Do mollusks use vertebrate sex steroids as reproductive hormones? Part I: Critical appraisal of the evidence for the presence, biosynthesis and uptake of steroids

Toxicity and bioconcentration of bisphenol A alternatives in the freshwater pulmonate snail Planorbella pilsbryi

Bisphenol A (BPA) is an industrial chemical identified as a vertebrate endocrine disruptor. Numerous alternatives have been developed, for which toxicity data are lacking. The present study assessed the toxicity of BPA and its replacement products bisphenol F (BPF), bisphenol S (BPS), and bisphenol AF (BPAF) in freshwater snail (Planorbella pilsbryi) embryos and adults. The chronic toxicity of BPA and BPAF was further characterized in 28-day tests with adult snails, followed by 21-day assessments of hatching and survival of embryos produced at the end of the test (F1 generation). In acute tests, BPAF was the most toxic of the substances tested (maximum acceptable toxicant concentration [MATC], 136 µg/L), followed by BPA (MATC, 1404 µg/L), BPF (MATC, 1525 µg/L), and BPS (MATC > 8590 µg/L). In the chronic test with BPA, although we observed no significant effects on adult snails up to 479 µg/L, the hatching and survival of juveniles from the F1 generation decreased (MATC, 13 µg/L), and was delayed by 7.5 days, on average. In contrast, we did not observe any decrease in hatching or survival of juveniles from the F1 generation during exposure to BPAF. Effects were observed at concentrations above most reported environmental exposure concentrations, although there was an overlap between exposure and effect concentrations. Given that concentrations of alternative substances are expected to increase, and in the absence of data on potential effects of mixtures, further research is needed.

Studies on cortisol, corticosterone, and 17β-estradiol indicate these steroids have no role in stress or reproduction in the common octopus (Octopus vulgaris)

The common octopus (Octopus vulgaris) is a promising candidate for aquaculture diversification, particularly in Europe. As interest in octopus farming grows, animal welfare concerns arise. In bony vertebrates (teleosts and tetrapods), measurements of the levels of corticosterone or cortisol have been successfully used as indicators of stress and welfare. Here, it is explored whether octopuses also produce cortisol or corticosterone and, if so, whether they are released into the water in response to stress (as can be done in teleosts and amphibians). The ability of the octopus to absorb cortisol from the water is also investigated-with another steroid, the principle vertebrate estrogen, 17β-estradiol (E2), being used as a positive uptake control. In this study, using liquid chromatography tandem mass spectrometry techniques, it was found that octopus hemolymph did not contain either cortisol, corticosterone, cortisone (a common metabolite of cortisol), or E2. Nor were any of the corticosteroids consistently found in the water in which stressed octopuses were held. The results support the evolutionary argument that octopuses are unlikely to exhibit a stress response mediated by vertebrate-like corticosteroids. Octopus demonstrated a low ability to absorb cortisol from the water (<2% over 24 h) but showed a high ability to absorb E2 from water (92% over 24 h). In this latter respect, the octopus is similar to other mollusks. The finding calls into doubt the origin of the E2 measured in this species.NEW & NOTEWORTHY This study demonstrates that common octopuses (Octopus vulgaris Cuvier 1797) do not produce cortisol, cortisone, or corticosterone in response to stress. Using liquid chromatography tandem mass spectrometry, it was also shown that octopuses have a low absorption rate of cortisol from water but a high absorption rate of 17β-estradiol (E2). The findings support the evolutionary argument that octopuses are unlikely to exhibit a stress response mediated by vertebrate-like corticosteroids.

The effect of sex hormones on sex inversion in the mussel Mytilusgalloprovincialis

Global changes in the coastal ecosystems of oceans and seas, influenced by natural environmental factors and anthropogenic load, have led to a shift in the sexual structure of the mussel Mytilus galloprovincialis, a species cultivated in many countries. This paper is the first to study the effects of steroid hormones on sex inversion and mortality in the M. galloprovincialis. A unidirectional pattern of sex change from females to males was observed. A 100% sex change of females was achieved under the influence of the hormone testosterone during the period of post-spring restructuring of the gonads. No sex change occurred when males and females were exposed to 17β-estradiol. The mortality of mollusks did not exceed 5%.

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.

Is there potential for estradiol receptor signaling in lophotrochozoans?

