First Proteome of the Egg Perivitelline Fluid of a Freshwater Gastropod with Aerial Oviposition

Phylogenetic variations in a novel family of hyperstable apple snail egg proteins: insights into structural stability and functional trends

The relationship between protein stability and functional evolution is little explored in proteins purified from natural sources. Here, we investigated a novel family of egg proteins (Perivitellin-1, PV1) from Pomacea snails. Their remarkable stability and clade-related functions in most derived clades (Canaliculata and Bridgesii) make them excellent candidates for exploring this issue. To that aim, we studied PV1 (PpaPV1) from the most basal lineage, Flagellata. PpaPV1 displays unparalleled structural and kinetic stability, surpassing PV1s from derived clades, ranking among the most hyperstable proteins documented in nature. Its spectral features contribute to a pale egg coloration, exhibiting a milder glycan binding lectin activity with a narrower specificity than PV1s from the closely related Bridgesii clade. These findings provide evidence for substantial structural and functional changes throughout the genus' PV1 evolution. We observed that structural and kinetic stability decreased in a clade-related fashion and was associated with large variations in defensive traits. For instance, pale PpaPV1 lectin turns potent in the Bridgesii clade, adversely affecting gut morphology, while giving rise to brightly colored PV1s providing eggs with a conspicuous, probably warning signal in the Canaliculata clade. This work provides a comprehensive comparative analysis of PV1s from various apple snail species within a phylogenetic framework, offering insights into the interplay among their structural features, stability profiles and functional roles. More broadly, our work provides one of the first examples from natural evolution showing the crucial link among protein structure, stability and evolution of new functions.

Egg-associated secretions from the brown planthopper (Nilaparvata lugens) activate rice immune responses

The brown planthopper (BPH, Nilaparvata lugens) is a notorious sap-sucking insect pest that damages rice (Oryza sativa) plants throughout Asia. During BPH feeding, saliva enters rice plant tissues, whereas during oviposition egg-associated secretions (EAS) are deposited in damaged plant tissue. Dynamic changes in rice to planthopper salivary effectors have been widely reported. However, the effects of EAS from planthopper on rice immunity remains largely unexplored. In this study, we found that both infestation of rice by gravid BPH female adults and treatment with the EAS elicited a strong and rapid accumulation of jasmonic acid (JA), JA-isoleucine, and hydrogen peroxide in rice. EAS enhanced plant defenses not only in rice but also in tobacco, and these impaired the performance of BPH on rice, as well as the performance of aphids and whiteflies on tobacco. High-throughput proteome sequencing of EAS led to 110 proteins being identified and 53 proteins with 2 or more unique peptides being detected. Some proteins from BPH EAS were also found in the salivary proteome from herbivores, suggesting potential evolutionary conservation of effector functions across feeding and oviposition; however, others were only identified in EAS, and these are likely specifically related to oviposition. These findings point to novel proteins affecting interactions between planthoppers and rice during oviposition, providing an additional source of information for effector studies.

Proteomic analysis of digestive tract peptidases and lipases from the invasive gastropod Pomacea canaliculata

BACKGROUND

The invasive gastropod Pomacea canaliculata has received great attention in the last decades as a result of its negative impact on crops agriculture, yet knowledge of their digestive physiology remains incomplete, particularly the enzymatic breakdown of macromolecules such as proteins and lipids.

RESULTS

Discovery proteomics revealed aspartic peptidases, cysteine peptidases, serine peptidases, metallopeptidases and threonine peptidases, as well as acid and neutral lipases and phospholipases along the digestive tract of P. canaliculata. Peptides specific to peptidases (139) and lipases (14) were quantified by targeted mass spectrometry. Digestion begins in the mouth via diverse salivary peptidases (nine serine peptidases; seven cysteine peptidases, one aspartic peptidase and 22 metallopeptidases) and then continues in the oesophagus (crop) via three luminal metallopeptidases (Family M12) and six serine peptidases (Family S1). Downstream, the digestive gland provides a battery of enzymes composed of aspartic peptidase (one), cysteine peptidases (nine), serine peptidases (12) and metallopeptidases (24), including aminopeptidases, carboxypeptidases and dipeptidases). The coiled gut has M1 metallopeptidases that complete the digestion of small peptides. Lipid extracellular digestion is completed by triglyceride lipases.

CONCLUSION

From an integrative physiological and anatomical perspective, P. canaliculata shows an unexpected abundance and diversity of peptidases, which participate mainly in extracellular digestion. Moreover, the previously unknown occurrence of luminal lipases from the digestive gland is reported for the first time. Salivary and digestive glands were the main tissues involved in the synthesis and secretion of these enzymes, but plausibly the few luminally exclusive peptidases are secreted by ventrolateral pouches or epithelial unicellular glands. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Occurrence of microplastics in freshwater gastropods from a tropical river U-Taphao, southern Thailand

Background

Microplastics (MPs) are pollutants in rivers and marine environments. Rivers can be sources and sinks of MPs that enter the biota. Previous studies focusing on freshwater species are quite limited, especially for gastropods. Freshwater gastropods are essential to aquatic ecosystems because they are food to other aquatic animals, such as fish, shrimp, and crabs. They are a crucial link in the food chain between water resources and human food. Therefore, this study aimed to investigate MP accumulation in freshwater gastropods, commonly known as snails (Filopaludina sumatrensis speciosa and Pomacea canaliculata), in a river flowing into a shallow coastal lagoon.

Method

In this study, snail tissue samples were digested with 30% hydrogen peroxide. The mixture was heated at 60 °C for 24 h. MP particles were identified, counted, and characterized (shape, size, and color) by visual identification under a stereomicroscope. Furthermore, polymer-type identification was performed using Fourier transform infrared spectroscopy (FTIR). Analysis of variance (ANOVA) was applied for the statistical analysis.

Results

The MPs found were as follows: 4.76 particles/individual were found in F. sumatrensis speciosa upstream, 5.20 particles/individual were found in F. sumatrensis speciosa downstream, 7.28 particles/individual were found in P. canaliculata upstream, and 4.00 particles/individual were found in P. canaliculata downstream. It was found in the two-way ANOVA that the accumulation of MPs in gastropods was affected by species and study sites (upstream and downstream). There was a significant difference in the amount of MPs in P. canaliculata between upstream and downstream sites (p = 0.003). Fibers were the most common MPs in both species. Moreover, P. canaliculata upstream had the most significant amount of MPs. The smallest amount of MPs was recorded for P. canaliculata downstream, but there was great diversity in shape, size, and polymer type. MPs sized 500 μm^-1 mm were the most common in both species. Fourier transform infrared spectroscopy revealed six polymers: poly (ethylene terephthalate), polypropylene, rayon, polyethyleneimine, polyamine, and poly (propylene: ethylene). The occurrence of MPs in gastropods is alarming for food security in Thailand. The results of this study can be used to support baseline data on MP accumulation among freshwater gastropods.

