From genome to proteome: Comprehensive identification of venom toxins from the Chinese funnel-web spider (Macrothelidae: Macrothele yani)

Macrothelidae is a family of mygalomorph spiders containing the extant genera Macrothele and Vacrothele. China is an important center of diversity for Macrothele with 65 % of the known species occurring there. Previous work on Macrothele was able to uncover several important toxin compounds including Raventoxin which may have applications in biomedicine and agricultural chemistry. Despite the importance of Macrothele spiders, high-quality reference genomes are still lacking, which hinders our understanding and application of the toxin compounds. In this study, we assembled the genome of the Macrothele yani to help fill gaps in our understanding of toxin biology in this lineage of spiders to encourage the future study and applications of these compounds. The final assembled genome was 6.79 Gb in total length, had a contig N50 of 21.44 Mb, and scaffold N50 of 156.16 Mb. Hi-C scaffolding assigned 98.19 % of the genome to 46 pseudo-chromosomes with a BUSCO score of 95.7 % for the core eukaryotic gene set. The assembled genome was found to contain 75.62 % repetitive DNA and a total of 39,687 protein-coding genes were annotated making it the spider genome with highest number of genes. Through integrated analysis of venom gland transcriptomics and venom proteomics, a total of 194 venom toxins were identified, including 38 disulfide-rich peptide neurotoxins, among which 12 were ICK knottin peptides. In summary, we present the first high-quality genome assembly at the chromosomal level for any Macrothelidae spider, filling an important gap in our knowledge of these spiders. Such high-quality genomic data will be invaluable as a reference in resolving Araneae spider phylogenies and in screening different spider species for novel compounds applicable to numerous medical and agricultural applications.

Sea anemones, methylmercury, and bacterial infection: A closer look at multiple stressors

Specimens of the Mediterranean sea anemone Anemonia viridis were exposed to methylmercury (MeHg) and bacterial infection to study their immune responses to a well-known toxic pollutant. Anemones were housed in laboratory conditions and divided into five experimental groups: 1. control (no microinjection); 2. filtered seawater + buffer injection; 3. filtered seawater + Escherichia coli injection; 4. MeHg + buffer injection; 5. MeHg + E. coli injection. Data showed an increase in antioxidant enzyme production compared to the constitutive condition, while methylmercury inhibited lysozyme production. The buffer inoculation had no statistically significant effects on the animals. In addition, electrophoretic and protease analyses revealed differences in the type of proteins produced, as well as a modulation of proteases depending on the treatment. The study demonstrated the immunomodulatory effect of the organic pollutant on A. viridis, validating its use as a model organism for marine coastal biomonitoring programmes and multiple stress studies.

Evolutionary Analysis of Cnidaria Small Cysteine-Rich Proteins (SCRiPs), an Enigmatic Neurotoxin Family from Stony Corals and Sea Anemones (Anthozoa: Hexacorallia)

Cnidarians (corals, sea anemones, and jellyfish) produce toxins that play central roles in key ecological processes, including predation, defense, and competition, being the oldest extant venomous animal lineage. Cnidaria small cysteine-rich proteins (SCRiPs) were the first family of neurotoxins detected in stony corals, one of the ocean's most crucial foundation species. Yet, their molecular evolution remains poorly understood. Moreover, the lack of a clear classification system has hindered the establishment of an accurate and phylogenetically informed nomenclature. In this study, we extensively surveyed 117 genomes and 103 transcriptomes of cnidarians to identify orthologous SCRiP gene sequences. We annotated a total of 168 novel putative SCRiPs from over 36 species of stony corals and 12 species of sea anemones. Phylogenetic reconstruction identified four distinct SCRiP subfamilies, according to strict discrimination criteria based on well-supported monophyly with a high percentage of nucleotide and amino acids' identity. Although there is a high prevalence of purifying selection for most SCRiP subfamilies, with few positively selected sites detected, a subset of Acroporidae sequences is influenced by diversifying positive selection, suggesting potential neofunctionalizations related to the fine-tuning of toxin potency. We propose a new nomenclature classification system relying on the phylogenetic distribution and evolution of SCRiPs across Anthozoa, which will further assist future proteomic and functional research efforts.

Metatranscriptome analysis reveals the putative venom toxin repertoire of the biofouling hydroid Ectopleura larynx

Cnidarians thriving in biofouling communities on aquaculture net pens represent a significant health risk for farmed finfish due to their stinging cells. The toxins coming into contact with the fish, during net cleaning, can adversely affect their behavior, welfare, and survival, with a particularly serious health risk for the gills, causing direct tissue damage such as formation of thrombi and increasing risks of secondary infections. The hydroid Ectopleura larynx is one of the most common fouling organisms in Northern Europe. However, despite its significant economic, environmental, and operational impact on finfish aquaculture, biological information on this species is scarce and its venom composition has never been investigated. In this study, we generated a whole transcriptome of E. larynx, and identified its putative expressed venom toxin proteins (predicted toxin proteins, not functionally characterized) based on in silico transcriptome annotation mining and protein sequence analysis. The results uncovered a broad and diverse repertoire of putative toxin proteins for this hydroid species. Its toxic arsenal appears to include a wide and complex selection of toxin proteins, covering a large panel of potential biological functions that play important roles in envenomation. The putative toxins identified in this species, such as neurotoxins, GTPase toxins, metalloprotease toxins, ion channel impairing toxins, hemorrhagic toxins, serine protease toxins, phospholipase toxins, pore-forming toxins, and multifunction toxins may cause various major deleterious effects in prey, predators, and competitors. These results provide valuable new insights into the venom composition of cnidarians, and venomous marine organisms in general, and offer new opportunities for further research into novel and valuable bioactive molecules for medicine, agronomics and biotechnology.

Microbiota regulates life-cycle transition and nematocyte dynamics in jellyfish

Jellyfish represent one of the most basal animal groups with complex life cycles. The polyp-to-medusa transition, termed strobilation, is the pivotal process that determines the switch in swimming behavior and jellyfish blooms. Their microbiota plays an essential role in strobilation. Here, we investigated microbiota-mediated host phenotype dynamics during strobilation in the jellyfish Aurelia coerulea via antibiotic-induced microbiome alteration. Microbial depletion delayed the initiation of strobilation and resulted in fewer segments and ephyrae, which could be restored via microbial recolonization. Jellyfish-associated cyanobacteria, which were eliminated by antibiotics in the polyp stage, had the potential to supply retinal and trigger the retinoic acid signaling cascade, which drove the strobilation process. The microbiota regulated nematocyte development and differentiation, influencing the feeding and growth of the jellyfish. The findings improve our understanding of jellyfish-microbe interactions and provide new insights into the role of the microbiota in shaping feeding behavior through nematocyte dynamics.

An ancient pan-cnidarian microRNA regulates stinging capsule biogenesis in Nematostella vectensis

An ancient evolutionary innovation of a novel cell type, the stinging cell (cnidocyte), appeared >600 million years ago in the phylum Cnidaria (sea anemones, corals, hydroids, and jellyfish). A complex bursting nano-injector of venom, the cnidocyst, is embedded in cnidocytes and enables cnidarians to paralyze their prey and predators, contributing to this phylum's evolutionary success. In this work, we show that post-transcriptional regulation by a pan-cnidarian microRNA, miR-2022, is essential for biogenesis of these cells in the sea anemone Nematostella vectensis. By manipulation of miR-2022 levels in a transgenic reporter line of cnidocytes, followed by transcriptomics, single-cell data analysis, prey paralysis assays, and cell sorting of transgenic cnidocytes, we reveal that miR-2022 enables cnidocyte biogenesis in Nematostella, while exhibiting a conserved expression domain with its targets in cnidocytes of other cnidarian species. Thus, here we revealed a functional basis to the conservation of one of nature's most ancient microRNAs.

