Proteomic Analysis of the Reproductive Organs of the Hermaphroditic Gastropod Lymnaea stagnalis Exposed to Different Endocrine Disrupting Chemicals

Effect of tributyltin exposure on the embryonic development and behavior of a molluscan model species, Lymnaea stagnalis

The presence of the organotin compound tributyltin (TBT) in aquatic ecosystems has been a serious environmental problem for decades. Although a number of studies described the negative impact of TBT on mollusks at different levels, investigations connected to its potential effects during embryogenesis have been neglected. For a better understanding of the impact of TBT on mollusks, in the present study, embryos of previously TBT-treated or not treated specimens of the great pond snail (Lymnaea stagnalis) were exposed to 100 ng L-1 TBT from egg-laying (single-cell stage) until hatching. According to our results, TBT significantly delayed hatching and caused shell malformation. TBT transiently decreased the locomotion (gliding) and also reduced the feeding activity, demonstrating for the first time that this compound can alter the behavioral patterns of molluscan embryos. The heart rate was also significantly reduced, providing further support that cardiac activity is an excellent indicator of metal pollution in molluscan species. At the histochemical level, tin was demonstrated for the first time in TBT-treated hatchlings with intensive reaction in the central nervous system, kidney, and hepatopancreas. Overall, the most notable effects were observed in treated embryos derived from TBT treated snails. Our findings indicate that TBT has detrimental effects on the development and physiological functions of Lymnaea embryos even at a sub-lethal concentration, potentially influencing their survival and fitness. Highlighting our observations, we have demonstrated previously unknown physiological changes (altered heart rate, locomotion, and feeding activity) caused by TBT, as well as visualized tin at the histochemical level in a molluscan species for the first time following TBT exposure. Further studies are in progress to reveal the cellular and molecular mechanisms underlying the physiological and behavioral changes described in the present study.

Lack of membrane sex steroid receptors for mediating rapid endocrine responses in molluscan nervous systems

Despite the lack of endogenous synthesis and relevant nuclear receptors, several papers have been published over the decades claiming that the physiology of mollusks is affected by natural and synthetic sex steroids. With scant evidence for the existence of functional steroid nuclear receptors in mollusks, some scientists have speculated that the effects of steroids might be mediated via membrane receptors (i.e. via non-genomic/non-classical actions) - a mechanism that has been well-characterized in vertebrates. However, no study has yet investigated the ligand-binding ability of such receptor candidates in mollusks. The aim of the present study was to further trace the evolution of the endocrine system by investigating the presence of functional membrane sex steroid receptors in a mollusk, the great pond snail (Lymnaea stagnalis). We detected sequences homologous to the known vertebrate membrane sex steroid receptors in the Lymnaea transcriptome and genome data: G protein-coupled estrogen receptor-1 (GPER1); membrane progestin receptors (mPRs); G protein-coupled receptor family C group 6 member A (GPRC6A); and Zrt- and Irt-like protein 9 (ZIP9). Sequence analyses, including conserved domain analysis, phylogenetics, and transmembrane domain prediction, indicated that the mPR and ZIP9 candidates appeared to be homologs, while the GPER1 and GPRC6A candidates seemed to be non-orthologous receptors. All candidates transiently transfected into HEK293MSR cells were found to be localized at the plasma membrane, confirming that they function as membrane receptors. However, the signaling assays revealed that none of the candidates interacted with the main vertebrate steroid ligands. Our findings strongly suggest that functional membrane sex steroid receptors which would be homologous to the vertebrate ones are not present in Lymnaea. Although further experiments are required on other molluscan model species as well, we propose that both classical and non-classical sex steroid signaling for endocrine responses are specific to chordates, confirming that molluscan and vertebrate endocrine systems are fundamentally different.

Yolk proteins of the schistosomiasis vector snail Biomphalaria glabrata revealed by multi-omics analysis

Vitellogenesis is the most important process in animal reproduction, in which yolk proteins play a vital role. Among multiple yolk protein precursors, vitellogenin (Vtg) is a well-known major yolk protein (MYP) in most oviparous animals. However, the nature of MYP in the freshwater gastropod snail Biomphalaria glabrata remains elusive. In the current study, we applied bioinformatics, tissue-specific transcriptomics, ovotestis-targeted proteomics, and phylogenetics to investigate the large lipid transfer protein (LLTP) superfamily and ferritin-like family in B. glabrata. Four members of LLTP superfamily (BgVtg1, BgVtg2, BgApo1, and BgApo2), one yolk ferritin (Bg yolk ferritin), and four soma ferritins (Bg ferritin 1, 2, 3, and 4) were identified in B. glabrata genome. The proteomic analysis demonstrated that, among the putative yolk proteins, BgVtg1 was the yolk protein appearing in the highest amount in the ovotestis, followed by Bg yolk ferritin. RNAseq profile showed that the leading synthesis sites of BgVtg1 and Bg yolk ferritin are in the ovotestis (presumably follicle cells) and digestive gland, respectively. Phylogenetic analysis indicated that BgVtg1 is well clustered with Vtgs of other vertebrates and invertebrates. We conclude that, vitellogenin (BgVtg1), not yolk ferritin (Bg yolk ferritin), is the major yolk protein precursor in the schistosomiasis vector snail B. glabrata.

