecular evolution of venom in several arthropod lineages remains largely understudied. This review highlights the prevalence of venom, its mode of toxic action, and the evolutionary dynamics of venom in Arthropoda, the most speciose phylum in the animal kingdom.

Comparative transcriptome analyses of venom glands from three scorpionfishes

Scorpionfishes (Scorpaenidae) are a relatively common cause of human envenomation. They often enter coastal waters and their stings can be quite hazardous, provoking extreme pain and causing the victims to take days to recover. There are few genomic resources available for the scorpionfishes. In this study, we elucidated the transcriptomic profile of the venom glands from three different scorpionfish species, namely Scorpaenopsis cirrosa, S. neglecta and S. possi. This is the first report of scorpionfish transcriptomes. After functional and pathway annotation, we employed toxin annotation to identify many species-specific (18, 13 and 19 respectively) and overlapping putative toxins among the three species. Our study represents a significant improvement in the genetic information about the venoms from these three species. Moreover, this work also provides an archive for future studies on evolution of fish toxins and can be used for comparative studies of other fishes.

Definition of the R-superfamily of conotoxins: Structural convergence of helix-loop-helix peptidic scaffolds

The F14 conotoxins define a four-cysteine, three-loop conotoxin scaffold that produce tightly folded structures held together by two disulfide bonds with a CCCC arrangement (conotoxin framework 14). Here we describe the precursors of the F14 conotoxins from the venom of Conus anabathrum and Conus villepinii. Using transcriptomic and cDNA cloning analysis, the full-length of the precursors of flf14a and flf14b from the transcriptome of C. anabathrum revealed a unique signal sequence that defines the new conotoxin R-superfamily. Using the signal sequence as a primer, we cloned seven additional previously undescribed toxins of the R-superfamily from C. villepinii. The propeptide regions of the R-conotoxins are unusually long and with prevalent proline residues in repeating pentads which qualifies them as Pro-rich motifs (PRMs), which can be critical for protein-protein interactions or they can be cleaved to release short linear peptides that may be part of the envenomation mélange. Additionally, we determined the three-dimensional structure of vil14a by solution ¹H-NMR and found that the structure of this conotoxin displays a cysteine-stabilized α-helix-loop-helix (C_s α/α) fold. The structure is well-defined over the helical regions (backbone RMSD for residues 2-13 and 17-26 is 0.63 ± 0.14 Å), with conformational flexibility in the triple Gly region of the second loop as well as the N- and C- termini. Structurally, the F14 conotoxins overlap with the C_s α/α scorpion toxins and other peptidic natural products, and in spite of their different exogenomic origins, there is convergence into this scaffold from several classes of living organisms that express these peptides.

α-Helix or β-Turn? An Investigation into N-Terminally Constrained Analogues of Glucagon-like Peptide 1 (GLP-1) and Exendin-4

Peptide agonists acting on the glucagon-like peptide 1 receptor (GLP-1R) promote glucose-dependent insulin release and therefore represent important therapeutic agents for type 2 diabetes (T2D). Previous data indicated that an N-terminal type II β-turn motif might be an important feature for agonists acting on the GLP-1R. In contrast, recent publications reporting the structure of the full-length GLP-1R have shown the N-terminus of receptor-bound agonists in an α-helical conformation. To reconcile these conflicting results, we prepared N-terminally constrained analogues of glucagon-like peptide 1 (GLP-1) and exendin-4 and evaluated their receptor affinity and functionality in vitro; we then examined their crystal structures in complex with the extracellular domain of the GLP-1R and used molecular modeling and molecular dynamics simulations for further investigations. We report that the peptides' N-termini in all determined crystal structures adopted a type II β-turn conformation, but in vitro potency varied several thousand-fold across the series. Potency correlated better with α-helicity in our computational model, although we have found that the energy barrier between the two mentioned conformations is low in our most potent analogues and the flexibility of the N-terminus is highlighted by the dynamics simulations.