Genomic, functional and structural analyses elucidate evolutionary innovation within the sea anemone 8 toxin family

BACKGROUND

The ShK toxin from Stichodactyla helianthus has established the therapeutic potential of sea anemone venom peptides, but many lineage-specific toxin families in Actiniarians remain uncharacterised. One such peptide family, sea anemone 8 (SA8), is present in all five sea anemone superfamilies. We explored the genomic arrangement and evolution of the SA8 gene family in Actinia tenebrosa and Telmatactis stephensoni, characterised the expression patterns of SA8 sequences, and examined the structure and function of SA8 from the venom of T. stephensoni.

RESULTS

We identified ten SA8-family genes in two clusters and six SA8-family genes in five clusters for T. stephensoni and A. tenebrosa, respectively. Nine SA8 T. stephensoni genes were found in a single cluster, and an SA8 peptide encoded by an inverted SA8 gene from this cluster was recruited to venom. We show that SA8 genes in both species are expressed in a tissue-specific manner and the inverted SA8 gene has a unique tissue distribution. While the functional activity of the SA8 putative toxin encoded by the inverted gene was inconclusive, its tissue localisation is similar to toxins used for predator deterrence. We demonstrate that, although mature SA8 putative toxins have similar cysteine spacing to ShK, SA8 peptides are distinct from ShK peptides based on structure and disulfide connectivity.

CONCLUSIONS

Our results provide the first demonstration that SA8 is a unique gene family in Actiniarians, evolving through a variety of structural changes including tandem and proximal gene duplication and an inversion event that together allowed SA8 to be recruited into the venom of T. stephensoni.

Never, Ever Make an Enemy… Out of an Anemone: Transcriptomic Comparison of Clownfish Hosting Sea Anemone Venoms

Sea anemones are predatory marine invertebrates and have diverse venom arsenals. Venom is integral to their biology, and is used in competition, defense, and feeding. Three lineages of sea anemones are known to have independently evolved symbiotic relationships with clownfish, however the evolutionary impact of this relationship on the venom composition of the host is still unknown. Here, we investigate the potential of this symbiotic relationship to shape the venom profiles of the sea anemones that host clownfish. We use transcriptomic data to identify differences and similarities in venom profiles of six sea anemone species, representing the three known clades of clownfish-hosting sea anemones. We recovered 1121 transcripts matching verified toxins across all species, and show that hemolytic and hemorrhagic toxins are consistently the most dominant and diverse toxins across all species examined. These results are consistent with the known biology of sea anemones, provide foundational data on venom diversity of these species, and allow for a review of existing hierarchical structures in venomic studies.

Novel Natural Compounds and Their Anatomical Distribution in the Stinging Fireworm Hermodice carunculata (Annelida)

Increasing evidence in the field of bioprospection fosters the necessity of studying poorly investigated poisonous marine invertebrates to expand knowledge on animal venom biology. Among marine annelids, amphinomid fireworms are notorious for their bearded trunk equipped with a powerful stinging capacity. Here, a methodological workflow based on analytical chemistry techniques (compound isolation followed by mass spectrometry and spectroscopy analyses) was applied to gain new insights, leading to the identification and structural elucidation of an array of natural products from Mediterranean specimens of Hermodice carunculata. Eight betaine-derived unprecedented compounds, named “carunculines”, were detected, bearing two terminal ammonium groups tri-and disubstituted at the Cα (A, B) and a series of different alkyl chains (I–VIII). The mixture of chemicals was found in all the body parts of H. carunculata, supporting a mechanism of action triggered by their vehiculation inside the dorsal chaetae, and subsequent injection when chaetae break off on contact. Preliminary investigations to understand adaptive features were also performed, showing a trend in carunculine abundance that fits into the evolutionary history of these worms. These findings shed light on the chemical ecology of amphinomids, giving reasons for the success of H. carunculata in benthic environments and providing promising novel metabolites for biotechnological implications.

Expression profiling and cellular localization of myxozoan minicollagens during nematocyst formation and sporogenesis

In free-living cnidarians, minicollagens are major structural components in the biogenesis of nematocysts. Recent sequence mining and proteomic analysis demonstrate that minicollagens are also expressed by myxozoans, a group of evolutionarily ancient cnidarian endoparasites. Nonetheless, the presence and abundance of nematocyst-associated genes/proteins in nematocyst morphogenesis have never been studied in Myxozoa. Here, we report the gene expression profiles of three myxozoan minicollagens, ncol-1, ncol-3, and the recently identified noncanonical ncol-5, during the intrapiscine development of Myxidium lieberkuehni, the myxozoan parasite of the northern pike, Esox lucius. Moreover, we localized the myxozoan-specific minicollagen Ncol-5 in the developing myxosporean stages by Western blotting, immunofluorescence, and immunogold electron microscopy. We found that expression of minicollagens was spatiotemporally restricted to developing nematocysts within the myxospores during sporogenesis. Intriguingly, Ncol-5 is localized in the walls of nematocysts and predominantly in nematocyst tubules. Overall, we demonstrate that despite being significantly reduced in morphology, myxozoans retain structural components associated with nematocyst development in free-living cnidarians. Furthermore, our findings have practical implications for future functional and comparative studies as minicollagens are useful markers of the developmental phase of myxozoan parasites.

Transcriptomic Insights into the Diversity and Evolution of Myxozoa (Cnidaria, Endocnidozoa) Toxin-like Proteins

Myxozoa is a speciose group of endoparasitic cnidarians that can cause severe ecological and economic effects. Their cnidarian affinity is affirmed by genetic relatedness and the presence of nematocysts, historically called “polar capsules”. Previous studies have revealed the presence of toxin-like proteins in myxozoans; however, the diversity and evolution of venom in Myxozoa are not fully understood. Here, we performed a comparative analysis using the newly sequenced transcriptomes of five Myxobolidae species as well as some public datasets. Toxin mining revealed that myxozoans have lost most of their toxin families, while most species retained Kunitz, M12B, and CRISP, which may play a role in endoparasitism. The venom composition of Endocnidozoa (Myxozoa + Polypodium) differs from that of free-living cnidarians and may be influenced by ecological and environmental factors. Phylogenetic analyses showed that toxin families of myxozoans and free-living cnidarians were clustered into different clades. Selection analyses showed that purifying selection was the dominant evolutionary pressure in toxins, while they were still influenced by episodic adaptive selection. This suggests that the potency or specificity of a particular toxin or species might increase. Overall, our findings provide a more comprehensive framework for understanding the diversity and evolution of Myxozoa venoms.

Implications of bleaching on cnidarian venom ecology

Cnidarian bleaching research often focuses on the effects on a cnidarian's physiological health and fitness, whilst little focus has been towards the impacts of these events on their venom ecology. Given the importance of a cnidarian's venom to their survival and the increasing threat of bleaching events, it is important to understand the effects that this threat may have on this important aspect of their ecology as it may have unforeseen impacts on their ability to catch prey and defend themselves. This review aims to explore evidence that suggests that bleaching may impact on each of the key aspects of a cnidarians' venom ecology: cnidae, venom composition, and venom toxicity. Additionally, the resulting energy deficit, compensatory heterotrophic feeding, and increased defensive measures have been highlighted as possible ecological factors driving these changes. Suggestions are also made to guide the success of research in this field into the future, specifically in regards to selecting a study organism, the importance of accurate symbiont and cnidae identification, use of appropriate bleaching methods, determination of bleaching, and animal handling. Ultimately, this review highlights a significant and important gap in our knowledge into how cnidarians are, and will, continue to be impacted by bleaching stress.

•

Information on the effects of bleaching on cnidarian venom ecology is limited.

•

There is evidence to suggest nematocysts, venom composition and venom toxicity may each be impacted by bleaching.

•

Bleaching may result in depleted energy, increased heterotrophy and/or the need for stronger defensive strategies.

•

To fully understand how cnidarians may be impacted by bleaching stress further research in this field is needed.

•

Future studies should consider the model organism and methodologies, thereby minimising indirect confounding effects.