Unveiling Putative Functions of Mucus Proteins and Their Tryptic Peptides in Seven Gastropod Species Using Comparative Proteomics and Machine Learning-Based Bioinformatics Predictions

Gastropods are among the most diverse animals. Gastropod mucus contains several glycoproteins and peptides that vary by species and habitat. Some bioactive peptides from gastropod mucus were identified only in a few species. Therefore, using biochemical, mass spectrometric, and bioinformatics approaches, this study aimed to comprehensively identify putative bioactive peptides from the mucus proteomes of seven commonly found or commercially valuable gastropods. The mucus was collected in triplicate samples, and the proteins were separated by 1D-SDS-PAGE before tryptic digestion and peptide identification by nano LC-MS/MS. The mucus peptides were subsequently compared with R scripts. A total of 2818 different peptides constituting 1634 proteins from the mucus samples were identified, and 1218 of these peptides (43%) were core peptides found in the mucus of all examined species. Clustering and correspondence analyses of 1600 variable peptides showed unique mucous peptide patterns for each species. The high-throughput k-nearest neighbor and random forest-based prediction programs were developed with more than 95% averaged accuracy and could identify 11 functional categories of putative bioactive peptides and 268 peptides (9.5%) with at least five to seven bioactive properties. Antihypertensive, drug-delivering, and antiparasitic peptides were predominant. These peptides provide an understanding of gastropod mucus, and the putative bioactive peptides are expected to be experimentally validated for further medical, pharmaceutical, and cosmetic applications.

Transcriptomic analysis and expression of C-type lectins in response to Vibrio parahaemolyticus challenge in Scapharca subcrenata

Little information is available on innate immune defense mechanisms of Scapharca subcrenata. C-type lectins (CTLs) are not only pattern recognition proteins that can bind pathogen-associated molecular patterns, but also crucial maternally-derived immune factors in mollusc egg. In this study, the comparative transcriptome analysis of Vibrio parahaemolyticus-infected and untreated hepatopancreas were performed to identify the key genes involved in maternal transfer of immunity. A total of 3514 and 9327 differentially expressed genes (DEGs) were identified at 6 and 48 h post challenge compared to control groups. Gene Ontology and Cluster of Orthologous Groups analysis showed that most DEGs were classified under regulation of signal transduction, regulation of the metabolic process of carbohydrates and secondary metabolites, while the processes of posttranscriptional modification and protein translation were inhibited manifestly. The DEGs were most enriched in pathways related to lysosome, phagosome and EMC-receptor interaction. Among the DEGs, 191 maternal immune-related genes that could provide developing embryos a better protection against pathogen infection were identified according to previous studies. Additionally, five CTLs (designated as SsCTL1-5) identified from the DEGs were cloned, and their expression patterns in different tissues and post immune stimulation were analyzed. These findings would be beneficial for understanding the innate immune defense mechanisms of S. subcrenata.

A highly stable, non-digestible lectin from Pomacea diffusa unveils clade-related protection systems in apple snail eggs

The acquisition of egg protection is vital for species survival. Poisonous eggs from Pomacea apple snails have defensive macromolecules for protection. Here we isolated and characterized a novel lectin called PdPV1 that is massively accumulated in the eggs of Pomacea diffusa and seems part of its protective cocktail. The native protein, an oligomer of ca 256 kDa, has high structural stability, withstanding 15 min boiling and denaturing by SDS. It resists in vitro proteinase digestion and displays structural stability between pH 2.0 and pH 12.0, and up to 85°C. These properties, as well as its subunit sequences, glycosylation pattern, presence of carotenoids, size and global shape resemble those of its orthologs from other Pomacea. Furthermore, like members of the canaliculata clade, PdPV1 is recovered unchanged in feces of mice ingesting it, supporting an anti-nutritive defensive function. PdPV1 also displays a strong hemagglutinating activity, specifically recognizing selected ganglioside motifs with high affinity. This activity is only shared with PsSC, a perivitelline from the same clade (bridgesii clade). As a whole, these results indicate that species in the genus Pomacea have diversified their egg defenses: those from the bridgesii clade are protected mostly by non-digestible lectins that lower the nutritional value of eggs, in contrast with protection by neurotoxins of other Pomacea clades, indicating that apple snail egg defensive strategies are clade specific. The harsh gastrointestinal environment of predators would have favored their appearance, extending by convergent evolution the presence of plant-like highly stable lectins, a strategy not reported in other animals.

The Zebrafish Perivitelline Fluid Provides Maternally-Inherited Defensive Immunity

In the teleost egg, the embryo is immersed in an extraembryonic fluid that fills the space between the embryo and the chorion and partially isolates it from the external environment, called the perivitelline fluid (PVF). The exact composition of the PVF remains unknown in vertebrate animals. The PVF allows the embryo to avoid dehydration, to maintain a safe osmotic balance and provides mechanical protection; however, its potential defensive properties against bacterial pathogens has not been reported. In this work, we determined the global proteomic profile of PVF in zebrafish eggs and embryos, and the maternal or zygotic origin of the identified proteins was studied. In silico analysis of PVF protein composition revealed an enrichment of protein classes associated with non-specific humoral innate immunity. We found lectins, protease inhibitors, transferrin, and glucosidases present from early embryogenesis until hatching. Finally, in vitro and in vivo experiments done with this fluid demonstrated that the PVF possessed a strong agglutinating capacity on bacterial cells and protected the embryos when challenged with the pathogenic bacteria Edwardsiella tarda. Our results suggest that the PVF is a primitive inherited immune extraembryonic system that protects the embryos from external biological threats prior to hatching.

Pectenovarin, A New Ovarian Carotenoprotein from Japanese Scallop Mizuhopecten yessoensis

The scallop Mizuhopecten yessoensis accumulates carotenoids in the ovary during the maturation stage. Its conspicuous pink color implies the presence of carotenoprotein. However, the carotenoprotein from the scallop ovary has never been isolated and characterized, probably due to its instability and complexity. Here, we developed an extraction and isolation procedure for the carotenoprotein by employing a basic buffer containing potassium bromide to facilitate its efficient extraction from the ovary, and we succeeded in obtaining the carotenoprotein, termed pectenovarin. The carotenoid composition of the pectenovarin was similar to that of the ovary. The N-terminal and internal amino acid sequences of pectenovarin showed a high similarity to those of vitellogenin, the precursor of egg yolk protein under analysis.

Multi-omics investigations within the Phylum Mollusca, Class Gastropoda: from ecological application to breakthrough phylogenomic studies

Gastropods are the largest and most diverse class of mollusc and include species that are well studied within the areas of taxonomy, aquaculture, biomineralization, ecology, microbiome and health. Gastropod research has been expanding since the mid-2000s, largely due to large-scale data integration from next-generation sequencing and mass spectrometry in which transcripts, proteins and metabolites can be readily explored systematically. Correspondingly, the huge data added a great deal of complexity for data organization, visualization and interpretation. Here, we reviewed the recent advances involving gastropod omics ('gastropodomics') research from hundreds of publications and online genomics databases. By summarizing the current publicly available data, we present an insight for the design of useful data integrating tools and strategies for comparative omics studies in the future. Additionally, we discuss the future of omics applications in aquaculture, natural pharmaceutical biodiscovery and pest management, as well as to monitor the impact of environmental stressors.

Egg perivitelline fluid proteome of a freshwater snail: Insight into the transition from aquatic to terrestrial egg deposition

RATIONALE

Proteins from the egg perivitelline fluid (PVF) are assumed to play critical roles in embryonic development, but for many groups of animals their identities remain unknown. Identifying egg PVF proteins is a critical step towards understanding their functions including their roles in evolutionary transition in habitats.