Estrogen receptors (ERs) are thought to be the ancestor of all steroid receptors and are present in most lophotrochozoans studied to date, including molluscs, annelids, and rotifers. A number of studies have investigated the functional role of estrogen receptors in invertebrate species, although most are in molluscs, where the receptor is constitutively active. In vitro experiments provided evidence for ligand-activated estrogen receptors in annelids, raising important questions about the role of estrogen signalling in lophotrochozoan lineages. Here, we review the concordant and discordant evidence of estradiol receptor signalling in lophotrochozoans, with a focus on annelids and rotifers. We explore the de novo synthesis of estrogens, the evolution and expression of estrogen receptors, and physiological responses to activation of estrogen receptors in the lophotrochozoan phyla Annelida and Rotifera. Key data are missing to determine if de novo biosynthesis of estradiol in non-molluscan lophotrochozoans is likely. For example, an ortholog for the CYP11 gene is present, but confirmation of substrate conversion and measured tissue products is lacking. Orthologs CYP17 and CYP19 are lacking, yet intermediates or products (e.g. estradiol) in tissues have been measured. Estrogen receptors are present in multiple species, and for a limited number, in vitro data show agonist binding of estradiol and/or transcriptional activation. The expression patterns of the lophotrochozoan ERs suggest developmental, reproductive, and digestive roles but are highly species dependent. E2 exposures suggest that lophotrochozoan ERs may play a role in reproduction, but no strong dose-response relationship has been established. Therefore, we expect most lophotrochozoan species, outside of perhaps platyhelminths, to have an ER but their physiological role remains elusive. Mining genomes for orthologs gene families responsible for steroidogenesis, coupled with in vitro and in vivo studies of the steroid pathway are needed to better assess whether lophotrochozoans are capable of estradiol biosynthesis. One major challenge is that much of the data are divided across a diversity of species. We propose that the polychaetes Capitella teleta or Platyneris dumerilii, and rotifer Brachionus manjavacas may be strong species choices for studies of estrogen receptor signalling, because of available genomic data, established laboratory culture techniques, and gene knockout potential.

In silico structural features of the CgNR5A: CgDAX complex and its role in regulating gene expression of CYP target genes in Crassostrea gigas

Contamination of aquatic environments has been steadily increasing due to human activities. The Pacific oyster Crassostrea gigas has been used as a key species in studies assessing the impacts of contaminants on human health and the aquatic biome. In this context, cytochrome P450 (CYPs) play a crucial role in xenobiotic metabolism. In vertebrates many of these CYPs are regulated by nuclear receptors (NRs) and little is known about the NRs role in C. gigas. Particularly, the CgNR5A represents a homologue of SF1 and LRH-1 found in vertebrates. Members of this group can regulate genes of CYPs involved in lipid/steroid metabolism, with their activity regulated by other NR, called as DAX-1, generating a NR complex on DNA response elements (REs). As C. gigas does not exhibit steroid biosynthesis pathways, CgNR5A may play other physiological roles. To clarify this issue, we conducted an in silico investigation of the interaction between CgNR5A and DNA to identify potential C. gigas CYP target genes. Using molecular docking and dynamics simulations of the CgNR5A on DNA molecules, we identified a monomeric interaction with extended REs. This RE was found in the promoter region of 30 CYP genes and also the NR CgDAX. When the upstream regulatory region was analyzed, CYP2C39, CYP3A11, CYP4C21, CYP7A1, CYP17A1, and CYP27C1 were mapped as the main genes regulated by CgNR5A. These identified CYPs belong to families known for their involvement in xenobiotic and lipid/steroid metabolism. Furthermore, we reconstructed a trimeric complex, previously proposed for vertebrates, with CgNR5A:CgDAX and subjected it to molecular dynamics simulations analysis. Heterotrimeric complex remained stable during the simulations, suggesting that CgDAX may modulate CgNR5A transcriptional activity. This study provides insights into the potential physiological processes involving these NRs in the regulation of CYPs associated with xenobiotic and steroid/lipid metabolism.

Exploring BPA alternatives - Environmental levels and toxicity review

Bisphenol A alternatives are manufactured as potentially less harmful substitutes of bisphenol A (BPA) that offer similar functionality. These alternatives are already in the market, entering the environment and thus raising ecological concerns. However, it can be expected that levels of BPA alternatives will dominate in the future, they are limited information on their environmental safety. The EU PARC project highlights BPA alternatives as priority chemicals and consolidates information on BPA alternatives, with a focus on environmental relevance and on the identification of the research gaps. The review highlighted aspects and future perspectives. In brief, an extension of environmental monitoring is crucial, extending it to cover BPA alternatives to track their levels and facilitate the timely implementation of mitigation measures. The biological activity has been studied for BPA alternatives, but in a non-systematic way and prioritized a limited number of chemicals. For several BPA alternatives, the data has already provided substantial evidence regarding their potential harm to the environment. We stress the importance of conducting more comprehensive assessments that go beyond the traditional reproductive studies and focus on overlooked relevant endpoints. Future research should also consider mixture effects, realistic environmental concentrations, and the long-term consequences on biota and ecosystems.