Proteomic Analyses of the Unexplored Sea Anemone Bunodactis verrucosa

Cnidarian toxic products, particularly peptide toxins, constitute a promising target for biomedicine research. Indeed, cnidarians are considered as the largest phylum of generally toxic animals. However, research on peptides and toxins of sea anemones is still limited. Moreover, most of the toxins from sea anemones have been discovered by classical purification approaches. Recently, high-throughput methodologies have been used for this purpose but in other Phyla. Hence, the present work was focused on the proteomic analyses of whole-body extract from the unexplored sea anemone Bunodactis verrucosa. The proteomic analyses applied were based on two methods: two-dimensional gel electrophoresis combined with MALDI-TOF/TOF and shotgun proteomic approach. In total, 413 proteins were identified, but only eight proteins were identified from gel-based analyses. Such proteins are mainly involved in basal metabolism and biosynthesis of antibiotics as the most relevant pathways. In addition, some putative toxins including metalloproteinases and neurotoxins were also identified. These findings reinforce the significance of the production of antimicrobial compounds and toxins by sea anemones, which play a significant role in defense and feeding. In general, the present study provides the first proteome map of the sea anemone B. verrucosa stablishing a reference for future studies in the discovery of new compounds.

Enter the Dragon: The Dynamic and Multifunctional Evolution of Anguimorpha Lizard Venoms

While snake venoms have been the subject of intense study, comparatively little work has been done on lizard venoms. In this study, we have examined the structural and functional diversification of anguimorph lizard venoms and associated toxins, and related these results to dentition and predatory ecology. Venom composition was shown to be highly variable across the 20 species of Heloderma, Lanthanotus, and Varanus included in our study. While kallikrein enzymes were ubiquitous, they were also a particularly multifunctional toxin type, with differential activities on enzyme substrates and also ability to degrade alpha or beta chains of fibrinogen that reflects structural variability. Examination of other toxin types also revealed similar variability in their presence and activity levels. The high level of venom chemistry variation in varanid lizards compared to that of helodermatid lizards suggests that venom may be subject to different selection pressures in these two families. These results not only contribute to our understanding of venom evolution but also reveal anguimorph lizard venoms to be rich sources of novel bioactive molecules with potential as drug design and development lead compounds.

From Marine Venoms to Drugs: Efficiently Supported by a Combination of Transcriptomics and Proteomics

The potential of marine natural products to become new drugs is vast; however, research is still in its infancy. The chemical and biological diversity of marine toxins is immeasurable and as such an extraordinary resource for the discovery of new drugs. With the rapid development of next-generation sequencing (NGS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), it has been much easier and faster to identify more toxins and predict their functions with bioinformatics pipelines, which pave the way for novel drug developments. Here we provide an overview of related bioinformatics pipelines that have been supported by a combination of transcriptomics and proteomics for identification and function prediction of novel marine toxins.

Convergent evolution of defensin sequence, structure and function

Defensins are a well-characterised group of small, disulphide-rich, cationic peptides that are produced by essentially all eukaryotes and are highly diverse in their sequences and structures. Most display broad range antimicrobial activity at low micromolar concentrations, whereas others have other diverse roles, including cell signalling (e.g. immune cell recruitment, self/non-self-recognition), ion channel perturbation, toxic functions, and enzyme inhibition. The defensins consist of two superfamilies, each derived from an independent evolutionary origin, which have subsequently undergone extensive divergent evolution in their sequence, structure and function. Referred to as the cis- and trans-defensin superfamilies, they are classified based on their secondary structure orientation, cysteine motifs and disulphide bond connectivities, tertiary structure similarities and precursor gene sequence. The utility of displaying loops on a stable, compact, disulphide-rich core has been exploited by evolution on multiple occasions. The defensin superfamilies represent a case where the ensuing convergent evolution of sequence, structure and function has been particularly extreme. Here, we discuss the extent, causes and significance of these convergent features, drawing examples from across the eukaryotes.

Monotreme glucagon-like peptide-1 in venom and gut: one gene - two very different functions

The importance of Glucagon like peptide 1 (GLP-1) for metabolic control and insulin release sparked the evolution of genes mimicking GLP-1 action in venomous species (e.g. Exendin-4 in Heloderma suspectum (gila monster)). We discovered that platypus and echidna express a single GLP-1 peptide in both intestine and venom. Specific changes in GLP-1 of monotreme mammals result in resistance to DPP-4 cleavage which is also observed in the GLP-1 like Exendin-4 expressed in Heloderma venom. Remarkably we discovered that monotremes evolved an alternative mechanism to degrade GLP-1. We also show that monotreme GLP-1 stimulates insulin release in cultured rodent islets, but surprisingly shows low receptor affinity and bias toward Erk signaling. We propose that these changes in monotreme GLP-1 are the result of conflicting function of this peptide in metabolic control and venom. This evolutionary path is fundamentally different from the generally accepted idea that conflicting functions in a single gene favour duplication and diversification, as is the case for Exendin-4 in gila monster. This provides novel insight into the remarkably different metabolic control mechanism and venom function in monotremes and an unique example of how different selective pressures act upon a single gene in the absence of gene duplication.