Pesticide contamination in agro-ecosystems: toxicity, impacts, and bio-based management strategies

Continuous rise in application of pesticides in the agro-ecosystems in order to ensure food supply to the ever-growing population is of greater concern to the human health and the environment. Once entered into the agro-ecosystem, the fate and transport of pesticides is determined largely by the nature of pesticides and the soil attributes, in addition to the soil-inhabiting microbes, fauna, and flora. Changes in the soil microbiological actions, soil properties, and enzymatic activities resulting from pesticide applications are the important factors substantially affecting the soil productivity. Disturbances in the microbial community composition may lead to the considerable perturbations in cycling of major nutrients, metals, and subsequent uptake by plants. Indiscriminate applications are linked with the accumulation of pesticides in plant-based foods, feeds, and animal products. Furthermore, rapid increase in the application of pesticides having long half-life has also been reported to contaminate the nearby aquatic environments and accumulation in the plants, animals, and microbes surviving there. To circumvent the negative consequences of pesticide application, multitude of techniques falling in physical, chemical, and biological categories are presented by different investigators. In the present study, important findings pertaining to the pesticide contamination in cultivated agricultural soils; toxicity on soil microbes, plants, invertebrates, and vertebrates; effects on soil characteristics; and alleviation of toxicity by bio-based management approaches have been thoroughly reviewed. With the help of bibliometric analysis, thematic evolution and research trends on the bioremediation of pesticides in the agro-ecosystems have also been highlighted.

A combined bioinformatics and LC-MS based approach for the development and benchmarking of a comprehensive database of Lymnaea CNS proteins

Applications of key technologies in biomedical research, such as qRT-PCR or LC-MS based proteomics, are generating large biological (-omics) data sets which are useful for the identification and quantification of biomarkers in any research area of interest. Genome, transcriptome and proteome databases are already available for a number of model organisms including vertebrates and invertebrates. However, there is insufficient information available for protein sequences of certain invertebrates, such as the great pond snail Lymnaea stagnalis, a model organism that has been used highly successfully in elucidating evolutionarily conserved mechanisms of memory function and dysfunction. Here we used a bioinformatics approach to designing and benchmarking a comprehensive CNS proteomics database (LymCNS-PDB) for the identification of proteins from the CNS of Lymnaea by LC-MS based proteomics. LymCNS-PDB was created by using the Trinity TransDecoder bioinformatics tool to translate amino acid sequences from mRNA transcript assemblies obtained from a published Lymnaea transcriptomics database. The blast-style MMSeq2 software was used to match all translated sequences to UniProtKB sequences for molluscan proteins, including Lymnaea and other molluscs. LymCNS-PDB contains 9,628 identified matched proteins that were benchmarked by performing LC-MS based proteomics analysis with proteins isolated from the Lymnaea CNS. MS/MS analysis using the LymCNS-PDB database led to the identification of 3,810 proteins. Only 982 proteins were identified by using a non-specific molluscan database. LymCNS-PDB provides a valuable tool that will enable us to perform quantitative proteomics analysis of protein interactomes involved in several CNS functions in Lymnaea, including learning and memory and age-related memory decline.

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.

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.

Assessing the Impacts of Methoxychlor Exposure on the Viability, Reproduction, and Locomotor Behavior of the Seminole Ramshorn Snail (Planorbella duryi)

In the present study, the effects of short-term methoxychlor exposure on the viability, reproduction, and locomotor behavior of adult seminole ramshorn snails (Planorbella duryi) was assessed. To examine impacts on viability and behavior, individuals were exposed to a water control, vehicle control, or 12.5, 50, 100, 250, 500, or 1000 μg/L of methoxychlor for 48 h; and differences in mortality and locomotor behavior assessed using the freely available ToxTrac software. To determine impacts on reproduction, pairs of snails were exposed to a vehicle control and 12.5, 25, 50, 100, and 250 μg/L of methoxychlor for 9 d; and the number of clutches and eggs laid quantified every 24 h. Methoxychlor concentrations in treatments were determined using gas chromatography. Complete mortality was observed in the 500 μg/L and 1000 μg/L treatments after 48 h and in the 250 μg/L treatment after 9 d. Decreases in the number of egg clutches were observed in all treatments, and the number of eggs laid decreased starting in the 25 μg/L treatment. Decreases in average speed, mobile speed, and total distance traveled, as well as a significant increase in frozen events, were also observed. Our results suggest that methoxychlor exposure causes detrimental effects on several nonlethal endpoints in a nonmodel aquatic invertebrate species and that the analysis of locomotor behaviors serves as a reliable, sensitive endpoint for ecotoxicology testing. Environ Toxicol Chem 2019;39:220-228. © 2019 SETAC.