The cnidarian parasite Ceratonova shasta utilizes inherited and recruited venom-like compounds during infection

Background

Cnidarians are the most ancient venomous organisms. They store a cocktail of venom proteins inside unique stinging organelles called nematocysts. When a cnidarian encounters chemical and physical cues from a potential threat or prey animal, the nematocyst is triggered and fires a harpoon-like tubule to penetrate and inject venom into the prey. Nematocysts are present in all Cnidaria, including the morphologically simple Myxozoa, which are a speciose group of microscopic, spore-forming, obligate parasites of fish and invertebrates. Rather than predation or defense, myxozoans use nematocysts for adhesion to hosts, but the involvement of venom in this process is poorly understood. Recent work shows some myxozoans have a reduced repertoire of venom-like compounds (VLCs) relative to free-living cnidarians, however the function of these proteins is not known.

Methods

We searched for VLCs in the nematocyst proteome and a time-series infection transcriptome of Ceratonova shasta, a myxozoan parasite of salmonid fish. We used four parallel approaches to detect VLCs: BLAST and HMMER searches to preexisting cnidarian venom datasets, the machine learning tool ToxClassifier, and structural modeling of nematocyst proteomes. Sequences that scored positive by at least three methods were considered VLCs. We then mapped their time-series expressions in the fish host and analyzed their phylogenetic relatedness to sequences from other venomous animals.

Results

We identified eight VLCs, all of which have closely related sequences in other myxozoan datasets, suggesting a conserved venom profile across Myxozoa, and an overall reduction in venom diversity relative to free-living cnidarians. Expression of the VLCs over the 3-week fish infection varied considerably: three sequences were most expressed at one day post-exposure in the fish’s gills; whereas expression of the other five VLCs peaked at 21 days post-exposure in the intestines, coinciding with the formation of mature parasite spores with nematocysts. Expression of VLC genes early in infection, prior to the development of nematocysts, suggests venoms in C. shasta have been repurposed to facilitate parasite invasion and proliferation within the host. Molecular phylogenetics suggested some VLCs were inherited from a cnidarian ancestor, whereas others were more closely related to sequences from venomous non-Cnidarian organisms and thus may have gained qualities of venom components via convergent evolution. The presence of VLCs and their differential expression during parasite infection enrich the concept of what functions a “venom” can have and represent targets for designing therapeutics against myxozoan infections.

Quantitative Insights into the Contribution of Nematocysts to the Adaptive Success of Cnidarians Based on Proteomic Analysis

Nematocysts are secretory organelles in cnidarians that play important roles in predation, defense, locomotion, and host invasion. However, the extent to which nematocysts contribute to adaptation and the mechanisms underlying nematocyst evolution are unclear. Here, we investigated the role of the nematocyst in cnidarian evolution based on eight nematocyst proteomes and 110 cnidarian transcriptomes/genomes. We detected extensive species-specific adaptive mutations in nematocyst proteins (NEMs) and evidence for decentralized evolution, in which most evolutionary events involved non-core NEMs, reflecting the rapid diversification of NEMs in cnidarians. Moreover, there was a 33-55 million year macroevolutionary lag between nematocyst evolution and the main phases of cnidarian diversification, suggesting that the nematocyst can act as a driving force in evolution. Quantitative analysis revealed an excess of adaptive changes in NEMs and enrichment for positively selected conserved NEMs. Together, these findings suggest that nematocysts may be key to the adaptive success of cnidarians and provide a reference for quantitative analyses of the roles of phenotypic novelties in adaptation.

Deep-Sea Anemones Are Prospective Source of New Antimicrobial and Cytotoxic Compounds

The peculiarities of the survival and adaptation of deep-sea organisms raise interest in the study of their metabolites as promising drugs. In this work, the hemolytic, cytotoxic, antimicrobial, and enzyme-inhibitory activities of tentacle extracts from five species of sea anemones (Cnidaria, orders Actiniaria and Corallimorpharia) collected near the Kuril and Commander Islands of the Far East of Russia were evaluated for the first time. The extracts of Liponema brevicorne and Actinostola callosa demonstrated maximal hemolytic activity, while high cytotoxic activity against murine splenocytes and Ehrlich carcinoma cells was found in the extract of Actinostola faeculenta. The extracts of Corallimorphus cf. pilatus demonstrated the greatest activity against Ehrlich carcinoma cells but were not toxic to mouse spleen cells. Sea anemones C. cf. pilatus and Stomphia coccinea are promising sources of antimicrobial and antifungal compounds, being active against Gram-positive bacteria Bacillus subtilis, Staphylococcus aureus, and yeast Candida albicans. Moreover, all sea anemones contain α-galactosidase inhibitors. Peptide mass fingerprinting of L. brevicorne and C. cf. pilatus extracts provided a wide range of peptides, predominantly with molecular masses of 4000–5900 Da, which may belong to a known or new structural class of toxins. The obtained data allow concluding that deep-sea anemones are a promising source of compounds for drug discovery.

Phylogenetic and Selection Analysis of an Expanded Family of Putatively Pore-Forming Jellyfish Toxins (Cnidaria: Medusozoa)

Many jellyfish species are known to cause a painful sting, but box jellyfish (class Cubozoa) are a well-known danger to humans due to exceptionally potent venoms. Cubozoan toxicity has been attributed to the presence and abundance of cnidarian-specific pore-forming toxins called jellyfish toxins (JFTs), which are highly hemolytic and cardiotoxic. However, JFTs have also been found in other cnidarians outside of Cubozoa, and no comprehensive analysis of their phylogenetic distribution has been conducted to date. Here, we present a thorough annotation of JFTs from 147 cnidarian transcriptomes and document 111 novel putative JFTs from over 20 species within Medusozoa. Phylogenetic analyses show that JFTs form two distinct clades, which we call JFT-1 and JFT-2. JFT-1 includes all known potent cubozoan toxins, as well as hydrozoan and scyphozoan representatives, some of which were derived from medically relevant species. JFT-2 contains primarily uncharacterized JFTs. Although our analyses detected broad purifying selection across JFTs, we found that a subset of cubozoan JFT-1 sequences are influenced by gene-wide episodic positive selection compared with homologous toxins from other taxonomic groups. This suggests that duplication followed by neofunctionalization or subfunctionalization as a potential mechanism for the highly potent venom in cubozoans. Additionally, published RNA-seq data from several medusozoan species indicate that JFTs are differentially expressed, spatially and temporally, between functionally distinct tissues. Overall, our findings suggest a complex evolutionary history of JFTs involving duplication and selection that may have led to functional diversification, including variability in toxin potency and specificity.

The myxozoan minicollagen gene repertoire was not simplified by the parasitic lifestyle: computational identification of a novel myxozoan minicollagen gene

BACKGROUND

Lineage-specific gene expansions represent one of the driving forces in the evolutionary dynamics of unique phylum traits. Myxozoa, a cnidarian subphylum of obligate parasites, are evolutionarily altered and highly reduced organisms with a simple body plan including cnidarian-specific organelles and polar capsules (a type of nematocyst). Minicollagens, a group of structural proteins, are prominent constituents of nematocysts linking Myxozoa and Cnidaria. Despite recent advances in the identification of minicollagens in Myxozoa, the evolutionary history and diversity of minicollagens in Myxozoa and Cnidaria remain elusive.

RESULTS

We generated new transcriptomes of two myxozoan species using a novel pipeline for filtering of closely related contaminant species in RNA-seq data. Mining of our transcriptomes and published omics data confirmed the existence of myxozoan Ncol-4, reported only once previously, and revealed a novel noncanonical minicollagen, Ncol-5, which is exclusive to Myxozoa. Phylogenetic analyses support a close relationship between myxozoan Ncol-1-3 with minicollagens of Polypodium hydriforme, but suggest independent evolution in the case of the myxozoan minicollagens Ncol-4 and Ncol-5. Additional genome- and transcriptome-wide searches of cnidarian minicollagens expanded the dataset to better clarify the evolutionary trajectories of minicollagen.