Toxic Relationships: Prediction of TBT's Affinity to the Ecdysteroid Receptor of Triops longicaudatus

Tributyltin (TBT) is a biocide introduced in the 1960s in antifouling paints. Despite legislation banning its use, its persistence in the environment still causes significant harm to organisms. Tributyltin is a ligand of retinoid X receptors (RXR) and ecdysteroid receptors (EcRs), which in arthropods act as homologs of RXR. Focusing on Metazoan species, this study used genomic and proteomic information from different sources to compare their three-dimensional structure, phylogenetic distribution, and amino acid sequence alterations. The objective was to identify possible patterns that relate organisms' sensitivity to TBT using the species Triops longicaudatus as the basis for the comparisons. The results showed great conservation of this protein across several species when comparing the interaction amino acids described to RXR (an EcR analog) in Homo sapiens. The three-dimensional comparison of RXR showed little conformational variation between different sequences by maintaining the interaction pocket. As for the Species Sensitivity Distribution (SSD) curve, an HC05 = 0.2649 [0.0789-0.7082] µg/L was obtained with no specific distribution between the different taxa. Protein-ligand docking analysis was then used to confirm the SSD curve ranking of species. Still, the results showed an opposite trend that may be related, for example, to differences in the LC50 values used in the calculations. This study serves as the first step for applying bioinformatics techniques to produce information that can be used as an alternative to animal or cellular experimentation. These techniques could be adapted to various chemicals and proteins, allowing for observations in a shorter timeframe and providing information on a broader spectrum.

Insights on the Organ-Dependent, Molecular Sexual Dimorphism in the Zebra Mussel, Dreissena polymorpha, Revealed by Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry Metabolomics

The zebra mussel, Dreissena polymorpha, is extensively used as a sentinel species for biosurveys of environmental contaminants in freshwater ecosystems and for ecotoxicological studies. However, its metabolome remains poorly understood, particularly in light of the potential molecular sexual dimorphism between its different tissues. From an ecotoxicological point of view, inter-sex and inter-organ differences in the metabolome suggest variability in responsiveness, which can influence the analysis and interpretation of data, particularly in the case where males and females would be analyzed indifferently. This study aimed to assess the extent to which the molecular fingerprints of functionally diverse tissues like the digestive glands, gonads, gills, and mantle of D. polymorpha can reveal tissue-specific molecular sexual dimorphism. We employed a non-targeted metabolomic approach using liquid chromatography high-resolution mass spectrometry and revealed a significant sexual molecular dimorphism in the gonads, and to a lesser extent in the digestive glands, of D. polymorpha. Our results highlight the critical need to consider inter-sex differences in the metabolome of D. polymorpha to avoid confounding factors, particularly when investigating environmental effects on molecular regulation in the gonads, and to a lesser extent in the digestive glands.

Weight of evidence for cross-species conservation of androgen receptor-based biological activity

The U.S. Environmental Protection Agency's Endocrine Disruptor Screening Program (EDSP) is tasked with assessing chemicals for their potential to perturb endocrine pathways, including those controlled by androgen receptor (AR). To address challenges associated with traditional testing strategies, EDSP is considering in vitro high-throughput screening assays to screen and prioritize chemicals more efficiently. The ability of these assays to accurately reflect chemical interactions in nonmammalian species remains uncertain. Therefore, a goal of the EDSP is to evaluate how broadly results can be extrapolated across taxa. To assess the cross-species conservation of AR-modulated pathways, computational analyses and systematic literature review approaches were used to conduct a comprehensive analysis of existing in silico, in vitro, and in vivo data. First, molecular target conservation was assessed across 585 diverse species based on the structural similarity of ARs. These results indicate that ARs are conserved across vertebrates and are predicted to share similarly susceptibility to chemicals that interact with the human AR. Systematic analysis of over 5000 published manuscripts was used to compile in vitro and in vivo cross-species toxicity data. Assessment of in vitro data indicates conservation of responses occurs across vertebrate ARs, with potential differences in sensitivity. Similarly, in vivo data indicate strong conservation of the AR signaling pathways across vertebrate species, although sensitivity may vary. Overall, this study demonstrates a framework for utilizing bioinformatics and existing data to build weight of evidence for cross-species extrapolation and provides a technical basis for extrapolating hAR-based data to prioritize hazard in nonmammalian vertebrate species.

Exploring the mechanisms underlying the toxicity of boric acid against the land snail, Theba pisana

BACKGROUND

The land snail, Theba pisana, is one of the most important threats facing agriculture around the globe. Boric acid (BOA) is currently used as a safe alternative molluscicide to control land snails in sustainable agriculture, but the mechanisms of toxicity have not yet been investigated. The present study characterizes the lethal and sub-lethal (0.5 and 1 mg g^-1 ) toxic effects of BOA-contaminated food for 14 days by examining physiological, biochemical and histopathological indicators in T. pisana to understand the mechanisms underlying its toxic action.