Lymnaea stagnalis as a freshwater model invertebrate for ecotoxicological studies

Lymnaea stagnalis, also referred to as great or common pond snail, is an abundant and widespread invertebrate species colonizing temperate limnic systems. Given the species importance, studies involving L. stagnalis have the potential to produce scientifically relevant information, leading to a better understanding of the damage caused by aquatic contamination, as well as the modes of action of toxicants. Lymnaea stagnalis individuals are easily maintained in laboratory conditions, with a lifespan of about two years. The snails are hermaphrodites and sexual maturity occurs about three months after egg laying. Importantly, they can produce a high number of offspring all year round and are considered well suited for use in investigations targeting the identification of developmental and reproductive impairments. The primary aims of this review were two-fold: i) to provide an updated and insightful compilation of established toxicological measures determined in both chronic and acute toxicity assays, as useful tool to the design and development of future research; and ii) to provide a state of the art related to direct toxicant exposure and its potentially negative effects on this species. Relevant and informative studies were analysed and discussed. Knowledge gaps in need to be addressed in the near future were further identified.

Disturbances in reproduction and expression of steroidogenic enzymes in aquatic invertebrates exposed to components of the herbicide Roundup

Exposure of organisms to environmental contaminants is a growing concern. We have investigated the effects of the individual active ingredients of the herbicide Roundup (glyphosate and diquat dibromide [DD]) since Roundup causes alterations in reproduction, mortality, and development in the aquatic snail Lymnaea palustris. Snails chronically treated with elevated but ecologically relevant levels of DD exhibit reduction in fecundity ( p < 0.05), while fecundity in glyphosate-treated snails is comparable to or exceeds control levels. To investigate a possible mechanism for the reproductive disturbance, we monitored levels of steroid acute regulatory (StAR) protein in whole snails and observed a correlation in StAR protein decrease with treatment with Roundup, glyphosate, or DD. We detect StAR in organs where steroid biosynthesis occurs (ovotestis, brain, kidney); StAR protein is reduced following chronic exposure to Roundup, glyphosate, or DD ( p < 0.01). Estradiol and testosterone concentrations in hemolymph were measured by enzyme-linked immunosorbent assay following 3-week exposure of snails to 3.5 mg/L glyphosate or 140 µg/L DD. Testosterone levels decrease in DD-treated groups ( p < 0.05); a trend of lower testosterone is also observed in glyphosate-treated groups ( p > 0.05). Estradiol concentration is greater than or equal to control levels in glyphosate, but decreased in DD ( p < 0.05). Because of its role in the conversion of testosterone to estradiol, we monitored abundance of aromatase and observed a reduction ( p < 0.05) in DD-treated snails (consistent with the drop in fecundity and estradiol levels) and a comparable level to control in glyphosate-treated snails (consistent with their high fecundity and estradiol levels). Although the toxicity of commercially-available Roundup to aquatic animals may have many contributing factors including its inactive surfactant, the constituent of Roundup associated with the greatest reproductive disturbances and observed developmental abnormalities of offspring is DD. This study details the analysis of particular herbicide constituents and their effect on specific targets in the reproductive pathway.

Adverse effects of the insecticides chlordecone and fipronil on population growth and expression of the entire cytochrome P450 (CYP) genes in the freshwater rotifer Brachionus calyciflorus and the marine rotifer Brachionus plicatilis

Chlordecone and fipronil are used as an insecticide and have been widely detected in the aquatic environments. However, their toxicity is still poorly investigated in aquatic invertebrates. In this study, we examined effects of chlordecone and fipronil on population growth and transcriptional regulation of the entire cytochrome P450 (CYP) genes in the freshwater rotifer Brachionus calyciflorus and the marine rotifer B. plicatilis. In B. calyciflorus, a 24 h-no observed effect concentration (NOEC-24 h) and a 24 h-median lethal concentration (LC50-24 h) of chlordecone were determined as 100 μg/L and 193.8 μg/L, respectively, while NOEC-24 h and LC50-24 h of fipronil were determined as 1000 μg/L and 2033.0 μg/L, respectively. In B. plicatilis, NOEC-24 h and LC50-24 h of chlordecone were 100 μg/L and 291.0 μg/L, respectively, while NOEC-24 h and LC50-24 h of fipronil were determined as 1000 μg/L and 5735.0 μg/L, respectively. Moreover, retardation in the population growth were observed in response to chlordecone and fipronil in both rotifer species, suggesting that chlordecone and fipronil have a potential adverse effects on life cycle parameters of two rotifer species. Additionally, modulation in the expressions of the entire CYP genes were demonstrated in response to chlordecone and fipronil at 24 h period. These results provide the better understanding on how chlordecone and fipronil can affect in population growth of two rotifers and CYP gene expressions in chlordecone- and fipronil-exposed rotifers.