METHODS

We applied proteomic and transcriptomic analysis to investigate the PVF proteome of the eggs of Pomacea diffusa, an aerial ovipositing freshwater snail in the family Ampullariidae. The PVF proteins were separated with the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) method, and proteomic analysis was conducted using an LTQ Velos ion trap mass spectrometer coupled with liquid chromatography. Comparison of PVF proteomes and evolution analyses was performed between P. diffusa and other ampullariids.

RESULTS

In total, 32 egg PVF proteins were identified from P. diffusa. They were categorized as PV1-like subunits, immune-responsive proteins, protein degradation, signaling and binding, transcription and translation, metabolism, oxidation-reduction and proteins with unknown function. Interestingly, the proteome includes a calcium-binding protein important in forming the hard eggshell that enabled the terrestrial transition. However, it does not include PV2, a neurotoxic protein that was assumed to be present in all Pomacea species.

CONCLUSIONS

The PVF proteome data from P. diffusa can help us better understand the roles that reproductive proteins played during the transition from underwater to terrestrial egg deposition. Moreover, they could be useful in comparative studies of the terrestrialization in several groups of animals that occurred independently during their evolution.

Novel Role for Animal Innate Immune Molecules: Enterotoxic Activity of a Snail Egg MACPF-Toxin

Gastropod Molluscs rely exclusively on the innate immune system to protect from pathogens, defending their embryos through maternally transferred effectors. In this regard, Pomacea snail eggs, in addition to immune defenses, have evolved the perivitellin-2 or PV2 combining two immune proteins into a neurotoxin: a lectin and a pore-forming protein from the Membrane Attack Complex/Perforin (MACPF) family. This binary structure resembles AB-toxins, a group of toxins otherwise restricted to bacteria and plants. Many of these are enterotoxins, leading us to explore this activity in PV2. Enterotoxins found in bacteria and plants act mainly as pore-forming toxins and toxic lectins, respectively. In animals, although both pore-forming proteins and lectins are ubiquitous, no enterotoxins have been reported. Considering that Pomacea snail eggs ingestion induce morpho-physiological changes in the intestinal mucosa of rodents and is cytotoxic to intestinal cells in culture, we seek for the factor causing these effects and identified PmPV2 from Pomacea maculata eggs. We characterized the enterotoxic activity of PmPV2 through in vitro and in vivo assays. We determined that it withstands the gastrointestinal environment and resisted a wide pH range and enzymatic proteolysis. After binding to Caco-2 cells it promoted changes in surface morphology and an increase in membrane roughness. It was also cytotoxic to both epithelial and immune cells from the digestive system of mammals. It induced enterocyte death by a lytic mechanism and disrupted enterocyte monolayers in a dose-dependent manner. Further, after oral administration to mice PmPV2 attached to enterocytes and induced large dose-dependent morphological changes on their small intestine mucosa, reducing the absorptive surface. Additionally, PmPV2 was detected in the Peyer's patches where it activated lymphoid follicles and triggered apoptosis. We also provide evidence that the toxin can traverse the intestinal barrier and induce oral adaptive immunity with evidence of circulating antibody response. As a whole, these results indicate that PmPV2 is a true enterotoxin, a role that has never been reported to lectins or perforin in animals. This extends by convergent evolution the presence of plant- and bacteria-like enterotoxins to animals, thus expanding the diversity of functions of MACPF proteins in nature.

Signatures of Divergence, Invasiveness, and Terrestrialization Revealed by Four Apple Snail Genomes

The family Ampullariidae includes both aquatic and amphibious apple snails. They are an emerging model for evolutionary studies due to the high diversity, ancient history, and wide geographical distribution. Insight into drivers of ampullariid evolution is hampered, however, by the lack of genomic resources. Here, we report the genomes of four ampullariids spanning the Old World (Lanistes nyassanus) and New World (Pomacea canaliculata, P. maculata, and Marisa cornuarietis) clades. The ampullariid genomes have conserved ancient bilaterial karyotype features and a novel Hox gene cluster rearrangement, making them valuable in comparative genomic studies. They have expanded gene families related to environmental sensing and cellulose digestion, which may have facilitated some ampullarids to become notorious invasive pests. In the amphibious Pomacea, novel acquisition of an egg neurotoxin and a protein for making the calcareous eggshell may have been key adaptations enabling their transition from underwater to terrestrial egg deposition.

Comparative Proteomics on Deep-Sea Amphipods after in Situ Copper Exposure

The interest in deep-sea mining increased along with the environmental concerns of these activities to the deep-sea fauna. The discovery of optimal biomarkers of deep-sea mining activities in deep-sea species is a crucial step toward the supply of important ecological information for environmental impact assessment. In this study, an in situ copper exposure experiment was performed on deep-sea scavenging amphipods. Abyssorchomene distinctus individuals were selected among all the exposed amphipods for molecular characterization. Copper concentration within the gut was assessed, followed by a tandem mass tag-based coupled with two-dimensional liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) applied to identify and quantify the protein expression changes after 48 h of exposure. 2937 proteins were identified and annotated, and 1918 proteins among all identified proteins were assigned by at least two nonambiguous peptides. The screening process was performed based on the differences in protein abundance and the specific correlation between the proteins and copper in previous studies. These differentially produced proteins include Na⁺/K⁺ ATPase, cuticle, chitinase, and proteins with unknown function. Their abundances showed correlation with copper and had high sensitivity to indicate the copper level, being here proposed as biomarker candidates for deep-sea mining activities in the future. This is a key step in the development of environmental impact assessment of deep-sea mining activities integrating ecotoxicological data.

Non-digestible proteins and protease inhibitors: implications for defense of the colored eggs of the freshwater apple snailPomacea canaliculata

Apple snails (Pomacea Perry, 1810) are successful invaders that cause ecological perturbations, economic losses, and medical issues. A peculiar trait of this snail is a high biological potential, related to the absence of predators of their eggs. Eggs show protease inhibitor (PI) activity, originally ascribed to PcOvo perivitellin in the apple snail Pomacea canaliculata (Lamarck, 1822) but absent in PmPV1, the orthologoue of PcOvo, in eggs of the apple snail Pomacea maculata Perry, 1810. As egg fluid diminishes rat growth rate, an antidigestive effect, similar to plant defenses against herbivory, was hypothesized. However, PI activity has not been characterized in apple snail eggs. Here we identify and partially characterize P. canaliculata egg PI and improve our knowledge of the quaternary structure and evolution of PcOvo. Through N-terminal, transcriptomic or proteomic sequencing, and biochemical validation, we identified a Kunitz-type and a Kazal-type inhibitor that, though at low concentration in the egg, exhibit strong PI activity against trypsin, chymotrypsin, elastase, and subtilisin. Additionally, we report three new subunits for the non-digestible storage protein PcOvo. They are likely products of ancient gene duplication, as their sequences exhibit moderate similarity (30%). To our knowledge, this is the first report of Kazal-type inhibition among invertebrate eggs. Inhibiting varied proteases, PI seems an efficient adaptive trait that limits predator’s capacity to digest egg nutrients.