CONCLUSIONS

The development of a new approach for the handling of next-generation data contaminated by closely related species represents a useful tool for future applications beyond the field of myxozoan research. This data processing pipeline allowed us to expand the dataset and study the evolution and diversity of minicollagen genes in Myxozoa and Cnidaria. We identified a novel type of minicollagen in Myxozoa (Ncol-5). We suggest that the large number of minicollagen paralogs in some cnidarians is a result of several recent large gene multiplication events. We revealed close juxtaposition of minicollagens Ncol-1 and Ncol-4 in myxozoan genomes, suggesting their common evolutionary history. The unique gene structure of myxozoan Ncol-5 suggests a specific function in the myxozoan polar capsule or tubule. Despite the fact that myxozoans possess only one type of nematocyst, their gene repertoire is similar to those of other cnidarians.

The venom proteome of three common scyphozoan jellyfishes (Chrysaora caliparea, Cyanea nozakii and Lychnorhiza malayensis) (Cnidaria: Scyphozoa) from the coastal waters of India

The jellyfish venom stored in nematocysts contains highly toxic compounds comprising of polypeptides, enzymes and other proteins, which form their chemical defence armoury against predators. We have characterized the proteome of crude venom extract from three bloom-forming scyphozoan jellyfish along the south-west coast of India, Chrysaora caliparea, Cyanea nozakii and Lychnorhiza malayensis using a Quadrupole-Time of Flight (Q/TOF) mass spectrometry analysis. The most abundant toxin identified from Chrysaora caliparea and Lychnorhiza malayensis is similar to the pore-forming toxins and metalloproteinases. A protective antioxidant enzyme called peroxiredoxin was found abundantly in Cyanea nozakii. Metalloproteinase identified from the C. caliparea shows similarity with the venom of pit viper (Bothrops pauloensis), while that of L. malayensis was similar to the venom of snakes such as the Bothrops insularis and Bothrops asper. Kininogen-1 is a secreted protein, identified for the first time from the jellyfish L. malayensis. The proteome analysis of Cyanea nozakii, Chrysaora caliparea and Lychnorhiza malayensis contained 20, 12, 8 unique proteins, respectively. Our study characterized the proteome map of crude venom extract from L. malayensis and C. caliparea for the first time, and the venom profile is compared with published information elsewhere. Proteomic data from this study has been made available in the public domain.

Conservation and turnover of miRNAs and their highly complementary targets in early branching animals

MicroRNAs (miRNAs) are crucial post-transcriptional regulators that have been extensively studied in Bilateria, a group comprising the majority of extant animals, where more than 30 conserved miRNA families have been identified. By contrast, bilaterian miRNA targets are largely not conserved. Cnidaria is the sister group to Bilateria and thus provides a unique opportunity for comparative studies. Strikingly, like their plant counterparts, cnidarian miRNAs have been shown to predominantly have highly complementary targets leading to transcript cleavage by Argonaute proteins. Here, we assess the conservation of miRNAs and their targets by small RNA sequencing followed by miRNA target prediction in eight species of Anthozoa (sea anemones and corals), the earliest-branching cnidarian class. We uncover dozens of novel miRNAs but only a few conserved ones. Further, given their high complementarity, we were able to computationally identify miRNA targets in each species. Besides evidence for conservation of specific miRNA target sites, which are maintained between sea anemones and stony corals across 500 Myr of evolution, we also find indications for convergent evolution of target regulation by different miRNAs. Our data indicate that cnidarians have only few conserved miRNAs and corresponding targets, despite their high complementarity, suggesting a high evolutionary turnover.

Insights into how development and life-history dynamics shape the evolution of venom

Venomous animals are a striking example of the convergent evolution of a complex trait. These animals have independently evolved an apparatus that synthesizes, stores, and secretes a mixture of toxic compounds to the target animal through the infliction of a wound. Among these distantly related animals, some can modulate and compartmentalize functionally distinct venoms related to predation and defense. A process to separate distinct venoms can occur within and across complex life cycles as well as more streamlined ontogenies, depending on their life-history requirements. Moreover, the morphological and cellular complexity of the venom apparatus likely facilitates the functional diversity of venom deployed within a given life stage. Intersexual variation of venoms has also evolved further contributing to the massive diversity of toxic compounds characterized in these animals. These changes in the biochemical phenotype of venom can directly affect the fitness of these animals, having important implications in their diet, behavior, and mating biology. In this review, we explore the current literature that is unraveling the temporal dynamics of the venom system that are required by these animals to meet their ecological functions. These recent findings have important consequences in understanding the evolution and development of a convergent complex trait and its organismal and ecological implications.

A disulfide-stabilised helical hairpin fold in acrorhagin I: An emerging structural motif in peptide toxins

Acrorhagin I (U-AITX-Aeq5a) is a disulfide-rich peptide identified in the aggressive organs (acrorhagi) of the sea anemone Actinia equina. Previous studies (Toxicon 2005, 46:768-74) found that the peptide is toxic in crabs, although the structural and functional properties of acrorhagin I have not been reported. In this work, an Escherichia coli (BL21 strain) expression system was established for the preparation of ¹³C,¹⁵N-labelled acrorhagin I, and the solution structure was determined using NMR spectroscopy. Structurally, acrorhagin I is similar to B-IV toxin from the marine worm Cerebratulus lacteus (PDB id 1VIB), with a well-defined helical hairpin structure stabilised by four intramolecular disulfide bonds. The recombinant peptide was tested in patch-clamp electrophysiology assays against voltage-gated potassium and sodium channels, and in bacterial and fungal growth inhibitory assays and haemolytic assays. Acrorhagin I was not active against any of the ion channels tested and showed no activity in functional assays, indicating that this peptide may possess a different biological function. Metal ion interaction studies using NMR spectroscopy showed that acrorhagin I bound zinc and nickel, suggesting that its function might be modulated by metal ions or that it may be involved in regulating metal ion levels and their transport. The similarity between the structure of acrorhagin I and that of B-IV toxin from a marine worm suggests that this fold may prove to be a recurring motif in disulfide-rich peptides from marine organisms.

Toxin-like neuropeptides in the sea anemone Nematostella unravel recruitment from the nervous system to venom

The sea anemone Nematostella vectensis (Anthozoa, Cnidaria) is a powerful model for characterizing the evolution of genes functioning in venom and nervous systems. Although venom has evolved independently numerous times in animals, the evolutionary origin of many toxins remains unknown. In this work, we pinpoint an ancestral gene giving rise to a new toxin and functionally characterize both genes in the same species. Thus, we report a case of protein recruitment from the cnidarian nervous to venom system. The ShK-like1 peptide has a ShKT cysteine motif, is lethal for fish larvae and packaged into nematocysts, the cnidarian venom-producing stinging capsules. Thus, ShK-like1 is a toxic venom component. Its paralog, ShK-like2, is a neuropeptide localized to neurons and is involved in development. Both peptides exhibit similarities in their functional activities: They provoke contraction in Nematostella polyps and are toxic to fish. Because ShK-like2 but not ShK-like1 is conserved throughout sea anemone phylogeny, we conclude that the two paralogs originated due to a Nematostella-specific duplication of a ShK-like2 ancestor, a neuropeptide-encoding gene, followed by diversification and partial functional specialization. ShK-like2 is represented by two gene isoforms controlled by alternative promoters conferring regulatory flexibility throughout development. Additionally, we characterized the expression patterns of four other peptides with structural similarities to studied venom components and revealed their unexpected neuronal localization. Thus, we employed genomics, transcriptomics, and functional approaches to reveal one venom component, five neuropeptides with two different cysteine motifs, and an evolutionary pathway from nervous to venom system in Cnidaria.