RESULTS

BOA was found to be lethal against T. pisana with LC₅₀ values of 24.7 and 8.05 mg g^-1 after 3 and 7 days of exposure, respectively. BOA sublethal concentrations led to a significant reduction in food consumption and growth of snails after 14 days of exposure. BOA also caused a significant increase in testosterone levels, whereas an opposite effect was observed in estradiol levels. An increase in progesterone levels in snails in the 0.5 mg g^-1 BOA group and a decrease in the 1 mg g^-1 BOA group were observed after all exposure times. Moreover, the lipid peroxidation level and catalase activity were elevated, whereas acetylcholinesterase activity was inhibited in the treated snails. Alteration in glutathione-S-transferase activity was noticed after exposure to both sublethal concentrations. In addition, BOA induced histopathological alterations in the digestive gland of T. pisana.

CONCLUSION

Our findings provide novel insights into how physiological, biochemical and histopathological alterations can be used to explore the mechanisms underlying BOA toxicity against snails. © 2022 Society of Chemical Industry.

Expression and functional analyses for estrogen receptor and estrogen related receptor of Yesso scallop, Patinopecten yessoensis

Estrogen receptors (ERs) were known as estrogen-activated transcription factors and function as major reproduction regulators in vertebrates. The presence of er genes had been reported in Molluscan cephalopods and gastropods. However, they were considered as constitutive activators with unknown biological functions since reporter assays for these ERs did not show a specific response to estrogens. In this study, we tried characterization of ER orthologues from the Yesso scallop, Patinopecten yessoensis, in which estrogens had been proven to be produced in the gonads and involved in the spermatogenesis and vitellogenesis. Identified ER and estrogen related receptor (ERR) of Yesso scallops, designated as py-ER and py-ERR, conserved specific domain structures for a nuclear receptor. Their DNA binding domains showed high similarities to those of vertebrate ER orthologues, while ligand binding domains had low similarities with them. Both the py-er and py-err expression levels decreased in the ovary at the mature stage while py-vitellogenin expression increased in the ovary by quantitative real-time RT-PCR. Also, the py-er and py-err showed higher expressions in the testis than ovary during the developing and mature period, suggesting both genes might function in the spermatogenesis and testis development. The py-ER showed binding affinities to vertebrate estradiol-17β (E₂). However, the intensity was weaker than the vertebrate ER, indicating scallops might exist endogenous estrogens with a different structure. On the other hand, the binding property of py-ERR to E₂ was not confirmed in this assay, speculating that py-ERR was a constitutive activator as other vertebrate ERRs. Further, the py-er was localized in the spermatogonia in the testis and in the auxiliary cells in the ovary by in situ hybridization, indicating its potential roles in promoting spermatogenesis and vitellogenesis. Taken together, the present study demonstrated that py-ER was an authentic E₂ receptor in the Yesso scallop and might have functions for the spermatogonia proliferation and vitellogenesis, while py-ERR was involved in the reproduction by undiscovered manners.

Stage-Specific Transcriptomes of the Mussel Mytilus coruscus Reveals the Developmental Program for the Planktonic to Benthic Transition

Many marine invertebrate larvae undergo complex morphological and physiological changes during the planktonic-benthic transition (a.k.a. metamorphosis). In this study, transcriptome analysis of different developmental stages was used to uncover the molecular mechanisms underpinning larval settlement and metamorphosis of the mussel, Mytilus coruscus. Analysis of highly upregulated differentially expressed genes (DEGs) at the pediveliger stage revealed enrichment of immune-related genes. The results may indicate that larvae co-opt molecules of the immune system to sense and respond to external chemical cues and neuroendocrine signaling pathways forecast and trigger the response. The upregulation of adhesive protein genes linked to byssal thread secretion indicates the anchoring capacity required for larval settlement arises prior to metamorphosis. The results of gene expression support a role for the immune and neuroendocrine systems in mussel metamorphosis and provide the basis for future studies to disentangle gene networks and the biology of this important lifecycle transformation.