Morphological and transcriptomic effects of endocrine modulators on the gonadal differentiation of chicken embryos: The case of tributyltin (TBT)

Morphological malformations induced by tributyltin (TBT) exposure during embryonic development have already been characterized in various taxonomic groups, but, nonetheless, the molecular processes underlying these changes remain obscure. The present study provides the first genome-wide screening for differentially expressed genes that are linked to morphological alterations of gonadal tissue from chicken embryos after exposure to TBT. We applied a single injection of TBT (between 0.5 and 30 pg as Sn/g egg) into incubated fertile eggs to simulate maternal transfer of the endocrine disruptive compound. Methyltestosterone (MT) served as a positive control (30 pg/g egg). After 19 days of incubation, structural features of the gonads as well as genome-wide gene expression profiles were assessed simultaneously. TBT induced significant morphological and histological malformations of gonadal tissue from female embryos that show a virilization of the ovaries. This phenotypical virilization was mirrored by altered expression profiles of sex-dependent genes. Among these are several transcription and growth factors (e.g. FGF12, CTCF, NFIB), whose altered expression might serve as a set of markers for early identification of endocrine active chemicals that affect embryonic development by transcriptome profiling without the need of elaborate histological analyses.

Effect of progesterone and its synthetic analogs on reproduction and embryonic development of a freshwater invertebrate model

The presence of a mixture of progestogens at ng/L concentration levels in surface waters is a worldwide problem. Only a few studies explore the effect of progestogen treatment in a mixture as opposed to individual chemicals to shed light on how non-target species respond to these contaminants. In the present study, we used an invertebrate model species, Lymnaea stagnalis, exposed to a mixture of four progestogens (progesterone, levonorgestrel, drospirenone, and gestodene) in 10ng/L concentration for 3 weeks. Data at both physiological and cellular/molecular level were analyzed using the ELISA technique, stereomicroscopy combined with time lapse software, and capillary microsampling combined with mass spectrometry. The treatment of adult Lymnaeas caused reduced egg production, and low quality egg mass on the first week, compared to the control. Starting from the second week, the egg production, and the quality of egg mass were similar in both groups. At the end of the third week, the egg production and the vitellogenin-like protein content of the hepatopancreas were significantly elevated in the treated group. At the cellular level, accelerated cell proliferation was observed during early embryogenesis in the treated group. The investigation of metabolomic changes resulted significantly elevated hexose utilization in the single-cell zygote cytoplasm, and elevated adenylate energy charge in the egg albumen. These changes suggested that treated snails provided more hexose in the eggs in order to improve offspring viability. Our study contributes to the knowledge of physiological effect of equi-concentration progestogen mixture at environmentally relevant dose on non-target aquatic species.

Assessing the dynamic changes of rhizosphere functionality of Zea mays plants grown in organochlorine contaminated soils

The persistent organochlorine pesticides (OCPs) in soils are suspected to disturb soil biogeochemical cycles. This study addressed the dynamic changes in soil functionality under lindane and chlordecone exposures with or without maize plant. Decreases in soil ammonium concentration, potential nitrogen mineralization and microbial biomass were only OCP-influenced in bulk soils. OCPs appeared to inhibit the ammonification step. With plants, soil functionality under OCP stress was similar to controls demonstrating the plant influence to ensure the efficiency of C- and N-turnover in soils. Moreover, OCPs did not impact the microbial community physiological profile in all tested conditions. However, microbial community structure was OCP-modified only in the presence of plants. Abundances of gram-negative and saprophytic fungi increased (up to +93% and +55%, respectively) suggesting a plant stimulation of nutrient turnover and rhizodegradation processes. Nevertheless, intimate microbial/plant interactions appeared to be OCP-impacted with depletions in mycorrhizae and micro/meso-fauna abundances (up to -53% and -56%, respectively) which might have adverse effects on more long-term plant growth (3-4 months). In short-term experiment (28days), maize growth was similar to the control ones, indicating an enhanced plasticity of the soil functioning in the presence of plants, which could efficiently participate to the remediation of OCP-contaminated soils.