A Review of Toxins from Cnidaria

Cnidarians have been known since ancient times for the painful stings they induce to humans. The effects of the stings range from skin irritation to cardiotoxicity and can result in death of human beings. The noxious effects of cnidarian venoms have stimulated the definition of their composition and their activity. Despite this interest, only a limited number of compounds extracted from cnidarian venoms have been identified and defined in detail. Venoms extracted from Anthozoa are likely the most studied, while venoms from Cubozoa attract research interests due to their lethal effects on humans. The investigation of cnidarian venoms has benefited in very recent times by the application of omics approaches. In this review, we propose an updated synopsis of the toxins identified in the venoms of the main classes of Cnidaria (Hydrozoa, Scyphozoa, Cubozoa, Staurozoa and Anthozoa). We have attempted to consider most of the available information, including a summary of the most recent results from omics and biotechnological studies, with the aim to define the state of the art in the field and provide a background for future research.

A tentacle for every occasion: comparing the hunting tentacles and sweeper tentacles, used for territorial competition, in the coral Galaxea fascicularis

Background

Coral reefs are among the most diverse, complex and densely populated marine ecosystems. To survive, morphologically simple and sessile cnidarians have developed mechanisms to catch prey, deter predators and compete with adjacent corals for space, yet the mechanisms underlying these functions are largely unknown. Here, we characterize the histology, toxic activity and gene expression patterns in two different types of tentacles from the scleractinian coral Galaxea fascilcularis – catch tentacles (CTs), used to catch prey and deter predators, and sweeper tentacles (STs), specialized tentacles used for territorial aggression.

Results

STs exhibit more mucocytes and higher expression of mucin genes than CTs, and lack the ectodermal cilia used to deliver food to the mouth and remove debris. STs and CTs also express different sensory rhodopsin-like g-protein coupled receptors, suggesting they may employ different sensory pathways. Each tentacle type has a different complement of stinging cells (nematocytes), and the expression in the two tentacles of genes encoding structural nematocyte proteins suggests the stinging cells develop within the tentacles. CTs have higher neurotoxicity to blowfly larvae and hemolytic activity compared to the STs, consistent with a role in prey capture. In contrast, STs have higher phospholipase A2 activity, which we speculate may have a role in inducing tissue damage during territorial aggression. The expression of genes encoding cytolytic toxins (actinoporins) and phospholipases also differs between the tentacle types.

Conclusions

These results show that the same organism utilizes two distinct tentacle types, each equipped with a different venom apparatus and toxin composition, for prey capture and defense and for territorial aggression.

Transcriptomic Analysis of Four Cerianthid (Cnidaria, Ceriantharia) Venoms

Tube anemones, or cerianthids, are a phylogenetically informative group of cnidarians with complex life histories, including a pelagic larval stage and tube-dwelling adult stage, both known to utilize venom in stinging-cell rich tentacles. Cnidarians are an entirely venomous group that utilize their proteinaceous-dominated toxins to capture prey and defend against predators, in addition to several other ecological functions, including intraspecific interactions. At present there are no studies describing the venom for any species within cerianthids. Given their unique development, ecology, and distinct phylogenetic-placement within Cnidaria, our objective is to evaluate the venom-like gene diversity of four species of cerianthids from newly collected transcriptomic data. We identified 525 venom-like genes between all four species. The venom-gene profile for each species was dominated by enzymatic protein and peptide families, which is consistent with previous findings in other cnidarian venoms. However, we found few toxins that are typical of sea anemones and corals, and furthermore, three of the four species express toxin-like genes closely related to potent pore-forming toxins in box jellyfish. Our study is the first to provide a survey of the putative venom composition of cerianthids and contributes to our general understanding of the diversity of cnidarian toxins.

A comparison of the structure and function of nematocysts in free-living and parasitic cnidarians (Myxozoa)

Myxozoans are obligate parasites that have complex life cycles requiring alternate vertebrate and invertebrate hosts, with transmission via microscopic waterborne spores. Unusually for parasites, they belong to the phylum Cnidaria, alongside thousands of free-living corals, sea anemones, jellyfish and hydrozoans. Their cnidarian affinity is affirmed by genetic relatedness and the presence of nematocysts, historically called "polar capsules" in myxozoan research. Free-living cnidarians utilise this cellular weaponry for defence, predation and adhesion, whereas myxozoans use it to anchor to their hosts as the first step in infection. Despite the ~650 million years of divergence between free-living cnidarians and myxozoans, their nematocysts retain many shared morphological and molecular characters. Both are intra-cellular capsules with a single opening, and contain a coiled, evertable tubule. They are composed of unique nematocyst proteins, nematogalectin and minicollagen, and both likely contain an internal matrix of metal cations covalently bound to the anionic polymer poly-gamma glutamate. The rapid dissociation of this matrix and the resulting increase in internal osmotic potential is the driving force behind tubule elongation during discharge. In this review, we compare the structure and function of nematocysts in Myxozoa and free-living Cnidaria, incorporating recent molecular characterizations. We propose that terminology for homologous myxozoan structures be synonymized with those from other Cnidaria, hence, "polar capsule" as a taxon-specific nematocyst morphotype and "polar filament" as "tubule." Despite taxonomic divergence, genome reduction and an evolution to parasitism, myxozoans maintain nematocysts that are structurally and functionally homologous to those of their free-living cnidarian relatives.

Characterising Functional Venom Profiles of Anthozoans and Medusozoans within Their Ecological Context

This review examines the current state of knowledge regarding toxins from anthozoans (sea anemones, coral, zoanthids, corallimorphs, sea pens and tube anemones). We provide an overview of venom from phylum Cnidaria and review the diversity of venom composition between the two major clades (Medusozoa and Anthozoa). We highlight that the functional and ecological context of venom has implications for the temporal and spatial expression of protein and peptide toxins within class Anthozoa. Understanding the nuances in the regulation of venom arsenals has been made possible by recent advances in analytical technologies that allow characterisation of the spatial distributions of toxins. Furthermore, anthozoans are unique in that ecological roles can be assigned using tissue expression data, thereby circumventing some of the challenges related to pharmacological screening.

"Beyond Primary Sequence"-Proteomic Data Reveal Complex Toxins in Cnidarian Venoms

Venomous animals can deploy toxins for both predation and defense. These dual functions of toxins might be expected to promote the evolution of new venoms and alteration of their composition. Cnidarians are the most ancient venomous animals but our present understanding of their venom diversity is compromised by poor taxon sampling. New proteomic data were therefore generated to characterize toxins in venoms of a staurozoan, a hydrozoan, and an anthozoan. We then used a novel clustering approach to compare venom diversity in cnidarians to other venomous animals. Comparison of the presence or absence of 32 toxin protein families indicated venom composition did not vary widely among the 11 cnidarian species studied. Unsupervised clustering of toxin peptide sequences suggested that toxin composition of cnidarian venoms is just as complex as that in many venomous bilaterians, including marine snakes. The adaptive significance of maintaining a complex and relatively invariant venom remains unclear. Future study of cnidarian venom diversity, venom variation with nematocyst types and in different body regions are required to better understand venom evolution.

Reciprocal transplantation of the heterotrophic coral Tubastraea coccinea (Scleractinia: Dendrophylliidae) between distinct habitats did not alter its venom toxin composition

Tubastraea coccinea is an azooxanthellate coral species recorded in the Indian and Atlantic oceans and is presently widespread in the southwestern Atlantic with an alien status for Brazil. T. coccinea outcompete other native coral species by using a varied repertoire of biological traits. For example, T. coccinea has evolved potent venom capable of immobilizing and digesting zooplankton prey. Diversification and modification of venom toxins can provide potential adaptive benefits to individual fitness, yet acquired alteration of venom composition in cnidarians is poorly understood as the adaptive flexibility affecting toxin composition in these ancient lineages has been largely ignored. We used quantitative high-throughput proteomics to detect changes in toxin expression in clonal fragments of specimens collected and interchanged from two environmentally distinct and geographically separate study sites. Unexpectedly, despite global changes in protein expression, there were no changes in the composition and abundance of toxins from coral fragments recovered from either site, and following clonal transplantation between sites. There were also no apparent changes to the cnidome (cnidae) and gross skeletal or soft tissue morphologies of the specimens. These results suggest that the conserved toxin complexity of T. coccinea co-evolved with innovation of the venom delivery system, and its morphological development and phenotypic expression are not modulated by habitat pressures over short periods of time. The adaptive response of the venom trait to specific predatory regimes, however, necessitates further consideration.