Viper Venom Botox: The Molecular Origin and Evolution of the Waglerin Peptides Used in Anti-Wrinkle Skin Cream

The molecular origin of waglerin peptides has remained enigmatic despite their industrial application in skin cream products to paralyse facial muscles and thus reduce the incidence of wrinkles. Here we show that these neurotoxic peptides are the result of de novo evolution within the prepro region of the C-type natriuretic peptide gene in Tropidolaemus venoms, at a site distinct from the domain encoding for the natriuretic peptide. It is the same region that yielded the azemiopsin peptides from Azemiops feae, indicative of a close relationship of this toxin gene between these two genera. The precursor region for the molecular evolution is a biodiversity hotspot that has yielded other novel bioactive peptides with novel activities. We detail the diversity of components in this and other species in order to explore what characteristics enable it to be such a biodiscovery treasure trove. The unusual function of Tropidolaemus venoms may have been selected for due to evolutionary pressures brought about by a high likelihood of prey escape.

The Snake with the Scorpion's Sting: Novel Three-Finger Toxin Sodium Channel Activators from the Venom of the Long-Glanded Blue Coral Snake (Calliophis bivirgatus)

Millions of years of evolution have fine-tuned the ability of venom peptides to rapidly incapacitate both prey and potential predators. Toxicofera reptiles are characterized by serous-secreting mandibular or maxillary glands with heightened levels of protein expression. These glands are the core anatomical components of the toxicoferan venom system, which exists in myriad points along an evolutionary continuum. Neofunctionalisation of toxins is facilitated by positive selection at functional hotspots on the ancestral protein and venom proteins have undergone dynamic diversification in helodermatid and varanid lizards as well as advanced snakes. A spectacular point on the venom system continuum is the long-glanded blue coral snake (Calliophis bivirgatus), a specialist feeder that preys on fast moving, venomous snakes which have both a high likelihood of prey escape but also represent significant danger to the predator itself. The maxillary venom glands of C. bivirgatus extend one quarter of the snake's body length and nestle within the rib cavity. Despite the snake's notoriety its venom has remained largely unstudied. Here we show that the venom uniquely produces spastic paralysis, in contrast to the flaccid paralysis typically produced by neurotoxic snake venoms. The toxin responsible, which we have called calliotoxin (δ-elapitoxin-Cb1a), is a three-finger toxin (3FTx). Calliotoxin shifts the voltage-dependence of NaV1.4 activation to more hyperpolarised potentials, inhibits inactivation, and produces large ramp currents, consistent with its profound effects on contractile force in an isolated skeletal muscle preparation. Voltage-gated sodium channels (NaV) are a particularly attractive pharmacological target as they are involved in almost all physiological processes including action potential generation and conduction. Accordingly, venom peptides that interfere with NaV function provide a key defensive and predatory advantage to a range of invertebrate venomous species including cone snails, scorpions, spiders, and anemones. Enhanced activation or delayed inactivation of sodium channels by toxins is associated with the extremely rapid onset of tetanic/excitatory paralysis in envenomed prey animals. A strong selection pressure exists for the evolution of such toxins where there is a high chance of prey escape. However, despite their prevalence in other venomous species, toxins causing delay of sodium channel inhibition have never previously been described in vertebrate venoms. Here we show that NaV modulators, convergent with those of invertebrates, have evolved in the venom of the long-glanded coral snake. Calliotoxin represents a functionally novel class of 3FTx and a structurally novel class of NaV toxins that will provide significant insights into the pharmacology and physiology of NaV. The toxin represents a remarkable case of functional convergence between invertebrate and vertebrate venom systems in response to similar selection pressures. These results underscore the dynamic evolution of the Toxicofera reptile system and reinforces the value of using evolution as a roadmap for biodiscovery.

Canopy Venom: Proteomic Comparison among New World Arboreal Pit-Viper Venoms

Central and South American pitvipers, belonging to the genera Bothrops and Bothriechis, have independently evolved arboreal tendencies. Little is known regarding the composition and activity of their venoms. In order to close this knowledge gap, venom proteomics and toxin activity of species of Bothriechis, and Bothrops (including Bothriopsis) were investigated through established analytical methods. A combination of proteomics and bioactivity techniques was used to demonstrate a similar diversification of venom composition between large and small species within Bothriechis and Bothriopsis. Increasing our understanding of the evolution of complex venom cocktails may facilitate future biodiscoveries.