Sex steroid profile during oocyte development and maturation in the intertidal worm Marphysa madrasi (Polychaeta: Eunicidae) from the east coast of India

Marphysa madrasi is a commercially valuable maturation diet in crustacean aquaculture. This study presents the first detailed investigation of oogenesis in the intertidal polychaete worm M. madrasi and reports the steroid profile during oocyte growth and development. Oogenesis is extraovarian type I, originating from coelomic epithelial cells, with four stages of development - primary growth, early vitellogenic, late vitellogenic, and maturation. The primary growth phase contains oogonial cells and previtellogenic oocyte clusters in the early, mid, and late stages of development form a dispersed ovary attached to blood vessels. The late previtellogenic oocytes detach from the ovary at the onset of vitellogenesis. The detached oocytes complete vitellogenesis and final maturation in the coelomic fluid as solitary free-floating cells without any connection with follicle cells. The worms display asynchronous reproduction with a heterogeneous population of developing oocytes. Steroid extracts from the polychaete homogenates in different stages of oogenesis were identified by HPLC and confirmed by LC-MS/MS. In M. madrasi, two vertebrate-type steroids, pregnenolone (P5) and 17α-hydroxyprogesterone (17-OHP) were detected and quantified. The P5 levels were low in immature worms but increased significantly by ∼ 8.3-fold in the previtellogenic stage and peaked during oocyte maturation. 17-OHP levels were low in immature worms but gradually increase as the oogenesis progress to the primary growth and early vitellogenic phase, with a significant increase (p < 0.001) during the late vitellogenic phase. Although an increase in the concentration of P5 and 17-OHP during vitellogenesis and maturation of oocytes points to a possible role in reproduction, the absence of other vertebrate-type steroids in the investigated polychaete signifies a plausible uptake of P5 and 17-OHP from the environment.

Common aquatic pollutants modify hemocyte immune responses in Biomphalaria glabrata

Disruptions to reproductive health in wildlife species inhabiting polluted environments is often found to occur alongside compromised immunity. However, research on impacts of aquatic pollution on freshwater mollusc immune responses is limited despite their importance as vectors of disease (Schistosomiasis) in humans, cattle and wild mammals. We developed an in vitro 'tool-kit' of well-characterized quantitative immune tests using Biomphalaria glabrata hemocytes. We exposed hemocytes to environmentally-relevant concentrations of common aquatic pollutants (17β-estradiol, Bisphenol-A and p,p'-DDE) and measured key innate immune responses including motility, phagocytosis and encapsulation. Additionally, we tested an extract of a typical domestic tertiary treated effluent as representative of a 'real-world' mixture of chemicals. Encapsulation responses were stimulated by p,p'-DDE at low doses but were suppressed at higher doses. Concentrations of BPA (above 200 ng/L) and p,p'-DDE (above 500 ng/L) significantly inhibited phagocytosis compared to controls, whilst hemocyte motility was reduced by all test chemicals and the effluent extract in a dose-dependent manner. All responses occurred at chemical concentrations considered to be below the cytotoxic thresholds of hemocytes. This is the first time a suite of in vitro tests has been developed specifically in B. glabrata with the purpose of investigating the impacts of chemical pollutants and an effluent extract on immunity. Our findings indicate that common aquatic pollutants alter innate immune responses in B. glabrata, suggesting that pollutants may be a critical, yet overlooked, factor impacting disease by modulating the dynamics of parasite transmission between molluscs and humans.

The ecotoxicology of marine tributyltin (TBT) hotspots: A review

Tributyltin (TBT) was widely used as a highly efficient biocide in antifouling paints for ship and boat hulls. Eventually, TBT containing paints became globally banned when TBT was found to cause widespread contamination and non-target adverse effects in sensitive species, with induced pseudohermaphroditism in female neogastropods (imposex) being the best-known example. In this review, we address the history and the status of knowledge regarding TBT pollution and marine TBT hotspots, with a special emphasis on the Norwegian coastline. The review also presents a brief update on knowledge of TBT toxicity in various marine species and humans, highlighting the current understanding of toxicity mechanisms relevant for causing endocrine disruption in marine species. Despite observations of reduced TBT sediment concentrations in many marine sediments over the recent decades, contaminant hotspots are still prevalent worldwide. Consequently, efforts to monitor TBT levels and assessment of potential effects in sentinel species being potentially susceptible to TBT in these locations are still highly warranted.

Development of transient trapping micellar electrokinetic chromatography coupled with mass spectrometry for steroids analysis

An on-line sample preconcentration technique based on transient trapping (tr-trapping) in micellar electrokinetic chromatography (MEKC) was applied for steroid detection with UV (tr-trapping-UV) and electrospray ionization mass spectrometry detection (tr-trapping-ESI-MS). ESI-MS was used to improve the sensitivity in MEKC. The MEKC separation was carried out using volatile ammonium formate as a background solution to facilitate the coupling with ESI-MS. The partial introduction of a sodium dodecyl sulfate (SDS) micellar solution before the introduction of a sample solution to the capillary provided the effective preconcentration of analytes. At the same time, the SDS micelle would not enter the ESI-MS system, so its interference in ESI-MS detection was suppressed under the optimal condition, then five steroids can be separated by the developed method. In tr-trapping-ESI-MS, an acidic condition of pH 3.5 was employed to suppress the electroosmotic flow, which can avoid micellar solution migrating to the MS instrument. The developed method showed that the micellar solution requires a twofold slower time than the sample to migrate along the column, which can prohibit the cause of the problem with the MS instrument and interference signal of SDS in the steroid's detection. The tr-trapping-ESI-MS protocol showed up to 540-fold enhancements of the peak intensity and 50-fold improvement of the limit of detection compared with capillary zone electrophoresis using androsterone as a model sample.