Ecotoxicoproteomic assessment of the functional alterations caused by chronic metallic exposures in gammarids

Very few ecotoxicological studies have been performed on long-term exposure under controlled conditions, hence limiting the assessment of the impact of chronic and diffuse chemical pressures on the health of aquatic organisms. In this study, an ecotoxicoproteomic approach was used to assess the integrated response and possible acclimation mechanisms in Gammarus fossarum following chronic exposures to Cd, Cu or Pb, at environmentally realistic concentrations (i.e. 0.25, 1.5 and 5 μg/L respectively). After 10-week exposure, changes in protein expression were investigated in caeca of control and exposed males. Gel-free proteomic analyses allowed for the identification of 35 proteins involved in various biological functions, for which 23 were significantly deregulated by metal exposures. The protein deregulation profiles were specific to each metal, providing evidence for metal-specific action sites and responses of gammarids. Among the tested metals, Cu was the most toxic in terms of mortality, probably linked with persistent oxidative stress. Moulting and osmoregulation were the major biological functions affected by Cu in the long-term. In Pb-exposed gammarids, significant deregulations of proteins involved in immune response and cytoskeleton were observed. Reproduction appears to be strongly affected in gammarids chronically exposed to Cd or Pb. Besides, modified expressions of several proteins involved in energy transfer and metabolism highlighted important energetic reshuffling to cope with chronic metal exposures. These results support the fact that metallic pressures induce a functional and energetic cost for individuals of G. fossarum with potential repercussions on population dynamics. Furthermore, this ecotoxicoproteomic study offers promising lines of enquiry in the development of new biomarkers that could make evidence of long-term impacts of metals on the health of organisms.

Biomarkers of inflammation and innate immunity in atrophic nonunion fracture

BACKGROUND

Nonunion is a failure of healing following a bone fracture. Its physiopathology remains partially unclear and the discovery of new mediators could promote the understanding of bone healing.

METHODS

Thirty-three atrophic nonunion (NU) patients that failed to demonstrate any radiographic improvement for 6 consecutive months were recruited for providing serum samples. Thirty-five healthy volunteers (HV) served as the control group. Proteomics studies were performed using SELDI-TOF-MS and 2D-DIGE approaches, associated or not with Proteominer® preprocessing, to highlight biomarkers specific to atrophic nonunion pathology. Peak intensities were analyzed by two statistical approaches, a nonparametric Mann-Whitney U tests (univariate approach) and a machine-learning algorithm called extra-trees (multivariate approach). Validation of highlighted biomarkers was performed by alternative approaches such as microfluidic LC-MS/MS, nephelometry, western blotting or ELISA assays.

RESULTS

From the 35 HV and 33 NU crude serum samples and Proteominer® eluates, 136 spectra were collected by SELDI-TOF-MS using CM10 and IMAC-Cu(2+) ProteinChip arrays, and 665 peaks were integrated for extra-trees multivariate analysis. Accordingly, seven biomarkers and several variants were identified as potential NU biomarkers. Their levels of expression were found to be down- or up-regulated in serum of HV vs NU. These biomarkers are inter-α-trypsin inhibitor H4, hepcidin, S100A8, S100A9, glycated hemoglobin β subunit, PACAP related peptide, complement C3 α-chain. 2D-DIGE experiment allowed to detect 14 biomarkers as being down- or up-regulated in serum of HV vs NU including a cleaved fragment of apolipoprotein A-IV, apolipoprotein E, complement C3 and C6. Several biomarkers such as hepcidin, complement C6, S100A9, apolipoprotein E, complement C3 and C4 were confirmed by an alternative approach as being up-regulated in serum of NU patients compared to HV controls.

CONCLUSION

Two proteomics approaches were used to identify new biomarkers up- or down-regulated in the nonunion pathology, which are involved in bone turn-over, inflammation, innate immunity, glycation and lipid metabolisms. High expression of hepcidin or S100A8/S100A9 by myeloid cells and the presence of advanced glycation end products and complement factors could be the result of a longstanding inflammatory process. Blocking macrophage activation and/or TLR4 receptor could accelerate healing of fractured bone in at-risk patients.

Steroid Androgen Exposure during Development Has No Effect on Reproductive Physiology of Biomphalaria glabrata

Gastropod mollusks have been proposed as alternative models for male reproductive toxicity testing, due to similarities in their reproductive anatomy compared to mammals, together with evidence that endocrine disrupting chemicals can cause effects in some mollusks analogous to those seen in mammals. To test this hypothesis, we used the freshwater pulmonate snail, Biomphalaria glabrata, for which various genetic tools and a draft genome have recently become available, to investigate the effects of two steroid androgens on the development of mollusk secondary sexual organs. Here we present the results of exposures to two potent androgens, the vertebrate steroid; 5α-dihydrotestosterone (DHT) and the pharmaceutical anabolic steroid; 17α-methyltestosterone (MT), under continuous flow-through conditions throughout embryonic development and up to sexual maturity. Secondary sexual gland morphology, histopathology and differential gene expression analysis were used to determine whether steroid androgens stimulated or inhibited organ development. No significant differences between tissues from control and exposed snails were identified, suggesting that these androgens elicited no biologically detectable response normally associated with exposure to androgens in vertebrate model systems. Identifying no effect of androgens in this mollusk is significant, not only in the context of the suitability of mollusks as alternative model organisms for testing vertebrate androgen receptor agonists but also, if applicable to other similar mollusks, in terms of the likely impacts of androgens and anti-androgenic pollutants present in the aquatic environment.