Prediction of Toxin Genes from Chinese Yellow Catfish Based on Transcriptomic and Proteomic Sequencing

Fish venom remains a virtually untapped resource. There are so few fish toxin sequences for reference, which increases the difficulty to study toxins from venomous fish and to develop efficient and fast methods to dig out toxin genes or proteins. Here, we utilized Chinese yellow catfish (Pelteobagrus fulvidraco) as our research object, since it is a representative species in Siluriformes with its venom glands embedded in the pectoral and dorsal fins. In this study, we set up an in-house toxin database and a novel toxin-discovering protocol to dig out precise toxin genes by combination of transcriptomic and proteomic sequencing. Finally, we obtained 15 putative toxin proteins distributed in five groups, namely Veficolin, Ink toxin, Adamalysin, Za2G and CRISP toxin. It seems that we have developed a novel bioinformatics method, through which we could identify toxin proteins with high confidence. Meanwhile, these toxins can also be useful for comparative studies in other fish and development of potential drugs.

Gene expression profiling of the venom gland from the Venezuelan mapanare (Bothrops colombiensis) using expressed sequence tags (ESTs)

BACKGROUND

Bothrops colombiensis is a highly dangerous pit viper and responsible for over 70% of snakebites in Venezuela. Although the composition in B. colombiensis venom has been identified using a proteome analysis, the venom gland transcriptome is currently lacking.

RESULTS

We constructed a cDNA library from the venom gland of B. colombiensis, and a set of 729 high quality expressed sequence tags (ESTs) was identified. A total number of 344 ESTs (47.2% of total ESTs) was related to toxins. The most abundant toxin transcripts were metalloproteinases (37.5%), phospholipases A2s (PLA2, 29.7%), and serine proteinases (11.9%). Minor toxin transcripts were linked to waprins (5.5%), C-type lectins (4.1%), ATPases (2.9%), cysteine-rich secretory proteins (CRISP, 2.3%), snake venom vascular endothelium growth factors (svVEGF, 2.3%), L-amino acid oxidases (2%), and other putative toxins (1.7%). While 160 ESTs (22% of total ESTs) coded for translation proteins, regulatory proteins, ribosomal proteins, elongation factors, release factors, metabolic proteins, and immune response proteins. Other proteins detected in the transcriptome (87 ESTs, 11.9% of total ESTs) were undescribed proteins with unknown functions. The remaining 138 (18.9%) cDNAs had no match with known GenBank accessions.

CONCLUSION

This study represents the analysis of transcript expressions and provides a physical resource of unique genes for further study of gene function and the development of novel molecules for medical applications.

Lineage-specific gene radiations underlie the evolution of novel betalain pigmentation in Caryophyllales

Betalain pigments are unique to the Caryophyllales and structurally and biosynthetically distinct from anthocyanins. Two key enzymes within the betalain synthesis pathway have been identified: 4,5-dioxygenase (DODA) that catalyzes the formation of betalamic acid and CYP76AD1, a cytochrome P450 gene that catalyzes the formation of cyclo-DOPA. We performed phylogenetic analyses to reveal the evolutionary history of the DODA and CYP76AD1 lineages and in the context of an ancestral reconstruction of pigment states we explored the evolution of these genes in relation to the complex evolution of pigments in Caryophylalles. Duplications within the CYP76AD1 and DODA lineages arose just before the origin of betalain pigmentation in the core Caryophyllales. The duplications gave rise to DODA-α and CYP76AD1-α isoforms that appear specific to betalain synthesis. Both betalain-specific isoforms were then lost or downregulated in the anthocyanic Molluginaceae and Caryophyllaceae. Our findings suggest a single origin of the betalain synthesis pathway, with neofunctionalization following gene duplications in the CYP76AD1 and DODA lineages. Loss of DODA-α and CYP76AD1-α in anthocyanic taxa suggests that betalain pigmentation has been lost twice in Caryophyllales, and exclusion of betalain pigments from anthocyanic taxa is mediated through gene loss or downregulation. [Correction added after online publication 13 May 2015: in the last two paragraphs of the Summary the gene name CYP761A was changed to CYP76AD1.].