Studies on a widely-recognized snail model species (Lymnaea stagnalis) provide further evidence that vertebrate steroids do not have a hormonal role in the reproduction of mollusks

Experiments were carried out to determine whether, as with other mollusks that have been studied, the snail, Lymnaea stagnalis, can absorb, esterify and store vertebrate steroids that are present in the water. We also carried out experiments to determine whether neural tissues of the snail could be immunohistochemically stained with an antibody to human aromatase (a key enzyme that catalyzes the conversion of testosterone [T] to 17β-estradiol [E₂]); and, if so, to determine the significance of such staining. Previous studies on other mollusks have reported such staining and have proposed this as decisive evidence that mollusks have the same steroid synthesis pathway as vertebrates. We found that snails absorb, esterify and retain esterified T, E₂, progesterone and ethinyl-estradiol (albeit with an absorption rate about four times slower, on a weight basis, than the mussel, Mytilus edulis). We also found that not only anti-human aromatase, but also anti-human nuclear progesterone receptor (nPR) and anti-human gonadotropin-releasing hormone antibodies immunohistochemically stained snail neural cells. However, further experiments, involving gel electrophoretic separation, followed by immunostaining, of proteins extracted from the neural tissue, found at least two positively-stained bands for each antibody, none of which had masses matching the human proteins to which the antibodies had been raised. The anti-aromatase antibody even stained the 140 kDA ladder protein used as a molecular weight marker on the gels. Mass spectrometric analysis of the bands did not find any peptide sequences that corresponded to the human proteins. Our findings confirm that the presence of vertebrate-like sex steroids in molluscan tissues is not necessarily evidence of endogenous origin. The results also show that immunohistochemical studies using antibodies against human proteins are grossly non-specific and likely to have little or no value in studying steroid synthesis or activity in mollusks. Our conclusions are consistent with the fact that genes for aromatase and nPR have not been found in the genome of the snail or of any other mollusk. Our overarching conclusion, from this and our previous studies, is that the endocrinology of mollusks is not the same as that of humans or any other vertebrates and that continuing to carry out physiological and ecotoxicological studies on mollusks on the basis of this false assumption, is an unconscionable waste of resources.

Application of SNP in Genetic Sex Identification and Effect of Estradiol on Gene Expression of Sex-Related Genes in Strongylocentrotus intermedius

Sea urchin (Strongylocentrotus intermedius) is an economically important mariculture species in Asia, and its gonads are the only edible part. The efficiency of genetic breeding in sea urchins is hampered due to the inability to distinguish gender by appearance. In this study, we first identified a sex-associated single nucleotide polymorphism (SNP) by combining type IIB endonuclease restriction site-associated DNA sequencing (2b-RAD-seq) and genome survey. Importantly, this SNP is located within spata4, a gene specifically expressed in male. Knocking down of spata4 by RNA interference (RNAi) in male individuals led to the downregulation of other conserved testis differentiation-related genes and germ cell marker genes. We also revealed that sex ratio in this validated culture population of S. intermedius is not 1:1. Moreover, after a 58-day feeding experiment with estradiol, the expression levels of several conserved genes that are related to testis differentiation, ovary differentiation, and estrogen metabolism were dynamically changed. Taken together, our results will contribute toward improving breeding efficiency, developing sex-controlled breeding, and providing a solid base for understanding sex determination mechanisms in sea urchins.

The Uptake of Sporopollenin Exine Capsules and Associated Bioavailability of Adsorbed Oestradiol in Selected Aquatic Invertebrates

Lycopodium clavatum sporopollenin exine capsules (SpECs) are known to both adsorb and absorb chemicals. The aim of the present work was to determine whether oestradiol (E2) is 'bioavailable' to bioindicator species, either pre-adsorbed to, or in the presence of, SpECs. SpEC uptake was confirmed for Daphnia magna and Dreissena bugensis. E2 levels varied among treatments for Caenorhabditis elegans though there was no relationship to SpEC load. E2 was not detected in D. bugensis tissues. Expression changes of general stress and E2-specific genes were measured. For C. elegans, NHR-14 expression suggested that SpECs modulate E2 impacts, but not general health responses. For D. magna, SpECs alone and with E2 changed Vtg1 and general stress responses. For D. bugensis, SpECS were taken up but no E2 or change in gene expression was detected after exposure to E2 and/or SpECs. The present study is the first to investigate SpECs and bound chemical dynamics.