Understanding the transition from water to land: Insights from multi-omic analyses of the perivitelline fluid of apple snail eggs

Unlike most of the freshwater gastropod families, the family Ampullariidae includes members that exhibit both underwater and aerial oviposition, making it an ideal model for understanding mechanisms underlying the evolutionary transition from water to land. We applied SDS-PAGE and LC-MS/MS to analyse the proteome of the egg perivitelline fluid (PVF) of Marisa cornuarietis - an aquatic ovipositing ampullariid. Comparison with the reported PVF proteomes of two aerial ovipositing ampullariids (Pomacea canaliculata and P. maculata) showed that the three species all contain several major perivitellins that nourish the embryos. However, M. cornuarietis invests more heavily on immune-related proteins, which might be due to exposure to aquatic pathogens. Interestingly, only the PVF of out-of-water egg laying species have PV2 - a neurotoxin lethal to mice, and a calcium-binding protein which might be involved in the formation of calcareous eggshell. Integrated phylogenetic, evolutionary and gene expressional analyses detected the involvement of gene duplication, positive selection and neofunctionalisation in the formation of several major PVF proteins. Overall, our study provides multiple lines of evidence of adaptive evolution in the PVF proteins, and contributes to a better understanding of how aquatic gastropod ancestors invaded terrestrial habitats. SIGNIFICANCE: Aerial egg deposition has evolved in several groups of animals, but except for Vertebrata little is known about the mechanisms underlying this critical evolution process. We compared aquatic and aerial egg laying apple snails to understand the molecular mechanisms enabling such a transition in egg laying habitat. We found that the composition of perivitelline fluid proteomes of underwater and aerial egg depositors was remarkably different, and then gene duplication and positive selection were responsible for the formation of such novel proteins than enabled the evolutionary transition.

The genome of the golden apple snail Pomacea canaliculata provides insight into stress tolerance and invasive adaptation

Background

The golden apple snail (Pomacea canaliculata) is a freshwater snail listed among the top 100 worst invasive species worldwide and a noted agricultural and quarantine pest that causes great economic losses. It is characterized by fast growth, strong stress tolerance, a high reproduction rate, and adaptation to a broad range of environments.

Results

Here, we used long-read sequencing to produce a 440-Mb high-quality, chromosome-level assembly of the P. canaliculata genome. In total, 50 Mb (11.4%) repeat sequences and 21,533 gene models were identified in the genome. The major findings of this study include the recent explosion of DNA/hAT-Charlie transposable elements, the expansion of the P450 gene family, and the constitution of the cellular homeostasis system, which contributes to ecological plasticity in stress adaptation. In addition, the high transcriptional levels of perivitelline genes in the ovary and albumen gland promote the function of nutrient supply and defense ability in eggs. Furthermore, the gut metagenome also contains diverse genes for food digestion and xenobiotic degradation.

Conclusions

These findings collectively provide novel insights into the molecular mechanisms of the ecological plasticity and high invasiveness.

Biosynthesis in the Albumen Gland-Capsule Gland Complex Limits Reproductive Effort in the Invasive Apple Snail Pomacea canaliculata

High fecundity often contributes to successful invasives. In molluscs, this may be facilitated by the albumen gland-capsule gland complex, which in gastropods secretes the egg perivitelline fluid that nourishes and protects embryos. The biochemistry of the albumen gland-capsule gland complex and its relationship with fecundity remain largely unknown. We addressed these issues in Pomacea canaliculata (Lamarck, 1822), a highly invasive gastropod whose fecundity and reproductive effort exceed those of ecologically similar gastropods. We evaluated the dynamics of its major secretion compounds (calcium, polysaccharides, and total proteins) as well as the gene expression and stored levels of perivitellins during key moments of the reproductive cycle, that is, before and after first copulation and at low, medium, and high reproductive output. Copulation and first oviposition do not trigger the onset of albumen gland-capsule gland complex biosynthesis. On the contrary, soon after an intermediate reproductive effort, genes encoding perivitellins overexpressed. A high reproductive effort caused a decrease in all albumen gland-capsule gland complex secretion components. Right after a high reproductive output, the albumen gland-capsule gland complex restored the main secretion components, and calcium recovered baseline reserves; but proteins and polysaccharides did not. These metabolic changes in the albumen gland-capsule gland complex after multiple ovipositions were reflected in a reduction in egg mass but did not compromise egg quality. At the end of the cycle, egg dry weight almost doubled the initial albumen gland-capsule gland complex weight. Results indicate that albumen gland-capsule gland complex biosynthesis limits a constantly high reproductive output. Therefore, lowering fecundity by targeting biosynthesis could effectively reduce the rate of this species' spread.

A lectin of a non-invasive apple snail as an egg defense against predation alters the rat gut morphophysiology

The eggs of the freshwater Pomacea apple snails develop above the water level, exposed to varied physical and biological stressors. Their high hatching success seems to be linked to their proteins or perivitellins, which surround the developing embryo providing nutrients, sunscreens and varied defenses. The defensive mechanism has been unveiled in P. canaliculata and P. maculata eggs, where their major perivitellins are pigmented, non-digestible and provide a warning coloration while another perivitellin acts as a toxin. In P. scalaris, a species sympatric to the former, the defense strategy seems different, since no toxin was found and the major perivitellin, PsSC, while also colored and non-digestible, is a carbohydrate-binding protein. In this study we examine the structure and function of PsSC by sequencing its subunits, characterizing its carbohydrate binding profile and evaluating its effect on gut cells. Whereas cDNA sequencing and database search showed no lectin domain, glycan array carbohydrate binding profile revealed a strong specificity for glycosphingolipids and ABO group antigens. Moreover, PsSC agglutinated bacteria in a dose-dependent manner. Inspired on the defensive properties of seed lectins we evaluated the effects of PsSC on intestinal cells both in vitro (Caco-2 and IEC-6 cells) and in the gastrointestinal tract of rats. PsSC binds to Caco-2 cell membranes without reducing its viability, while a PsSC-containing diet temporarily induces large epithelium alterations and an increased absorptive surface. Based on these results, we propose that PsSC is involved in embryo defenses by altering the gut morphophysiology of potential predators, a convergent role to plant defensive lectins.

AmpuBase: a transcriptome database for eight species of apple snails (Gastropoda: Ampullariidae)

BACKGROUND

Gastropoda, with approximately 80,000 living species, is the largest class of Mollusca. Among gastropods, apple snails (family Ampullariidae) are globally distributed in tropical and subtropical freshwater ecosystems and many species are ecologically and economically important. Ampullariids exhibit various morphological and physiological adaptations to their respective habitats, which make them ideal candidates for studying adaptation, population divergence, speciation, and larger-scale patterns of diversity, including the biogeography of native and invasive populations. The limited availability of genomic data, however, hinders in-depth ecological and evolutionary studies of these non-model organisms.

RESULTS

Using Illumina Hiseq platforms, we sequenced 1220 million reads for seven species of apple snails. Together with the previously published RNA-Seq data of two apple snails, we conducted de novo transcriptome assembly of eight species that belong to five genera of Ampullariidae, two of which represent Old World lineages and the other three New World lineages. There were 20,730 to 35,828 unigenes with predicted open reading frames for the eight species, with N50 (shortest sequence length at 50% of the unigenes) ranging from 1320 to 1803 bp. 69.7% to 80.2% of these unigenes were functionally annotated by searching against NCBI's non-redundant, Gene Ontology database and the Kyoto Encyclopaedia of Genes and Genomes. With these data we developed AmpuBase, a relational database that features online BLAST functionality for DNA/protein sequences, keyword searching for unigenes/functional terms, and download functions for sequences and whole transcriptomes.