Transcriptome analysis of the copepod Eurytemora affinis upon exposure to endocrine disruptor pesticides: Focus on reproduction and development

Copepods-which include freshwater and marine species-represent the most abundant group of aquatic invertebrates. Among them, the calanoid copepod Eurytemora affinis is widely represented in the northern hemisphere estuaries and has become a species of interest in ecotoxicology. Like other non-target organisms, E. affinis may be exposed to a wide range of chemicals such as endocrine disruptors (EDs). This study investigated the gene expression variation in E. affinis after exposure to ED pesticides-chosen as model EDs-in order to (i) improve the knowledge on their effects in crustaceans, and (ii) highlight relevant transcripts for further development of potential biomarkers of ED exposure/effect. The study focused on the reproduction function in response to ED. Copepods were exposed to sublethal concentrations of pyriproxyfen (PXF) and chlordecone (CLD) separately. After 48h, males and females (400 individuals each) were sorted for RNA extraction. Their transcriptome was pyrosequenced using the Illumina(®) technology. Contigs were blasted and functionally annotated using Blast2GO(®). The differential expression analysis between ED- and acetone-exposed organisms was performed according to sexes and contaminants. Half of the 19,721 contigs provided by pyrosequencing were annotated, mostly (80%) from arthropod sequences. Overall, 2,566 different genes were differentially expressed after ED exposures in comparison with controls. As many genes were differentially expressed after PXF exposure as after CLD exposure. In contrast, more genes were differentially expressed in males than in females after both exposures. Ninety-seven genes overlapped in all conditions. Finally, 31 transcripts involved in reproduction, growth and development, and changed in both chemical exposures were selected as potential candidates for future development of biomarkers.

Effects of chlordecone on 20-hydroxyecdysone concentration and chitobiase activity in a decapod crustacean, Macrobrachium rosenbergii

Chlordecone (CLD) is an organochlorine insecticide abundant in aquatic environment of the French West Indies. However, few studies have investigated its impact on freshwater invertebrates. Whereas CLD is suspected of inducing endocrine disruption, this work aimed to study the effects of environmentally relevant concentrations of CLD on the 20-hydroxyecdysone (20-HE) hormone concentration and on the chitobiase activity, both having key roles in the molting process of crustaceans. In addition, the bioaccumulation of CLD was measured in the muscle tissue of Macrobrachium rosenbergii to underline potential dose-response relationship. The results have shown that CLD was bioaccumulated in exposed organisms according to a trend to a dose-response relationship. Moreover, it was observed that CLD decreased the 20-HE concentration in exposed prawns when compared to control, whatever the duration of exposure, as well as it inhibited the chitobiase activity after 30days of exposure. The present study indicates that CLD could interfere with molting process of M. rosenbergii by disturbing the 20-HE concentration and the activity of chitobiase, suggesting consequences at the long term on the shrimp development. This study also confirmed that CLD could be an endocrine disruptor in decapod crustaceans, as it was already observed in vertebrates.

Time course of lead induced proteomic changes in gill of the Antarctic limpet Nacella Concinna (Gastropoda: Patellidae)

The effect of increasing levels of metals from anthropogenic sources on Antarctic invertebrates is poorly understood. Here we exposed limpets (Nacella concinna) to 0, 0.12 and 0.25 μg L− 1 lead for 12, 24, 48 and 168 h. We subsequently quantified the changes in protein abundance from gill, using 2D gel electrophoresis and mass spectrometry. We identified several antioxidant proteins, including the metal binding Mn-superoxide dismutase and ferritin, increasing abundances early on. Chaperones involved in the redox-dependent maturation of proteins in the endoplasmic reticulum (ER) showed higher abundance with lead at 48 h. Lead also increased the abundance of Zn-binding carbonic anhydrase at 12 h, suggesting a challenge to acid-base balance. Metabolic proteins increased abundance at 168 h, suggesting a greater ATP demand during prolonged exposure. Changes in abundance of the small G-protein cdc42, a signaling protein modifying cytoskeleton, increased early and subsequently reversed during prolonged exposure, possibly leading to the modification of thick filament structure and function. We hypothesize that the replacement of metals initially affected antioxidant proteins and increased the production of reactive oxygen species. This disrupted the redox-sensitive maturation of proteins in the ER and caused increased ATP demand later on, accompanied by changes in cytoskeleton.