A cadherin switch marks germ layer formation in the diploblastic sea anemone Nematostella vectensis

Morphogenesis is a shape-building process during development of multicellular organisms. During this process, the establishment and modulation of cell-cell contacts play an important role. Cadherins, the major cell adhesion molecules, form adherens junctions connecting epithelial cells. Numerous studies of Bilateria have shown that cadherins are associated with the regulation of cell differentiation, cell shape changes, cell migration and tissue morphogenesis. To date, the role of cadherins in non-bilaterians is unknown. Here, we study the expression and function of two paralogous classical cadherins, Cadherin 1 and Cadherin 3, in a diploblastic animal, the sea anemone Nematostella vectensis We show that a cadherin switch accompanies the formation of germ layers. Using specific antibodies, we show that both cadherins are localized to adherens junctions at apical and basal positions in ectoderm and endoderm. During gastrulation, partial epithelial-to-mesenchymal transition of endodermal cells is marked by stepwise downregulation of Cadherin 3 and upregulation of Cadherin 1. Knockdown experiments show that both cadherins are required for maintenance of tissue integrity and tissue morphogenesis. Thus, both sea anemones and bilaterians use independently duplicated cadherins combinatorially for tissue morphogenesis and germ layer differentiation.

The draft genome of Actinia tenebrosa reveals insights into toxin evolution

Sea anemones have a wide array of toxic compounds (peptide toxins found in their venom) which have potential uses as therapeutics. To date, the majority of studies characterizing toxins in sea anemones have been restricted to species from the superfamily, Actinioidea. No highly complete draft genomes are currently available for this superfamily, however, highlighting our limited understanding of the genes encoding toxins in this important group. Here we have sequenced, assembled, and annotated a draft genome for Actinia tenebrosa. The genome is estimated to be approximately 255 megabases, with 31,556 protein-coding genes. Quality metrics revealed that this draft genome matches the quality and completeness of other model cnidarian genomes, including Nematostella, Hydra, and Acropora. Phylogenomic analyses revealed strong conservation of the Cnidaria and Hexacorallia core-gene set. However, we found that lineage-specific gene families have undergone significant expansion events compared with shared gene families. Enrichment analysis performed for both gene ontologies, and protein domains revealed that genes encoding toxins contribute to a significant proportion of the lineage-specific genes and gene families. The results make clear that the draft genome of A. tenebrosa will provide insight into the evolution of toxins and lineage-specific genes, and provide an important resource for the discovery of novel biological compounds.

Venom Composition Does Not Vary Greatly Between Different Nematocyst Types Isolated from the Primary Tentacles of Olindias sambaquiensis (Cnidaria: Hydrozoa)

In this quantitative proteomics study we determined the variety and relative abundance of toxins present in enriched preparations of two nematocyst types isolated from the primary tentacles of the adult medusa stage of the hydrozoan Olindias sambaquiensis. The two nematocyst types were microbasic mastigophores and microbasic euryteles, and these were recovered from the macerated tentacle tissues by using a differential centrifugation approach. Soluble protein extracts from these nematocysts were tagged with tandem mass tag isobaric labels and putative toxins identified using tandem mass spectrometry coupled with a stringent bioinformatics annotation pipeline. Astonishingly, the venom composition of the two capsule types was nearly identical, and there was also little difference in the comparative abundance of toxins between the two nematocyst preparations. This homogeneity suggested that the same toxin complement was present regardless of the penetrative ability of the nematocyst type. Predicted toxin protein families that constituted the venom closely matched those of the toxic proteome of O. sambaquiensis published four years previously, suggesting that venom composition in this species changes little over time. Retaining an array of different nematocyst types to deliver a single venom, rather than sustaining the high metabolic cost necessary to maintain a dynamically evolving venom, may be more advantageous, given the vastly different interspecific interactions that adult medusa encounter in coastal zones.

Combined transcriptomic and proteomic analysis reveals a diversity of venom-related and toxin-like peptides expressed in the mat anemone Zoanthus natalensis (Cnidaria, Hexacorallia)

Venoms from marine animals have been recognized as a new emerging source of peptide-based therapeutics. Several peptide toxins from sea anemone have been investigated as therapeutic leads or pharmacological tools. Venom complexity should be further highlighted using combined strategies of large-scale sequencing and data analysis which integrated transcriptomics and proteomics to elucidate new proteins or peptides to be compared among species. In this work, transcriptomic and proteomic analyses were combined to identify six groups of expressed peptide toxins in Zoanthus natalensis. These include neurotoxin, hemostatic and hemorrhagic toxin, protease inhibitor, mixed function enzymes, venom auxiliary proteins, allergen peptides, and peptides related to the innate immunity. Molecular docking analysis indicated that one expressed Zoanthus Kunitz-like peptide, ZoaKuz1, could be a voltage-gated potassium channels blocker and, hence, it was selected for functional studies. Functional bioassays revealed that ZoaKuz1 has an intrinsic neuroprotective activity in zebrafish model of Parkinson's disease. Since pharmacological blockade of K_V channels is known to induce neuroprotective effects, ZoaKuz1 holds the potential to be developed in a therapeutic tool to control neural dysfunction by slowing or even halting neurodegeneration mediated by ion-channel hyperactivity.

Screening and Immobilization of Interfacial Esterases from Marine Invertebrates as Promising Biocatalyst Derivatives

Interfacial esterases are useful enzymes in bioconversion and racemic mixture resolution processes. Marine invertebrates are few explored potential sources of these proteins. In this work, aqueous extracts of 41 species of marine invertebrates were screened for esterase, lipase, and phospholipase A activities, being all positive. Five extracts (Stichodactyla helianthus, Condylactis gigantea, Stylocheilus longicauda, Zoanthus pulchellus, and Plexaura homomalla) were selected for their activity values and immobilized on Octyl-Sepharose CL 4B support by interfacial adsorption. The selectivity of this immobilization method for interfacial esterases was evidenced by immobilization percentages ≥ 94% in almost all cases for lipase and phospholipase A activities. Six pharmaceutical-relevant esters (phenylethyl butyrate, ethyl-2-hydroxy-4-phenyl-butanoate, 2-oxyranylmethyl acetate (glycidol acetate), 7-aminocephalosporanic acid, methyl-prostaglandin F_2α, and methyl-6-metoxy-α-methyl-2-naphtalen-acetate -naproxen methyl ester-) were bioconverted by at least three of these biocatalysts, with the lowest conversion percentage of 24%. In addition, three biocatalysts were used in the racemic mixture resolution of three previous compounds. The S. helianthus-derived biocatalyst showed the highest enantiomeric ratios for glycidol acetate (2.67, (S)-selective) and naproxen methyl ester (8.32, (R)-selective), and the immobilized extract of S. longicauda was the most resolutive toward the ethyl-2-hydroxy-4-phenyl-butanoate (8.13, (S)-selective). These results indicate the relevance of such marine interfacial esterases as immobilized biocatalysts for the pharmaceutical industry.

The genome of the giant Nomura's jellyfish sheds light on the early evolution of active predation

BACKGROUND

Unique among cnidarians, jellyfish have remarkable morphological and biochemical innovations that allow them to actively hunt in the water column and were some of the first animals to become free-swimming. The class Scyphozoa, or true jellyfish, are characterized by a predominant medusa life-stage consisting of a bell and venomous tentacles used for hunting and defense, as well as using pulsed jet propulsion for mobility. Here, we present the genome of the giant Nomura's jellyfish (Nemopilema nomurai) to understand the genetic basis of these key innovations.

RESULTS

We sequenced the genome and transcriptomes of the bell and tentacles of the giant Nomura's jellyfish as well as transcriptomes across tissues and developmental stages of the Sanderia malayensis jellyfish. Analyses of the Nemopilema and other cnidarian genomes revealed adaptations associated with swimming, marked by codon bias in muscle contraction and expansion of neurotransmitter genes, along with expanded Myosin type II family and venom domains, possibly contributing to jellyfish mobility and active predation. We also identified gene family expansions of Wnt and posterior Hox genes and discovered the important role of retinoic acid signaling in this ancient lineage of metazoans, which together may be related to the unique jellyfish body plan (medusa formation).