Why do we study animal toxins?

Venom (toxins) is an important trait evolved along the evolutionary tree of animals. Our knowledges on venoms, such as their origins and loss, the biological relevance and the coevolutionary patterns with other organisms are greatly helpful in understanding many fundamental biological questions, i.e., the environmental adaptation and survival competition, the evolution shaped development and balance of venoms, and the sophisticated correlations among venom, immunity, body power, intelligence, their genetic basis, inherent association, as well as the cost-benefit and trade-offs of biological economy. Lethal animal envenomation can be found worldwide. However, from foe to friend, toxin studies have led lots of important discoveries and exciting avenues in deciphering and fighting human diseases, including the works awarded the Nobel Prize and lots of key clinic therapeutics. According to our survey, so far, only less than 0.1% of the toxins of the venomous animals in China have been explored. We emphasize on the similarities shared by venom and immune systems, as well as the studies of toxin knowledge-based physiological toxin-like proteins/peptides (TLPs). We propose the natural pairing hypothesis. Evolution links toxins with humans. Our mission is to find out the right natural pairings and interactions of our body elements with toxins, and with endogenous toxin-like molecules. Although, in nature, toxins may endanger human lives, but from a philosophical point of view, knowing them well is an effective way to better understand ourselves. So, this is why we study toxins.

Fossilized venom: the unusually conserved venom profiles of Heloderma species (beaded lizards and gila monsters)

Research into snake venoms has revealed extensive variation at all taxonomic levels. Lizard venoms, however, have received scant research attention in general, and no studies of intraclade variation in lizard venom composition have been attempted to date. Despite their iconic status and proven usefulness in drug design and discovery, highly venomous helodermatid lizards (gila monsters and beaded lizards) have remained neglected by toxinological research. Proteomic comparisons of venoms of three helodermatid lizards in this study has unravelled an unusual similarity in venom-composition, despite the long evolutionary time (~30 million years) separating H. suspectum from the other two species included in this study (H. exasperatum and H. horridum). Moreover, several genes encoding the major helodermatid toxins appeared to be extremely well-conserved under the influence of negative selection (but with these results regarded as preliminary due to the scarcity of available sequences). While the feeding ecologies of all species of helodermatid lizard are broadly similar, there are significant morphological differences between species, which impact upon relative niche occupation.

Evolution of receptors for peptides similar to glucagon

The genes encoding the peptide precursors for glucagon (GCG), glucose-dependent insulinotropic peptide (GIP), and ortholog of exendin belong to the same family as shown by sequence similarity. The peptides similar to glucagon encoded by these genes signal through a closely related subfamily of G-protein coupled receptors. A total of five types of genes for receptors for these peptides have been identified, three for the products of GCG (GCGR, GLP1R, and GLP2R) and one each for the products of GIP (GIPR) and the ortholog of exendin (Grlr). Phylogenetic and genomic neighborhood analyses clearly show that these genes originated very early in vertebrate evolution and all were present in the common ancestor of tetrapods and bony fish. Despite their ancient origins, some of these genes are dispensable, with the Glp1r, Gipr, and Grlr being lost on the lineages leading to bony fish, birds, and mammals, respectively. The loss of the genes for these receptors may have been driving forces in the evolution of new functions for these peptides similar to glucagon.

Intraspecific venom variation in the medically significant Southern Pacific Rattlesnake (Crotalus oreganus helleri): biodiscovery, clinical and evolutionary implications