CONCLUSIONS

In summary, we have generated comprehensive transcriptome data for multiple ampullariid genera and species, and created a publicly accessible database with a user-friendly interface to facilitate future basic and applied studies on ampullariids, and comparative molecular studies with other invertebrates.

Convergent evolution of plant and animal embryo defences by hyperstable non-digestible storage proteins

Plants have evolved sophisticated embryo defences by kinetically-stable non-digestible storage proteins that lower the nutritional value of seeds, a strategy that have not been reported in animals. To further understand antinutritive defences in animals, we analysed PmPV1, massively accumulated in the eggs of the gastropod Pomacea maculata, focusing on how its structure and structural stability features affected its capacity to withstand passage through predator guts. The native protein withstands >50 min boiling and resists the denaturing detergent sodium dodecyl sulphate (SDS), indicating an unusually high structural stability (i.e., kinetic stability). PmPV1 is highly resistant to in vitro proteinase digestion and displays structural stability between pH 2.0-12.0 and 25-85 °C. Furthermore, PmPV1 withstands in vitro and mice digestion and is recovered unchanged in faeces, supporting an antinutritive defensive function. Subunit sequence similarities suggest a common origin and tolerance to mutations. This is the first known animal genus that, like plant seeds, lowers the nutritional value of eggs by kinetically-stable non-digestible storage proteins that survive the gut of predators unaffected. The selective pressure of the harsh gastrointestinal environment would have favoured their appearance, extending by convergent evolution the presence of plant-like hyperstable antinutritive proteins to unattended reproductive stages in animals.

Dataset for the proteomic and transcriptomic analyses of perivitelline fluid proteins in Pomacea snail eggs

This article describes how the proteomic and transcriptomic data were produced during a study of the reproductive proteins of Pomacea maculata, an aquatic apple snail laying colorful aerial eggs, and provides public access to the data. The data are related to a research article titled ‘An integrated proteomic and transcriptomic analysis of perivitelline fluid proteins in a freshwater gastropod laying aerial eggs’ (Mu et al., 2017) [1]. RNA was extracted from the albumen gland and other tissues and sequenced on an Illumina Hiseq. 2000. The assembled transcriptome was translated into protein sequences and then used for protein identification. Proteins from the perivitelline fluid of P. maculata were separated in SDS-PAGE and analyzed by LTQ-Orbitrap Elite coupled to an Easy-nLC. The translated transcriptome data are provided in this article. Proteomic data (.raw file format) are available via ProteomeXchange with the identifier PXD006718.

Apple Snail Perivitellin Precursor Properties Help Explain Predators' Feeding Behavior

In contrast with vitellogenin maturation, it is unknown whether gastropod perivitellin precursors are subject to large structural changes. The gastropod reproductive tract includes an accessory organ, the albumen gland (AG), that produces and secretes perivitelline fluid. In the apple snail Pomacea canaliculata, the large, reddish-pink AG provides eggs with perivitellins that are defensive against predators. Although the AG makes a considerable contribution to apple snail biomass, field observations indicate that it is rejected by avian and mammalian predators, although the underlying reason remains unknown. By analyzing the structure-function properties of P. canaliculata perivitellin precursors, we provide insight into perivitellin maturation and its relationship with apple snail predator feeding behavior. Structural analysis using small-angle X-ray scattering, absorption and fluorescence spectroscopy, circular dichroism, electrophoresis, chromatography, and partial proteolysis showed that the size, shape, and structure of perivitellin precursors resemble those of egg mature forms. Functional analysis indicates that the precursors of the defensive perivitellins ovorubin (PcOvo) and perivitellin-2 (PcPV2) are highly stable and antinutritive, withstanding proteinase digestion and displaying structural stability of their quaternary structure under a wide pH range (4.0-10.0). Furthermore, AG extracts limit a predator's ability to digest nutrients and are toxic to mice (median lethal concentration 96 h after administration: 5.9 mg/kg). Treated mice displayed neurologic signs similar to those produced by egg PcPV2. Results indicate that apple snails store active precursors of egg proteins inside the AG, providing evidence that gastropod perivitellin precursors do not experience the large structural processing of invertebrate vitellogenin maturation. These defensive proteins provide the apple snail AG with neurotoxic, antinutritive, and antidigestive activity, a likely explanation for the predators' feeding behavior.

Adaptation to deep-sea chemosynthetic environments as revealed by mussel genomes

Hydrothermal vents and methane seeps are extreme deep-sea ecosystems that support dense populations of specialized macro-benthos such as mussels. But the lack of genome information hinders the understanding of the adaptation of these animals to such inhospitable environments. Here we report the genomes of a deep-sea vent/seep mussel (Bathymodiolus platifrons) and a shallow-water mussel (Modiolus philippinarum). Phylogenetic analysis shows that these mussel species diverged approximately 110.4 million years ago. Many gene families, especially those for stabilizing protein structures and removing toxic substances from cells, are highly expanded in B. platifrons, indicating adaptation to extreme environmental conditions. The innate immune system of B. platifrons is considerably more complex than that of other lophotrochozoan species, including M. philippinarum, with substantial expansion and high expression levels of gene families that are related to immune recognition, endocytosis and caspase-mediated apoptosis in the gill, revealing presumed genetic adaptation of the deep-sea mussel to the presence of its chemoautotrophic endosymbionts. A follow-up metaproteomic analysis of the gill of B. platifrons shows methanotrophy, assimilatory sulfate reduction and ammonia metabolic pathways in the symbionts, providing energy and nutrients, which allow the host to thrive. Our study of the genomic composition allowing symbiosis in extremophile molluscs gives wider insights into the mechanisms of symbiosis in other organisms such as deep-sea tubeworms and giant clams.

An integrated proteomic and transcriptomic analysis of perivitelline fluid proteins in a freshwater gastropod laying aerial eggs

Proteins of the egg perivitelline fluid (PVF) that surrounds the embryo are critical for embryonic development in many animals, but little is known about their identities. Using an integrated proteomic and transcriptomic approach, we identified 64 proteins from the PVF of Pomacea maculata, a freshwater snail adopting aerial oviposition. Proteins were classified into eight functional groups: major multifunctional perivitellin subunits, immune response, energy metabolism, protein degradation, oxidation-reduction, signaling and binding, transcription and translation, and others. Comparison of gene expression levels between tissues showed that 22 PVF genes were exclusively expressed in albumen gland, the female organ that secretes PVF. Base substitution analysis of PVF and housekeeping genes between P. maculata and its closely related species Pomacea canaliculata showed that the reproductive proteins had a higher mean evolutionary rate. Predicted 3D structures of selected PVF proteins showed that some nonsynonymous substitutions are located at or near the binding regions that may affect protein function. The proteome and sequence divergence analysis revealed a substantial amount of maternal investment in embryonic nutrition and defense, and higher adaptive selective pressure on PVF protein-coding genes when compared with housekeeping genes, providing insight into the adaptations associated with the unusual reproductive strategy in these mollusks.