Progestogen-induced alterations and their ecological relevance in different embryonic and adult behaviours of an invertebrate model species, the great pond snail (Lymnaea stagnalis)

The presence of oral contraceptives (basically applying estrogens and/or progestogens) poses a challenge to animals living in aquatic ecosystems and reflects a rapidly growing concern worldwide. However, there is still a lack in knowledge about the behavioural effects induced by progestogens on the non-target species including molluscs. In the present study, environmental progestogen concentrations were summarised. Knowing this data, we exposed a well-established invertebrate model species, the great pond snail (Lymnaea stagnalis) to relevant equi-concentrations (1, 10, 100, and 500 ng L-1) of mixtures of four progestogens (progesterone, drospirenone, gestodene, levonorgestrel) for 21 days. Significant alterations were observed in the embryonic development time, heart rate, feeding, and gliding activities of the embryos as well as in the feeding and locomotion activity of the adult specimens. All of the mixtures accelerated the embryonic development time and the gliding activity. Furthermore, the 10, 100, and 500 ng L-1 mixtures increased the heart rate and feeding activity of the embryos. The 10, 100, and 500 ng L-1 mixtures affected the feeding activity as well as the 1, 10, and 100 ng L-1 mixtures influenced the locomotion of the adult specimens. The differences of these adult behaviours showed a biphasic response to the progestogen exposure; however, they changed approximately in the opposite way. In case of feeding activity, this dose-response phenomenon can be identified as a hormesis response. Based on the authors' best knowledge, this is the first study to investigate the non-reproductive effects of progestogens occurring also in the environment on molluscan species. Our findings contribute to the global understanding of the effects of human progestogens, as these potential disruptors can influence the behavioural activities of non-target aquatic species. Future research should aim to understand the potential mechanisms (e.g., receptors, signal pathways) of progestogens induced behavioural alterations.

Transcriptomics reveal triphenyltin-induced molecular toxicity in the marine mussel Perna viridis

Triphenyltin (TPT) is widely used as an active ingredient in antifouling paints and fungicides, and continuous release of this highly toxic endocrine disruptor has caused serious pollution to coastal marine ecosystems and organisms worldwide. Using bioassays and transcriptome sequencing, this study comprehensively investigated the molecular toxicity of TPT chloride (TPTCl) to the marine mussel Perna viridis which is a commercially important species and a common biomonitor for marine pollution in Southeast Asia. Our results indicated that TPTCl was highly toxic to adult P. viridis, with a 96-h LC₁₀ and a 96-h EC₁₀ at 18.7 μg/L and 2.7 μg/L, respectively. A 21-day chronic exposure to 2.7 μg/L TPTCl revealed a strong bioaccumulation of TPT in gills (up to 36.48 μg/g dry weight) and hepatopancreas (71.19 μg/g dry weight) of P. viridis. Transcriptome analysis indicated a time course dependent gene expression pattern in both gills and hepatopancreas. Higher numbers of differentially expressed genes were detected at Day 21 (gills: 1686 genes; hepatopancreas: 1450 genes) and at Day 28 (gills: 628 genes; hepatopancreas: 238 genes) when compared with that at Day 7 (gills: 104 genes, hepatopancreas: 112 genes). Exposure to TPT strongly impaired the endocrine system through targeting on nuclear receptors and putative steroid metabolic genes. Moreover, TPT widely disrupted cellular functions, including lipid metabolism, xenobiotic detoxification, immune response and endoplasmic-reticulum-associated degradation expression, which might have caused the bioaccumulation of TPT in the tissues and aggregation of peptides and proteins in cells that further activated the apoptosis process in P. viridis. Overall, this study has advanced our understanding on both ecotoxicity and molecular toxic mechanisms of TPT to marine mussels, and contributed empirical toxicity data for risk assessment and management of TPT contamination.

Modeling the metabolic profile of Mytilus edulis reveals molecular signatures linked to gonadal development, sex and environmental site

The monitoring of anthropogenic chemicals in the aquatic environment including their potential effects on aquatic organisms, is important for protecting life under water, a key sustainable development goal. In parallel with monitoring the concentrations of chemicals of concern, sentinel species are often used to investigate the biological effects of contaminants. Among these, bivalve molluscs such as mussels are filter-feeding and sessile, hence an excellent model system for measuring localized pollution. This study investigates the relationship between the metabolic state of the blue mussel (Mytilus edulis) and its physiology in different environments. We developed a computational model based on a reference site (relatively unpolluted) and integrated seasonal dynamics of metabolite relative concentrations with key physiological indicators and environmental parameters. The analysis of the model revealed that changes in metabolite levels during an annual cycle are influenced by water temperature and are linked to gonadal development. This work supports the importance of data-driven biology and its potential in environmental monitoring.