Due to the extreme variation of venom, which consequently results in drastically variable degrees of neutralization by CroFab antivenom, the management and treatment of envenoming by Crotalus oreganus helleri (the Southern Pacific Rattlesnake), one of the most medically significant snake species in all of North America, has been a clinician's nightmare. This snake has also been the subject of sensational news stories regarding supposed rapid (within the last few decades) evolution of its venom. This research demonstrates for the first time that variable evolutionary selection pressures sculpt the intraspecific molecular diversity of venom components in C. o. helleri. We show that myotoxic β-defensin peptides (aka: crotamines/small basic myotoxic peptides) are secreted in large amounts by all populations. However, the mature toxin-encoding nucleotide regions evolve under the constraints of negative selection, likely as a result of their non-specific mode of action which doesn't enforce them to follow the regime of the classic predator-prey chemical arms race. The hemorrhagic and tissue destroying snake venom metalloproteinases (SVMPs) were secreted in larger amounts by the Catalina Island and Phelan rattlesnake populations, in moderate amounts in the Loma Linda population and in only trace levels by the Idyllwild population. Only the Idyllwild population in the San Jacinto Mountains contained potent presynaptic neurotoxic phospholipase A2 complex characteristic of Mohave Rattlesnake (Crotalus scutulatus) and Neotropical Rattlesnake (Crotalus durissus terrificus). The derived heterodimeric lectin toxins characteristic of viper venoms, which exhibit a diversity of biological activities, including anticoagulation, agonism/antagonism of platelet activation, or procoagulation, appear to have evolved under extremely variable selection pressures. While most lectin α- and β-chains evolved rapidly under the influence of positive Darwinian selection, the β-chain lectin of the Catalina Island population appears to have evolved under the constraint of negative selection. Both lectin chains were conspicuously absent in both the proteomics and transcriptomics of the Idyllwild population. Thus, we not only highlight the tremendous biochemical diversity in C. o. helleri's venom-arsenal, but we also show that they experience remarkably variable strengths of evolutionary selection pressures, within each toxin class among populations and among toxin classes within each population. The mapping of geographical venom variation not only provides additional information regarding venom evolution, but also has direct medical implications by allowing prediction of the clinical effects of rattlesnake bites from different regions. Such information, however, also points to these highly variable venoms as being a rich source of novel toxins which may ultimately prove to be useful in drug design and development.

BIOLOGICAL SIGNIFICANCE

These results have direct implications for the treatment of envenomed patients. The variable venom profile of Crotalus oreganus helleri underscores the biodiscovery potential of novel snake venoms.

Venom down under: dynamic evolution of Australian elapid snake toxins

Despite the unparalleled diversity of venomous snakes in Australia, research has concentrated on a handful of medically significant species and even of these very few toxins have been fully sequenced. In this study, venom gland transcriptomes were sequenced from eleven species of small Australian elapid snakes, from eleven genera, spanning a broad phylogenetic range. The particularly large number of sequences obtained for three-finger toxin (3FTx) peptides allowed for robust reconstructions of their dynamic molecular evolutionary histories. We demonstrated that each species preferentially favoured different types of α-neurotoxic 3FTx, probably as a result of differing feeding ecologies. The three forms of α-neurotoxin [Type I (also known as (aka): short-chain), Type II (aka: long-chain) and Type III] not only adopted differential rates of evolution, but have also conserved a diversity of residues, presumably to potentiate prey-specific toxicity. Despite these differences, the different α-neurotoxin types were shown to accumulate mutations in similar regions of the protein, largely in the loops and structurally unimportant regions, highlighting the significant role of focal mutagenesis. We theorize that this phenomenon not only affects toxin potency or specificity, but also generates necessary variation for preventing/delaying prey animals from acquiring venom-resistance. This study also recovered the first full-length sequences for multimeric phospholipase A₂ (PLA₂) ‘taipoxin/paradoxin’ subunits from non-Oxyuranus species, confirming the early recruitment of this extremely potent neurotoxin complex to the venom arsenal of Australian elapid snakes. We also recovered the first natriuretic peptides from an elapid that lack the derived C-terminal tail and resemble the plesiotypic form (ancestral character state) found in viper venoms. This provides supporting evidence for a single early recruitment of natriuretic peptides into snake venoms. Novel forms of kunitz and waprin peptides were recovered, including dual domain kunitz-kunitz precursors and the first kunitz-waprin hybrid precursors from elapid snakes. The novel sequences recovered in this study reveal that the huge diversity of unstudied venomous Australian snakes are of considerable interest not only for the investigation of venom and whole organism evolution but also represent an untapped bioresource in the search for novel compounds for use in drug design and development.

Evolution stings: the origin and diversification of scorpion toxin peptide scaffolds