SIGNIFICANCE

There has been great interest in studying reproduction-related proteins as such studies may not only answer fundamental questions about speciation and evolution, but also solve practical problems of animal infertility and pest outbreak. Our study has demonstrated the effectiveness of an integrated proteomic and transcriptomic approach in understanding the heavy maternal investment of proteins in the eggs of a non-model snail, and how the reproductive proteins may have evolved during the transition from laying underwater eggs to aerial eggs.

Effects of dietary supplementation of golden apple snail (Pomacea canaliculata) egg on survival, pigmentation and antioxidant activity of Blood parrot

This study aims to evaluate the effects of supplementing golden apple snail (Pomacea canaliculata) eggs powder (EP) in the diet as a source of natural carotenoids on survival, pigmentation and antioxidant activity of Blood parrot. A total of 90 fish were divided into three treatment groups with three replicates per treatment. Blood parrot were fed with diets containing 0 (control), 5 % (EP 5 %), and 15 % (EP 15 %) dry powder of golden apple snail egg for 60 days, and nine fish per group were sampled at 20, 40, and 60 days. No differences in survival of the fish among treatments were found throughout the experiment. The body coloration of Blood parrot was enhanced in the skin and caudal fin with increasing content of golden apple snail egg powder in the diet. At the end of the experiment, the carotenoid content in the caudal fin and the number of scale chromatophores of the fish fed dietary with EP were higher (P < 0.05) than those of the control group. The EP 15 % treated fishes showed a significant higher (P < 0.05) in the activities of SOD after 60 days, but we could not observe significant changes (P > 0.05) in CAT activities. Results demonstrated that golden apple snail eggs can be used as a colorant to promote the pigmentation efficacy of Blood parrot.

The eggs of the apple snail Pomacea maculata are defended by indigestible polysaccharides and toxic proteins

The freshwater snails Pomacea Perry, 1810 lay conspicuous aerial egg clutches that are ignored by most predators. Egg biochemical defenses in the apple snail Pomacea canaliculata (Lamarck, 1822) are provided by multifunctional proteins. We analyzed the eggs of a sympatric species, Pomacea maculata Perry, 1810, studying the gross composition, toxicity, hemagglutinating activity, and its antinutritive and antidigestive properties. Eggs are mostly composed of polysaccharides (mainly galactogen) and proteins, followed by lipids and nonsoluble calcium. Two perivitellins account for ∼85% dry mass of the egg protein. The major lipids are phospholipids and sterols. A suite of potential defenses was determined, including strong lethal neurotoxicity on mice and moderate antidigestive and lectin activities. Remarkably, their polysaccharides were refractive to in vitro digestion by digestive glycosidases. This study characterized ∼99% of egg composition and identified multiple potential defenses, provided not only by proteins but also by polysaccharides. This is the first evidence to our knowledge that reserve sugars may be involved in defenses, giving further insight into the unusual reproductive strategy of these well-defended snail eggs.

Transcriptomic and Proteomic Analysis of Arion vulgaris--Proteins for Probably Successful Survival Strategies?

The Spanish slug, Arion vulgaris, is considered one of the hundred most invasive species in Central Europe. The immense and very successful adaptation and spreading of A. vulgaris suggest that it developed highly effective mechanisms to deal with infections and natural predators. Current transcriptomic and proteomic studies on gastropods have been restricted mainly to marine and freshwater gastropods. No transcriptomic or proteomic study on A. vulgaris has been carried out so far, and in the current study, the first transcriptomic database from adult specimen of A. vulgaris is reported. To facilitate and enable proteomics in this non-model organism, a mRNA-derived protein database was constructed for protein identification. A gel-based proteomic approach was used to obtain the first generation of a comprehensive slug mantle proteome. A total of 2128 proteins were unambiguously identified; 48 proteins represent novel proteins with no significant homology in NCBI non-redundant database. Combined transcriptomic and proteomic analysis revealed an extensive repertoire of novel proteins with a role in innate immunity including many associated pattern recognition, effector proteins and cytokine-like proteins. The number and diversity in gene families encoding lectins point to a complex defense system, probably as a result of adaptation to a pathogen-rich environment. These results are providing a fundamental and important resource for subsequent studies on molluscs as well as for putative antimicrobial compounds for drug discovery and biomedical applications.

Integration of Transcriptomic and Proteomic Approaches Provides a Core Set of Genes for Understanding of Scallop Attachment

Attachment is an essential physiological process in life histories of many marine organisms. Using a combination of transcriptomic and proteomic approach, scallop byssal proteins (Sbps) and their associated regulatory network genes were investigated for the first time. We built the first scallop foot transcriptome library, and 75 foot-specific genes were identified. Through integration of transcriptomic-proteomic approach, seven unique Sbps were identified. Of them, three showed significant amino acid sequence homology to known proteins. In contrast, the rest did not show significant protein matches, indicating they are possibly novel proteins. Our transcriptomic and proteomic analyses also suggest that post-translational modification may be one of the significant features for Sbps as well. Taken together, our study provides the first multidimensional collection of a core set of genes that may be potentially involved in scallop byssal attachment.

Extraction and identification of membrane proteins from black widow spider eggs

The eggs of oviparous animals are storehouses of maternal proteins required for embryonic development. Identification and molecular characterization of such proteins will provide much insight into the regulation of embryonic development. We previously analyzed soluble proteins in the eggs of the black widow spider (Latrodectus tredecimguttatus), and report here on the extraction and mass spectrometric identification of the egg membrane proteins. Comparison of different lysis solutions indicated that the highest extraction of the membrane proteins was achieved with 3%-4% sodium laurate in 40 mmol/L Tris-HCl buffer containing 4% CHAPS and 2% DTT (pH 7.4). SDS-PAGE combined with nLC-MS/MS identified 39 proteins with membrane-localization annotation, including those with structural, catalytic, and regulatory activities. Nearly half of the identified membrane proteins were metabolic enzymes involved in various cellular processes, particularly energy metabolism and biosynthesis, suggesting that relevant metabolic processes were active during the embryonic development of the eggs. Several identified cell membrane proteins were involved in the special structure formation and function of the egg cell membranes. The present proteomic analysis of the egg membrane proteins provides new insight into the molecular mechanisms of spider embryonic development.

Sperm proteome of Mytilus galloprovincialis: Insights into the evolution of fertilization proteins in marine mussels

Cataloging the sperm proteome of an animal can improve our understanding of its sperm-egg interaction and speciation, but such data are available for only a few free-spawning invertebrates. This study aimed to identify the sperm proteome of Mytilus galloprovincialis, a free-spawning marine mussel. We integrated public transcriptome datasets by de novo assembly, and applied SDS-PAGE coupled LC-MS/MS analysis to profile the sperm proteome, resulting in the identification of 550 proteins. Comparing the homologous sperm protein coding genes between M. galloprovincialis and its closely related species M. edulis revealed that fertilization proteins have the highest mean nonsynonymous substitution rate (Ka/Ks = 0.62) among 11 functional groups, consistent with previous reports of positive selection of several fertilization proteins in Mytilus. Moreover, 78 sperm proteins in different functional groups have Ka/Ks values > 0.5, indicating the presence of many candidate sperm proteins for further analysis of rapid interspecific divergence. The MS data are available in ProteomeXchange with the identifier PXD001665.