SIGNIFICANCE

Proteomic analysis of gill tissue in Antarctic limpets exposed to different concentrations of lead (Pb) over a 168 h time period showed that proteomic changes vary with time. These changes included an increase in the demand of scavenging reactive oxygen species, acid-base balance and a challenge to protein homeostasis in the endoplasmic reticulum early on and subsequently an increase in energy metabolism, cellular signaling, and cytoskeletal modifications. Based on this time course, we hypothesize that the main mode of action of lead is a replacement of metal-cofactors of key enzymes involved in the scavenging of reactive oxygen species and the regulation of acid-base balance.

Gender differences in responses in Gammarus pulex exposed to BDE-47: A gel-free proteomic approach

Very few ecotoxicological studies have considered differences in toxic effects on male and female organisms. Here, we investigated protein expression differences in caeca of Gammarus pulex males and females under control conditions (unexposed) and after 96h exposure to BDE-47. Using gel-free proteomic analysis, we have identified 45 proteins, of which 25 were significantly differently expressed according to sex and/or BDE-47 exposure. These proteins were involved in several biological processes such as energy metabolism, chaperone proteins, or transcription/translation. In unexposed amphipods, 11 proteins were significantly over-expressed in females, and 6 proteins were over-expressed in males. Under BDE-47 stress, 7 proteins were differently impacted according to sex. For example, catalase was over-expressed in exposed females and under-expressed in exposed males, as compared to respective controls. Conversely, proteins involved in energy metabolism were up-regulated in males and down-regulated in females. Our proteomic study showed differences in responses of males and females to BDE-47 exposure, emphasizing that sex is a confounding factor in ecotoxicological assessment. However, due to the limited information existing in databases on Gammarids, it was difficult to define a BDE-47 mechanism of action. The gel-free proteomic seems to be a promising method to develop in future ecotoxicological studies and thus, to improve our understanding of the mechanism of action of xenobiotics.

Altered Gene Expression in the Schistosome-Transmitting Snail Biomphalaria glabrata following Exposure to Niclosamide, the Active Ingredient in the Widely Used Molluscicide Bayluscide

In view of the call by the World Health Organization (WHO) for elimination of schistosomiasis as a public health problem by 2025, use of molluscicides in snail control to supplement chemotherapy–based control efforts is likely to increase in the coming years. The mechanisms of action of niclosamide, the active ingredient in the most widely used molluscicides, remain largely unknown. A better understanding of its toxicology at the molecular level will both improve our knowledge of snail biology and may offer valuable insights into the development of better chemical control methods for snails. We used a recently developed Biomphalaria glabrata oligonucleotide microarray (31K features) to investigate the effect of sublethal exposure to niclosamide on the transcriptional responses of the snail B. glabrata relative to untreated snails. Most of the genes highly upregulated following exposure of snails to niclosamide are involved in biotransformation of xenobiotics, including genes encoding cytochrome P450s (CYP), glutathione S-transferases (GST), and drug transporters, notably multi-drug resistance protein (efflux transporter) and solute linked carrier (influx transporter). Niclosamide also induced stress responses. Specifically, six heat shock protein (HSP) genes from three super-families (HSP20, HSP40 and HSP70) were upregulated. Genes encoding ADP-ribosylation factor (ARF), cAMP response element-binding protein (CREB) and coatomer, all of which are involved in vesicle trafficking in the Golgi of mammalian cells, were also upregulated. Lastly, a hemoglobin gene was downregulated, suggesting niclosamide may affect oxygen transport. Our results show that snails mount substantial responses to sublethal concentrations of niclosamide, at least some of which appear to be protective. The topic of how niclosamide’s lethality at higher concentrations is determined requires further study. Given that niclosamide has also been used as an anthelmintic drug for decades and has been found to have activity against several types of cancer, our findings may be of relevance in understanding how both parasites and neoplastic cells respond to this compound.

Schistosomes are snail-transmitted parasites that continue to infect over 230 million people worldwide and cause the disease schistosomiasis. Currently there is no effective vaccine against the disease. Control programs have relied primarily on use of chemotherapy with praziquantel to eliminate adult worms from infected people. An increasing body of evidence, however, suggests that praziquantel-based control programs are not likely to be sufficient to achieve sustainable transmission control. Snail control achieved by focal use of molluscicides, especially in combination with other methods like chemotherapy, sanitation and health education, offers considerable promise for reduction of disease transmission. Consequently, use of molluscicides in snail control is likely to increase in the coming years. We undertook a microarray study to assess transcriptional responses to niclosamide, the active ingredient in commonly-used molluscicides, in the schistosome-transmitting snail Biomphalaria glabrata. We show that niclosamide activates components in snails’ pathways known to be involved in biotransformation of xenobiotics and stress responses. We suggest that major alterations in vesicle trafficking and interference with oxygen transport also follow niclosamide exposure. The results contribute to our understanding of molecular impacts of niclosamide exposure on snails, and provide a basis for further studies to define the mode of action of niclosamide and other molluscicides in the future.