CONCLUSIONS

Taken together, the Nemopilema jellyfish genome and transcriptomes genetically confirm their unique morphological and physiological traits, which may have contributed to the success of jellyfish as early multi-cellular predators.

Identification of a pore-forming protein from sea anemone Anthopleura dowii Verrill (1869) venom by mass spectrometry

Background:

Pore-forming proteins (PFP) are a class of toxins abundant in the venom of sea anemones. Owing to their ability to recognize and permeabilize cell membranes, pore-forming proteins have medical potential in cancer therapy or as biosensors. In the present study, we showed the partial purification and sequencing of a pore-forming protein from Anthopleura dowii Verrill (1869). 17.

Methods:

Cytolytic activity of A. dowii Verrill (1869) venom was determined via hemolysis assay in the erythrocytes of four mammals (sheep, goat, human and rabbit). The cytotoxic activity was analyzed in the human adherent lung carcinoma epithelial cells (A549) by the cytosolic lactate dehydrogenase (LDH) assay, and trypan blue staining. The venom was fractionated via ammonium sulfate precipitation gradient, dialysis, and ion exchange chromatography. The presence of a pore-forming protein in purified fractions was evaluated through hemolytic and cytotoxic assays, and the activity fraction was analyzed using the percent of osmotic protections after polyethylene glycol (PEG) treatment and mass spectrometry. 18.

Results:

The amount of protein at which the venom produced 50% hemolysis (HU₅₀) was determined in hemolysis assays using erythrocytes from sheep (HU₅₀ = 10.7 ± 0.2 μg), goat (HU₅₀ = 13.2 ± 0.3 μg), rabbit (HU₅₀ = 34.7 ± 0.5 μg), and human (HU₅₀ = 25.6 ± 0.6 μg). The venom presented a cytotoxic effect in A549 cells and the protein amount present in the venom responsible for producing 50% death (IC₅₀) was determined using a trypan blue cytotoxicity assay (1.84 ± 0.40 μg/mL). The loss of membrane integrity in the A549 cells caused by the venom was detected by the release of LDH in proportion to the amount of protein. The venom was fractionated; and the fraction with hemolytic and cytotoxic activities was analyzed by mass spectrometry. A pore-forming protein was identified. The cytotoxicity in the A549 cells produced by the fraction containing the pore-forming protein was osmotically protected by PEG-3350 Da molecular mass, which corroborated that the loss of integrity in the plasma membrane was produced via pore formation. 19. Conclusion: A. dowii Verrill (1869) venom contains a pore-forming protein suitable for designing new drugs for cancer therapy.

Modern genomic tools reveal the structural and cellular diversity of cnidarian nervous systems

Cnidarians shared a common ancestor with bilaterians more than 600 million years ago. This sister group relationship gives them an informative phylogenetic position for understanding the fascinating morphological and molecular cell type diversity of bilaterian nervous systems. Moreover, cnidarians display novel features such as endodermal neurogenesis and independently evolved centralizations, which provide a platform for understanding the evolution of nervous system innovations. In recent years, the application of modern genomic tools has significantly advanced our understanding of cnidarian nervous system structure and function. For example, transgenic reporter lines and gene knockdown experiments in several cnidarian species reveal a significant degree of conservation in the neurogenesis gene regulatory program, while single cell RNA sequencing projects are providing a much deeper understanding of cnidarian neural cell type diversity. At the level of neural function, the physiological properties of ion channels have been described and calcium imaging of the nervous system in whole animals has allowed for the identification of neural circuits underlying specific behaviours. Cnidarians have arrived in the modern era of molecular neurobiology and are primed to provide exciting new insights into the early evolution of nervous systems.

Integrating Embryonic Development and Evolutionary History to Characterize Tentacle-Specific Cell Types in a Ctenophore

The origin of novel traits can promote expansion into new niches and drive speciation. Ctenophores (comb jellies) are unified by their possession of a novel cell type: the colloblast, an adhesive cell found only in the tentacles. Although colloblast-laden tentacles are fundamental for prey capture among ctenophores, some species have tentacles lacking colloblasts and others have lost their tentacles completely. We used transcriptomes from 36 ctenophore species to identify gene losses that occurred specifically in lineages lacking colloblasts and tentacles. We cross-referenced these colloblast- and tentacle-specific candidate genes with temporal RNA-Seq during embryogenesis in Mnemiopsis leidyi and found that both sets of candidates are preferentially expressed during tentacle morphogenesis. We also demonstrate significant upregulation of candidates from both data sets in the tentacle bulb of adults. Both sets of candidates were enriched for an N-terminal signal peptide and protein domains associated with secretion; among tentacle candidates we also identified orthologs of cnidarian toxin proteins, presenting tantalizing evidence that ctenophore tentacles may secrete toxins along with their adhesive. Finally, using cell lineage tracing, we demonstrate that colloblasts and neurons share a common progenitor, suggesting the evolution of colloblasts involved co-option of a neurosecretory gene regulatory network. Together these data offer an initial glimpse into the genetic architecture underlying ctenophore cell-type diversity.

Cell type-specific expression profiling unravels the development and evolution of stinging cells in sea anemone

Background

Cnidocytes are specialized cells that define the phylum Cnidaria. They possess an “explosive” organelle called cnidocyst that is important for prey capture and anti-predator defense. An extraordinary morphological and functional complexity of the cnidocysts has inspired numerous studies to investigate their structure and development. However, the transcriptomes of the cells bearing these unique organelles are yet to be characterized, impeding our understanding of the genetic basis of their biogenesis.

Results

In this study, we generated a nematocyte reporter transgenic line of the sea anemone Nematostella vectensis using the CRISPR/Cas9 system. By using a fluorescence-activated cell sorter (FACS), we have characterized cell type-specific transcriptomic profiles of various stages of cnidocyte maturation and showed that nematogenesis (the formation of functional cnidocysts) is underpinned by dramatic shifts in the spatiotemporal gene expression. Among the genes identified as upregulated in cnidocytes were Cnido-Jun and Cnido-Fos1—cnidarian-specific paralogs of the highly conserved c-Jun and c-Fos proteins of the stress-induced AP-1 transcriptional complex. The knockdown of the cnidocyte-specific c-Jun homolog by microinjection of morpholino antisense oligomer results in disruption of normal nematogenesis.

Conclusions

Here, we show that the majority of upregulated genes and enriched biochemical pathways specific to cnidocytes are uncharacterized, emphasizing the need for further functional research on nematogenesis. The recruitment of the metazoan stress-related transcription factor c-Fos/c-Jun complex into nematogenesis highlights the evolutionary ingenuity and novelty associated with the formation of these highly complex, enigmatic, and phyletically unique organelles. Thus, we provide novel insights into the biology, development, and evolution of cnidocytes.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0578-4) contains supplementary material, which is available to authorized users.

A genome wide survey reveals multiple nematocyst-specific genes in Myxozoa

Background

Myxozoa represents a diverse group of microscopic endoparasites whose life cycle involves two hosts: a vertebrate (usually a fish) and an invertebrate (usually an annelid worm). Despite lacking nearly all distinguishing animal characteristics, given that each life cycle stage consists of no more than a few cells, molecular phylogenetic studies have revealed that myxozoans belong to the phylum Cnidaria, which includes corals, sea anemones, and jellyfish. Myxozoa, however, do possess a polar capsule; an organelle that is homologous to the stinging structure unique to Cnidaria: the nematocyst. Previous studies have identified in Myxozoa a number of protein-coding genes that are specific to nematocytes (the cells producing nematocysts) and thus restricted to Cnidaria. Determining which other genes are also homologous with the myxozoan polar capsule genes could provide insight into both the conservation and changes that occurred during nematocyst evolution in the transition to endoparasitism.