Maternal immune transfer in mollusc

Maternal immunity refers to the immunity transferred from mother to offspring via egg, playing an important role in protecting the offspring at early life stages and contributing a trans-generational effect on offspring's phenotype. Because fertilization is external in most of the molluscs, oocytes and early embryos are directly exposed to pathogens in the seawater, and thus maternal immunity could provide a better protection before full maturation of their immunological systems. Several innate immune factors including pattern recognition receptors (PRRs) like lectins, and immune effectors like lysozyme, lipopolysaccharide binding protein/bacterial permeability-increasing proteins (LBP/BPI) and antioxidant enzymes have been identified as maternally derived immune factors in mollusc eggs. Among these immune factors, some maternally derived lectins and antibacterial factors have been proved to endue mollusc eggs with effective defense ability against pathogen infection, while the roles of other factors still remain untested. The physiological condition of mollusc broodstock has a profound effect on their offspring fitness. Many other factors such as nutrients, pathogens, environment conditions and pollutants could exert considerable influence on the maternal transfer of immunity. The parent molluscs which have encountered an immune stimulation endow their offspring with a trans-generational immune capability to protect them against infections effectively. The knowledge on maternal transfer of immunity and the trans-generational immune effect could provide us with an ideal management strategy of mollusc broodstock to improve the immunity of offspring and to establish a disease-resistant family for a long-term improvement of cultured stocks.

Proteomic profiling during the pre-competent to competent transition of the biofouling polychaete Hydroides elegans

The polychaete, Hydroides elegans, is a tube-building worm that is widely distributed in tropical and subtropical seas. It is a dominant fouling species and thus a major target organism in antifouling research. Here, the first high-throughput proteomic profiling of pre-competent and competent larvae of H. elegans is reported with the identification of 1,519 and 1,322 proteins, respectively. These proteins were associated with a variety of biological processes. However, a large proportion was involved in energy metabolism, redox homeostasis, and microtubule-based processes. A comparative analysis revealed 21 proteins that were differentially regulated in larvae approaching competency.

Insights into embryo defenses of the invasive apple snail Pomacea canaliculata: egg mass ingestion affects rat intestine morphology and growth

Background

The spread of the invasive snail Pomacea canaliculata is expanding the rat lungworm disease beyond its native range. Their toxic eggs have virtually no predators and unusual defenses including a neurotoxic lectin and a proteinase inhibitor, presumably advertised by a warning coloration. We explored the effect of egg perivitellin fluid (PVF) ingestion on the rat small intestine morphology and physiology.

Methodology/Principal Findings

Through a combination of biochemical, histochemical, histopathological, scanning electron microscopy, cell culture and feeding experiments, we analyzed intestinal morphology, growth rate, hemaglutinating activity, cytotoxicity and cell proliferation after oral administration of PVF to rats. PVF adversely affects small intestine metabolism and morphology and consequently the standard growth rate, presumably by lectin-like proteins, as suggested by PVF hemaglutinating activity and its cytotoxic effect on Caco-2 cell culture. Short-term effects of ingested PVF were studied in growing rats. PVF-supplemented diet induced the appearance of shorter and wider villi as well as fused villi. This was associated with changes in glycoconjugate expression, increased cell proliferation at crypt base, and hypertrophic mucosal growth. This resulted in a decreased absorptive surface after 3 days of treatment and a diminished rat growth rate that reverted to normal after the fourth day of treatment. Longer exposure to PVF induced a time-dependent lengthening of the small intestine while switching to a control diet restored intestine length and morphology after 4 days.

Conclusions/Significance

Ingestion of PVF rapidly limits the ability of potential predators to absorb nutrients by inducing large, reversible changes in intestinal morphology and growth rate. The occurrence of toxins that affect intestinal morphology and absorption is a strategy against predation not recognized among animals before. Remarkably, this defense is rather similar to the toxic effect of plant antipredator strategies. This defense mechanism may explain the near absence of predators of apple snail eggs.

Filled with nutritious substances to nourish the embryos, eggs of most animals are often the targets of pathogens and predators. An exception are the eggs of Pomacea canaliculata –known as the apple snail– which have hardly any predators. This freshwater snail is a serious aquatic crop pest in several continents, listed among the 100 worst invasive species. It is the host of a roundworm responsible for the rat lungworm disease causing human eosinophilic meningitis. The spread of this emerging infectious disease has been associated with the expansion of apple snails. They lay eggs above water level in bright pink-reddish masses, presumably a warning coloration. Indeed, eggs have chemical defenses, including neurotoxic and antinutritive proteins. The authors found that the ingestion of egg extracts adversely affects rat small intestine inducing large, reversible changes in the intestinal wall that limits the ability to absorb egg nutrients causing a diminished growth rate. Apple snail eggs are the first animal known to deter predators by this mechanism, but remarkably this defense is rather similar to the toxic effect of plant seeds proteins. These overlapping egg defenses that predators have not managed to overcome yet may partially explain the reproductive success of P. canaliculata.

iTRAQ-based quantitative proteomic analysis reveals acute hypo-osmotic responsive proteins in the gills of the Japanese eel (Anguilla japonica)

Osmoregulation in fish has been a classical research topic for several decades. Salmon and eels are the widely used model animals because of their wide distribution in different geographical locations and spawning migration between fresh- and salt-water habitats. Numerous fish osmoregulatory hormones and ion transporters were identified for their essential roles in acclimation and adaptation to waters of different salinities. Because of the lack of a genomic database, the scope of most studies, however, is very limited. Recently, our group reported the first high-throughput transcriptomic and proteomic studies to identify hyperosmotic-responsive genes/proteins in gills of Japanese eels. In this study, we aimed to decipher changes in hypo-osmotic-responsive proteins in fish acclimating from seawater (SW) to freshwater (FW) conditions. We collected gill samples from SW-adapted and SW-to-FW-acclimating fish. The respective gill proteins were extracted and labeled using isobaric tags for relative and absolute quantitation (iTRAQ) and analyzed using a high-resolution mass spectrometer. In the short-term transfer from SW to FW, 51 hypo-responsive proteins were detected, and 24 unique hypo-osmotic-responsive proteins were identified (15 up-regulated and nine down-regulated proteins). Our data support the use of an omics approach to facilitate the application of functional genomics in non-model organisms.

BIOLOGICAL SIGNIFICANCE

By combining transcriptomic and proteomic approaches, the study has provided the most comprehensive, targeted investigation of eel gill hypo-osmotic responsive proteins that provides molecular insights of osmoregulation mechanisms in a non-model organism, eel. This article is part of a Special Issue entitled: Proteomics of non-model organisms.

Proteomic changes between male and female worms of the polychaetous annelid Neanthes arenaceodentata before and after spawning

The Neanthesacuminata species complex (Polychaeta) are cosmopolitan in distribution. Neanthesarenaceodentata, Southern California member of the N. acuminata complex, has been widely used as toxicological test animal in the marine environment. Method of reproduction is unique in this polychaete complex. Same sexes fight and opposite sexes lie side by side until egg laying. Females lose about 75% of their weight and die after laying eggs. The male, capable of reproducing up to nine times, fertilizes the eggs and incubates the embryos for 3-4 weeks. The objective of this study was to determine if there is any set of proteins that influences this unique pattern of reproduction. Gel-based two-dimensional electrophoresis (2-DE) and gel-free quantitative proteomics methods were used to identify differential protein expression patterns before and after spawning in both male and female N. arenaceodentata. Males showed a higher degree of similarity in protein expression patterns but females showed large changes in phosphoproteme before and after spawning. There was a decrease (about 70%) in the number of detected phosphoproteins in spent females. The proteins involved in muscular development, cell signaling, structure and integrity, and translation were differentially expressed. This study provides proteomic insights of the male and female worms that may serve as a foundation for better understanding of unusual reproductive patterns in polychaete worms.