Expression of biotransformation and oxidative stress genes in the giant freshwater prawn Macrobrachium rosenbergii exposed to chlordecone

Chlordecone is a persistent organochlorine pesticide widely used between 1972 and 1993 in the French West Indies to control the root borer in banana fields. Chlordecone use resulted in long-term pollution of soils, contamination of waters, of aquatic organisms, and of fields. Chlordecone is known to be neurotoxic, to increase prostate cancer, and to have negative effects on cognitive and motor development during infancy. In Guadeloupe, most of the freshwater species living in contaminated rivers exceed the French legal limit of 20 μg·kg(-1) wet weight. In the present study, we chose a transcriptomic approach to study the cellular effects of chlordecone in the giant freshwater prawn Macrobrachium rosenbergii, an important economical species in Guadeloupe. Quantitative PCR revealed an induction of genes involved in defense mechanism against oxidative stress (catalase and selenium-dependent glutathione peroxidase) in prawns exposed to low environmental concentrations of chlordecone after 12 and 24 h of exposure. In prawns reared in a contaminated farm, transcription of genes involved in the biotransformation process (cytochrome P450 and glutathione-S-transferase (GST)) were induced after 8 days of exposure. Our results provide information on the mechanims of defense induced by chlordecone in aquatic crustacean species. This gene expression study of selected genes should be further strengthened by proteomic analyses and enzymatic activity assays to confirm the response of these biomarkers of stress in crustaceans and to give new insights into the mechanism of toxicity by chlordecone.

Developmental toxicity, acute toxicity and mutagenicity testing in freshwater snails Biomphalaria glabrata (Mollusca: Gastropoda) exposed to chromium and water samples

A protocol combining acute toxicity, developmental toxicity and mutagenicity analysis in freshwater snail Biomphalaria glabrata for application in ecotoxicological studies is described. For acute toxicity testing, LC50 and EC50 values were determined; dominant lethal mutations induction was the endpoint for mutagenicity analysis. Reference toxicant potassium dichromate (K2Cr2O7) was used to characterize B. glabrata sensitivity for toxicity and cyclophosphamide to mutagenicity testing purposes. Compared to other relevant freshwater species, B. glabrata showed high sensitivity: the lowest EC50 value was obtained with embryos at veliger stage (5.76mg/L). To assess the model applicability for environmental studies, influent and effluent water samples from a wastewater treatment plant were evaluated. Gastropod sensitivity was assessed in comparison to the standardized bioassay with Daphnia similis exposed to the same water samples. Sampling sites identified as toxic to daphnids were also detected by snails, showing a qualitatively similar sensitivity suggesting that B. glabrata is a suitable test species for freshwater monitoring. Holding procedures and protocols implemented for toxicity and developmental bioassays showed to be in compliance with international standards for intra-laboratory precision. Thereby, we are proposing this system for application in ecotoxicological studies.

Investigating apical adverse effects of four endocrine active substances in the freshwater gastropod Lymnaea stagnalis

The hermaphroditic gastropod Lymnaea stagnalis is proposed as a candidate species for the development of OECD guidelines for testing of the reprotoxicity of chemicals, including endocrine active substances (EASs). Up to now, only a few putative EASs have been tested for their reproductive toxicity in this species. In this study, we investigate the effects of four EASs with different affinities to the vertebrate estrogen and androgen receptors (chlordecone as an estrogen; cyproterone acetate, fenitrothion and vinclozolin as anti-androgens) on the reproduction of L. stagnalis in a 21-day semi-static test. Testosterone and 17α-ethinylestradiol (EE2) were used as the reference compounds. The tested EASs had no significant effect on growth and survival at the tested concentration ranges (ng to μg/L). Classical reproduction endpoints (i.e., oviposition and fecundity) were not responsive to the tested chemicals, except for chlordecone and 17α-ethinylestradiol, which hampered reproduction from 19.6 μg/L and 17.6 μg/L, respectively. The frequency of polyembryonic eggs, used as an additional endpoint, demonstrated the effects of all compounds except EE2. The molecular pathways, which are involved in such reproduction impairments, remain unknown. Our results suggest that egg quality is a more sensitive endpoint as compared to other reproductive endpoints commonly assessed in mollusk toxicity tests.