Results

Previous studies have examined the phylogeny of two cnidarian-restricted gene families: minicollagens and nematogalectins. Here we identify and characterize seven additional cnidarian-restricted genes in myxozoan genomes using a phylogenetic approach. Four of the seven had never previously been identified as cnidarian-specific and none have been studied in a phylogenetic context. A majority of the proteins appear to be involved in the structure of the nematocyst capsule and tubule. No venom proteins were identified among the cnidarian-restricted genes shared by myxozoans.

Conclusions

Given the highly divergent forms that comprise Cnidaria, obtaining insight into the processes underlying their ancient diversification remains challenging. In their evolutionary transition to microscopic endoparasites, myxozoans lost nearly all traces of their cnidarian ancestry, with the one prominent exception being their nematocysts (or polar capsules). Thus nematocysts, and the genes that code for their structure, serve as rich sources of information to support the cnidarian origin of Myxozoa.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1253-7) contains supplementary material, which is available to authorized users.

Cnidarian peptide neurotoxins: a new source of various ion channel modulators or blockers against central nervous systems disease

Cnidaria provide the largest source of bioactive peptides for new drug development. The venoms contain enzymes, potent pore-forming toxins and neurotoxins. The neurotoxins can immobilize predators rapidly when discharged via modifying sodium-channel-gating or blocking the potassium channel during the repolarization stage. Most cnidarian neurotoxins remain conserved under the strong influence of negative selection. Neuroactive peptides targeting the central nervous system through affinity with ion channels could provide insight leading to drug treatment of neurological diseases, which arise from ion channel dysfunctions. Although marine resources offer thousands of possible peptides, only one peptide derived from Cnidaria: ShK-186, also named dalazatide, has reached the pharmaceutical market. This review focuses on neuroprotective agents derived from cnidarian neurotoxic peptides.

Corals hosting symbiotic hydrozoans are less susceptible to predation and disease

In spite of growing evidence that climate change may dramatically affect networks of interacting species, whether-and to what extent-ecological interactions can mediate species' responses to disturbances is an open question. Here we show how a largely overseen association such as that between hydrozoans and scleractinian corals could be possibly associated with a reduction in coral susceptibility to ever-increasing predator and disease outbreaks. We examined 2455 scleractinian colonies (from both Maldivian and the Saudi Arabian coral reefs) searching for non-random patterns in the occurrence of hydrozoans on corals showing signs of different health conditions (i.e. bleaching, algal overgrowth, corallivory and different coral diseases). We show that, after accounting for geographical, ecological and co-evolutionary factors, signs of disease and corallivory are significantly lower in coral colonies hosting hydrozoans than in hydrozoan-free ones. This finding has important implications for our understanding of the ecology of coral reefs, and for their conservation in the current scenario of global change, because it suggests that symbiotic hydrozoans may play an active role in protecting their scleractinian hosts from stresses induced by warming water temperatures.

Evidence for an Alternative Mechanism of Toxin Production in the Box Jellyfish Alatina alata

Cubozoans (box jellyfish) have a reputation as the most venomous animals on the planet. Herein, we provide a review of cubozoan prey capture and digestion informed by the scientific literature. Like all cnidarians, box jellyfish envenomation originates from structures secreted within nematocyte post-Golgi vesicles called nematocysts. When tentacles come in contact with prey or would-be predators, a cocktail of toxins is rapidly deployed from nematocysts via a long spiny tubule that serves to immobilize the target organism. The implication has long been that toxin peptides and proteins making up the venom within the nematocyst capsule are secreted directly by nematocytes during nematogenesis. However, our combined molecular and morphological analysis of the venomous box jellyfish Alatina alata suggests that gland cells with possible dual roles in secreting toxins and toxic-like enzymes are found in the gastric cirri. These putative gland cell assemblages might be functionally important internally (digestion of prey) as well as externally (envenomation) in cubozoans. Despite the absence of nematocysts in the gastric cirri of mature A. alata medusae, this area of the digestive system appears to be the region of the body where venom-implicated gene products are found in highest abundance, challenging the idea that in cnidarians venom is synthesized exclusively in, or nearby, nematocysts. In an effort to uncover evidence for a central area enriched in gland cells associated with the gastric cirri we provide a comparative description of the morphology of the digestive structures of A. alata and Carybdea box jellyfish species. Finally, we conduct a multi-faceted analysis of the gene ontology terms associated with venom-implicated genes expressed in the tentacle/pedalium and gastric cirri, with a particular emphasis on zinc metalloprotease homologs and genes encoding other bioactive proteins that are abundant in the A. alata transcriptome.

Impact of Scyphozoan Venoms on Human Health and Current First Aid Options for Stings

Cnidaria include the most venomous animals of the world. Among Cnidaria, Scyphozoa (true jellyfish) are ubiquitous, abundant, and often come into accidental contact with humans and, therefore, represent a threat for public health and safety. The venom of Scyphozoa is a complex mixture of bioactive substances—including thermolabile enzymes such as phospholipases, metalloproteinases, and, possibly, pore-forming proteins—and is only partially characterized. Scyphozoan stings may lead to local and systemic reactions via toxic and immunological mechanisms; some of these reactions may represent a medical emergency. However, the adoption of safe and efficacious first aid measures for jellyfish stings is hampered by the diffusion of folk remedies, anecdotal reports, and lack of consensus in the scientific literature. Species-specific differences may hinder the identification of treatments that work for all stings. However, rinsing the sting site with vinegar (5% acetic acid) and the application of heat (hot pack/immersion in hot water) or lidocaine appear to be substantiated by evidence. Controlled clinical trials or reliable models of envenomation are warranted to confirm the efficacy and safety of these approaches and identify possible species-specific exceptions. Knowledge of the precise composition of Scyphozoa venom may open the way to molecule-oriented therapies in the future.

The chemical armament of reef-building corals: inter- and intra-specific variation and the identification of an unusual actinoporin in Stylophora pistilata

Corals, like other cnidarians, are venomous animals that rely on stinging cells (nematocytes) and their toxins to catch prey and defend themselves against predators. However, little is known about the chemical arsenal employed by stony corals, despite their ecological importance. Here, we show large differences in the density of nematocysts and whole-body hemolytic activity between different species of reef-building corals. In the branched coral Stylophora pistillata, the tips of the branches exhibited a greater hemolytic activity than the bases. Hemolytic activity and nematocyst density were significantly lower in Stylophora that were maintained for close to a year in captivity compared to corals collected from the wild. A cysteine-containing actinoporin was identified in Stylophora following partial purification and tandem mass spectrometry. This toxin, named Δ-Pocilopotoxin-Spi1 (Δ-PCTX-Spi1) is the first hemolytic toxin to be partially isolated and characterized in true reef-building corals. Loss of hemolytic activity during chromatography suggests that this actinoporin is only one of potentially several hemolytic molecules. These results suggest that the capacity to employ offensive and defensive chemicals by corals is a dynamic trait within and between coral species, and provide a first step towards identifying the molecular components of the coral chemical armament.

Sea Anemones: Quiet Achievers in the Field of Peptide Toxins

Sea anemones have been understudied as a source of peptide and protein toxins, with relatively few examined as a source of new pharmacological tools or therapeutic leads. This is surprising given the success of some anemone peptides that have been tested, such as the potassium channel blocker from Stichodactyla helianthus known as ShK. An analogue of this peptide, ShK-186, which is now known as dalazatide, has successfully completed Phase 1 clinical trials and is about to enter Phase 2 trials for the treatment of autoimmune diseases. One of the impediments to the exploitation of sea anemone toxins in the pharmaceutical industry has been the difficulty associated with their high-throughput discovery and isolation. Recent developments in multiple ‘omic’ technologies, including genomics, transcriptomics and proteomics, coupled with advanced bioinformatics, have opened the way for large-scale discovery of novel sea anemone toxins from a range of species. Many of these toxins will be useful pharmacological tools and some will hopefully prove to be valuable therapeutic leads.