The episodic nature of natural selection and the accumulation of extreme sequence divergence in venom-encoding genes over long periods of evolutionary time can obscure the signature of positive Darwinian selection. Recognition of the true biocomplexity is further hampered by the limited taxon selection, with easy to obtain or medically important species typically being the subject of intense venom research, relative to the actual taxonomical diversity in nature. This holds true for scorpions, which are one of the most ancient terrestrial venomous animal lineages. The family Buthidae that includes all the medically significant species has been intensely investigated around the globe, while almost completely ignoring the remaining non-buthid families. Australian scorpion lineages, for instance, have been completely neglected, with only a single scorpion species (Urodacus yaschenkoi) having its venom transcriptome sequenced. Hence, the lack of venom composition and toxin sequence information from an entire continent’s worth of scorpions has impeded our understanding of the molecular evolution of scorpion venom. The molecular origin, phylogenetic relationships and evolutionary histories of most scorpion toxin scaffolds remain enigmatic. In this study, we have sequenced venom gland transcriptomes of a wide taxonomical diversity of scorpions from Australia, including buthid and non-buthid representatives. Using state-of-art molecular evolutionary analyses, we show that a majority of CSα/β toxin scaffolds have experienced episodic influence of positive selection, while most non-CSα/β linear toxins evolve under the extreme influence of negative selection. For the first time, we have unraveled the molecular origin of the major scorpion toxin scaffolds, such as scorpion venom single von Willebrand factor C-domain peptides (SV-SVC), inhibitor cystine knot (ICK), disulphide-directed beta-hairpin (DDH), bradykinin potentiating peptides (BPP), linear non-disulphide bridged peptides and antimicrobial peptides (AMP). We have thus demonstrated that even neglected lineages of scorpions are a rich pool of novel biochemical components, which have evolved over millions of years to target specific ion channels in prey animals, and as a result, possess tremendous implications in therapeutics.

Origin and functional diversification of an amphibian defense peptide arsenal

The skin secretion of many amphibians contains an arsenal of bioactive molecules, including hormone-like peptides (HLPs) acting as defense toxins against predators, and antimicrobial peptides (AMPs) providing protection against infectious microorganisms. Several amphibian taxa seem to have independently acquired the genes to produce skin-secreted peptide arsenals, but it remains unknown how these originated from a non-defensive ancestral gene and evolved diverse defense functions against predators and pathogens. We conducted transcriptome, genome, peptidome and phylogenetic analyses to chart the full gene repertoire underlying the defense peptide arsenal of the frog Silurana tropicalis and reconstruct its evolutionary history. Our study uncovers a cluster of 13 transcriptionally active genes, together encoding up to 19 peptides, including diverse HLP homologues and AMPs. This gene cluster arose from a duplicated gastrointestinal hormone gene that attained a HLP-like defense function after major remodeling of its promoter region. Instead, new defense functions, including antimicrobial activity, arose by mutation of the precursor proteins, resulting in the proteolytic processing of secondary peptides alongside the original ones. Although gene duplication did not trigger functional innovation, it may have subsequently facilitated the convergent loss of the original function in multiple gene lineages (subfunctionalization), completing their transformation from HLP gene to AMP gene. The processing of multiple peptides from a single precursor entails a mechanism through which peptide-encoding genes may establish new functions without the need for gene duplication to avoid adaptive conflicts with older ones.

Squeezers and leaf-cutters: differential diversification and degeneration of the venom system in toxicoferan reptiles

Although it has been established that all toxicoferan squamates share a common venomous ancestor, it has remained unclear whether the maxillary and mandibular venom glands are evolving on separate gene expression trajectories or if they remain under shared genetic control. We show that identical transcripts are simultaneously expressed not only in the mandibular and maxillary glands, but also in the enigmatic snake rictal gland. Toxin molecular frameworks recovered in this study were three-finger toxin (3FTx), CRiSP, crotamine (beta-defensin), cobra venom factor, cystatin, epididymal secretory protein, kunitz, L-amino acid oxidase, lectin, renin aspartate protease, veficolin, and vespryn. We also discovered a novel low-molecular weight disulfide bridged peptide class in pythonid snake glands. In the iguanian lizards, the most highly expressed are potentially antimicrobial in nature (crotamine (beta-defensin) and cystatin), with crotamine (beta-defensin) also the most diverse. However, a number of proteins characterized from anguimorph lizards and caenophidian snakes with hemotoxic or neurotoxic activities were recruited in the common toxicoferan ancestor and remain expressed, albeit in low levels, even in the iguanian lizards. In contrast, the henophidian snakes express 3FTx and lectin toxins as the dominant transcripts. Even in the constricting pythonid and boid snakes, where the glands are predominantly mucous-secreting, low-levels of toxin transcripts can be detected. Venom thus appears to play little role in feeding behavior of most iguanian lizards or the powerful constricting snakes, and the low levels of expression argue against a defensive role. However, clearly the incipient or secondarily atrophied venom systems of these taxa may be a source of novel compounds useful in drug design and discovery.