Novel animal defenses against predation: a snail egg neurotoxin combining lectin and pore-forming chains that resembles plant defense and bacteria attack toxins

Although most eggs are intensely predated, the aerial egg clutches from the aquatic snail Pomacea canaliculata have only one reported predator due to unparalleled biochemical defenses. These include two storage-proteins: ovorubin that provides a conspicuous (presumably warning) coloration and has antinutritive and antidigestive properties, and PcPV2 a neurotoxin with lethal effect on rodents. We sequenced PcPV2 and studied whether it was able to withstand the gastrointestinal environment and reach circulation of a potential predator. Capacity to resist digestion was assayed using small-angle X-ray scattering (SAXS), fluorescence spectroscopy and simulated gastrointestinal proteolysis. PcPV2 oligomer is antinutritive, withstanding proteinase digestion and displaying structural stability between pH 4.0-10.0. cDNA sequencing and protein domain search showed that its two subunits share homology with membrane attack complex/perforin (MACPF)-like toxins and tachylectin-like lectins, a previously unknown structure that resembles plant Type-2 ribosome-inactivating proteins and bacterial botulinum toxins. The protomer has therefore a novel AB toxin combination of a MACPF-like chain linked by disulfide bonds to a lectin-like chain, indicating a delivery system for the former. This was further supported by observing PcPV2 binding to glycocalix of enterocytes in vivo and in culture, and by its hemaggutinating, but not hemolytic activity, which suggested an interaction with surface oligosaccharides. PcPV2 is able to get into predator's body as evidenced in rats and mice by the presence of circulating antibodies in response to sublethal oral doses. To our knowledge, a lectin-pore-forming toxin has not been reported before, providing the first evidence of a neurotoxic lectin in animals, and a novel function for ancient and widely distributed proteins. The acquisition of this unique neurotoxic/antinutritive/storage protein may confer the eggs a survival advantage, opening new perspectives in the study of the evolution of animal defensive strategies.

Comparative analysis of circulating hemocytes of the freshwater snail Pomacea canaliculata

Molluscs are invertebrates of great relevance for economy, environment and public health. The numerous studies on molluscan immunity and physiology registered an impressive variability of circulating hemocytes. This study is focused on the first characterization of the circulating hemocytes of the freshwater gastropod Pomacea canaliculata, a model for several eco-toxicological and parasitological researches. Flow cytometry analysis identified two populations of hemocytes on the basis of differences in size and internal organization. The first population contains small and agranular cells. The second one displays major size and a more articulated internal organization. Light microscopy evidenced two principal morphologies, categorized as Group I (small) and II (large) hemocytes. Group I hemocytes present the characteristics of blast-like cells, with an agranular and basophilic cytoplasm. Group I hemocytes can adhere onto a glass surface but seem unable to phagocytize heat-inactivated Escherichia coli. The majority of Group II hemocytes displays an agranular cytoplasm, while a minority presents numerous granules. Agranular cytoplasm may be basophilic or acidophilic. Granules are positive to neutral red staining and therefore acidic. Independently from their morphology, Group II hemocytes are able to adhere and to engulf heat-inactivated E. coli. Transmission electron microscopy analysis clearly distinguished between agranular and granular hemocytes and highlighted the electron dense content of the granules. After hemolymph collection, time-course analysis indicated that the Group II hemocytes are subjected to an evident dynamism with changes in the percentage of agranular and granular hemocytes. The ability of circulating hemocytes to quickly modify their morphology and stainability suggests that P. canaliculata is endowed with highly dynamic hemocyte populations able to cope with rapid environmental changes as well as fast growing pathogens.

Transcriptome and quantitative proteome analysis reveals molecular processes associated with larval metamorphosis in the polychaete Pseudopolydora vexillosa

Larval growth of the polychaete worm Pseudopolydora vexillosa involves the formation of segment-specific structures. When larvae attain competency to settle, they discard swimming chaetae and secrete mucus. The larvae build tubes around themselves and metamorphose into benthic juveniles. Understanding the molecular processes, which regulate this complex and unique transition, remains a major challenge because of the limited molecular information available. To improve this situation, we conducted high-throughput RNA sequencing and quantitative proteome analysis of the larval stages of P. vexillosa. Based on gene ontology (GO) analysis, transcripts related to cellular and metabolic processes, binding, and catalytic activities were highly represented during larval-adult transition. Mitogen-activated protein kinase (MAPK), calcium-signaling, Wnt/β-catenin, and notch signaling metabolic pathways were enriched in transcriptome data. Quantitative proteomics identified 107 differentially expressed proteins in three distinct larval stages. Fourteen and 53 proteins exhibited specific differential expression during competency and metamorphosis, respectively. Dramatic up-regulation of proteins involved in signaling, metabolism, and cytoskeleton functions were found during the larval-juvenile transition. Several proteins involved in cell signaling, cytoskeleton and metabolism were up-regulated, whereas proteins related to transcription and oxidative phosphorylation were down-regulated during competency. The integration of high-throughput RNA sequencing and quantitative proteomics allowed a global scale analysis of larval transcripts/proteins associated molecular processes in the metamorphosis of polychaete worms. Further, transcriptomic and proteomic insights provide a new direction to understand the fundamental mechanisms that regulate larval metamorphosis in polychaetes.

Agglutinating activity and structural characterization of scalarin, the major egg protein of the snail Pomacea scalaris (d'Orbigny, 1832)

Apple snail perivitellins are emerging as ecologically important reproductive proteins. To elucidate if the protective functions of the egg proteins of Pomacea canaliculata (Caenogastropoda, Ampullariidae), involved in embryo defenses, are present in other Pomacea species we studied scalarin (PsSC), the major perivitellin of Pomacea scalaris. Using small angle X-ray scattering, fluorescence and absorption spectroscopy and biochemical methods, we analyzed PsSC structural stability, agglutinating activity, sugar specificity and protease resistance. PsSC aggluttinated rabbit, and, to a lesser extent, human B and A erythrocytes independently of divalent metals Ca(2+) and Mg(2+) were strongly inhibited by galactosamine and glucosamine. The protein was structurally stable between pH 2.0 to 10.0, though agglutination occurred only between pH 4.0 to 8.0 (maximum activity at pH 7.0). The agglutinating activity was conserved up to 60 °C and completely lost above 80 °C, in agreement with the structural thermal stability of the protein (up to 60 °C). PsSC was able to withstand in vitro gastrointestinal digestion, and showed no trypsin inhibition activity. The presence of lectin activity has been reported in eggs of other Pomacea snails, but here we link for the first time, this activity to an apple snail multifunctional perivitellin. This novel role for a snail egg storage protein is different from closely related P.canaliculata defensive proteins.