Dracula's children: molecular evolution of vampire bat venom

While vampire bat oral secretions have been the subject of intense research, efforts have concentrated only on two components: DSPA (Desmodus rotundus salivary plasminogen activator) and Draculin. The molecular evolutionary history of DSPA has been elucidated, while conversely draculin has long been known from only a very small fragment and thus even the basic protein class was not even established. Despite the fact that vampire bat venom has a multitude of effects unaccounted by the documented bioactivities of DSPA and draculin, efforts have not been made to establish what other bioactive proteins are secreted by their submaxillary gland. In addition, it has remained unclear whether the anatomically distinct anterior and posterior lobes of the submaxillary gland are evolving on separate gene expression trajectories or if they remain under the shared genetic control. Using a combined proteomic and transcriptomic approach, we show that identical proteins are simultaneously expressed in both lobes. In addition to recovering the known structural classes of DSPA, we recovered a novel DSPA isoform as well as obtained a very large sequence stretch of draculin and thus established that it is a mutated version of the lactotransferrin scaffold. This study reveals a much more complex secretion profile than previously recognised. In addition to obtaining novel versions of scaffolds convergently recruited into other venoms (allergen-like, CRiSP, kallikrein, Kunitz, lysozyme), we also documented novel expression of small peptides related to calcitonin, PACAP, and statherin. Other overexpressed protein types included BPI-fold, lacritin, and secretoglobin. Further, we investigate the molecular evolution of various vampire bat venom-components and highlight the dominant role of positive selection in the evolution of these proteins. Conspicuously many of the proteins identified in the proteome were found to be homologous to proteins with known activities affecting vasodilation and platelet aggregation. We show that vampire bat venom proteins possibly evade host immune response by the mutation of the surface chemistry through focal mutagenesis under the guidance of positive Darwinian selection. These results not only contribute to the body of knowledge regarding haematophagous venoms but also provide a rich resource for novel lead compounds for use in drug design and development.

BIOLOGICAL SIGNIFICANCE

These results have direct implications in understanding the molecular evolutionary history of vampire bat venom. The unusual peptides discovered reinforce the value of studying such neglected taxon for biodiscovery.

Transcriptome analyses of primitively eusocial wasps reveal novel insights into the evolution of sociality and the origin of alternative phenotypes

BACKGROUND

Understanding how alternative phenotypes arise from the same genome is a major challenge in modern biology. Eusociality in insects requires the evolution of two alternative phenotypes - workers, who sacrifice personal reproduction, and queens, who realize that reproduction. Extensive work on honeybees and ants has revealed the molecular basis of derived queen and worker phenotypes in highly eusocial lineages, but we lack equivalent deep-level analyses of wasps and of primitively eusocial species, the latter of which can reveal how phenotypic decoupling first occurs in the early stages of eusocial evolution.

RESULTS

We sequenced 20 Gbp of transcriptomes derived from brains of different behavioral castes of the primitively eusocial tropical paper wasp Polistes canadensis. Surprisingly, 75% of the 2,442 genes differentially expressed between phenotypes were novel, having no significant homology with described sequences. Moreover, 90% of these novel genes were significantly upregulated in workers relative to queens. Differential expression of novel genes in the early stages of sociality may be important in facilitating the evolution of worker behavioral complexity in eusocial evolution. We also found surprisingly low correlation in the identity and direction of expression of differentially expressed genes across similar phenotypes in different social lineages, supporting the idea that social evolution in different lineages requires substantial de novo rewiring of molecular pathways.

CONCLUSIONS

These genomic resources for aculeate wasps and first transcriptome-wide insights into the origin of castes bring us closer to a more general understanding of eusocial evolution and how phenotypic diversity arises from the same genome.

Complex cocktails: the evolutionary novelty of venoms

Venoms have evolved on numerous occasions throughout the animal kingdom. These 'biochemical weapon systems' typically function to facilitate, or protect the producing animal from, predation. Most venomous animals remain unstudied despite venoms providing model systems for investigating predator-prey interactions, molecular evolution, functional convergence, and novel targets for pharmaceutical discovery. Through advances in 'omic' technologies, venom composition data have recently become available for several venomous lineages, revealing considerable complexity in the processes responsible for generating the genetic and functional diversity observed in many venoms. Here, we review these recent advances and highlight the ecological and evolutionary novelty of venom systems.