Function and Evolution of Nuclear Receptors in Environmental-Dependent Postembryonic Development

Nuclear receptors (NRs) fulfill key roles in the coordination of postembryonal developmental transitions in animal species. They control the metamorphosis and sexual maturation in virtually all animals and by that the two main environmental-dependent developmental decision points. Sexual maturation and metamorphosis are controlled by steroid receptors and thyroid receptors, respectively in vertebrates, while both processes are orchestrated by the ecdysone receptor (EcR) in insects. The regulation of these processes depends on environmental factors like nutrition, temperature, or photoperiods and by that NRs form evolutionary conserved mediators of phenotypic plasticity. While the mechanism of action for metamorphosis and sexual maturation are well studied in model organisms, the evolution of these systems is not entirely understood and requires further investigation. We here review the current knowledge of NR involvement in metamorphosis and sexual maturation across the animal tree of life with special attention to environmental integration and evolution of the signaling mechanism. Furthermore, we compare commonalities and differences of the different signaling systems. Finally, we identify key gaps in our knowledge of NR evolution, which, if sufficiently investigated, would lead to an importantly improved understanding of the evolution of complex signaling systems, the evolution of life history decision points, and, ultimately, speciation events in the metazoan kingdom.

Vitellogenin gene expression in marine mussels exposed to ethinylestradiol: No induction at the transcriptional level

Vitellogenin (Vtg), a large multidomain protein precursor of egg-yolk proteins, is used as an endocrine disruption biomarker in fish, and in the last decades, its use has been extended to invertebrates like mollusks. However, it remains unclear whether invertebrate endocrine system produces Vtg in response to estrogens, like it occurs in oviparous vertebrates. In a previous study, no evidence of induction of Vtg expression at protein level was found in gonads of the marine mussel Mytilus galloprovincialis after exposure to the estrogenic chemical 17α-ethinylestradiol (EE2). In the present follow-up study, it was investigated whether there is any effect of EE2 on Vtg abundance at transcriptional level in M. galloprovincialis gonads. To this aim, RT-qPCR analysis targeting three different domains of Vtg transcript was performed on gonads of mussels that were exposed either 4 or 24 days to 100 ng/L EE2. In addition, several reference genes were analysed and a selection of these for potential use in further RT-qPCR analyses on mussel male and female gonads is provided. Results showed higher expression in females than in males for the three analysed Vtg domains, and no evidence of Vtg mRNA induction due to EE2 either in females or males. The present results, together with those obtained from previous analysis at protein level, support that Vtg is not an adequate biomarker for xenoestrogenicity in marine mussels. Additionally, nucleotide sequences of Vtg transcripts of three closely-related species from Mytilus edulis complex (M. galloprovincialis, M. edulis and M. trossulus) are provided and compared with Vtg sequences from other mollusk species to assess the level of conservation and evolutionary relationships among species.

Ocean acidification but not hypoxia alters the gonad performance in the thick shell mussel Mytilus coruscus

Ocean acidification and hypoxia have become increasingly severe in coastal areas, and their co-occurrence poses emerging threats to coastal ecosystems. Here, we investigated the combined effects of ocean acidification and hypoxia on the reproductive capacity of the thick-shelled mussel Mytilus coruscus. Our results demonstrated low pH but not low oxygen induced decreased gonadosomatic index (GSI) in mussels. Male mussels had a lower level of sex steroids (estradiol, testosterone, and progesterone) when kept at low pH. Expression of genes related to reproduction were also impacted by low pH with a downregulation of genes involved in gonad development in males (β-catenin and Wnt-7b involved in males) and an upregulation of testosterone synthesis inhibition-related gene (Wnt-4) in females. Overall, our results suggest that ocean acidification has an impact on the gonadal development through an alternation of gene expression and level of steroids while hypoxia had no significant effect.

Exposure to estrogenic mixtures results in tissue-specific alterations to the metabolome of oysters

The current study investigated the effect of environmentally relevant mixtures of estrogens at levels representative of receiving waters on the metabolome of the Sydney rock oyster, Saccostrea glomerata. Oysters were exposed to a "low" and a "high" mixture of (xeno) estrogens (representative of Australian and global receiving waters respectively) for 7 days and digestive gland, gill, and gonad tissue were sampled for quantification of polar metabolites by ¹H NMR spectroscopy. Exposure to both mixtures lowered body mass and altered the metabolite profile in the digestive glands. Comparatively, gills, and ovaries demonstrated lesser sensitivity to the mixtures, with significant metabolomic alterations observed only for the high mixture. The male gonad did not respond to either estrogenic exposure. In the responsive tissues, major metabolites including amino acids, carbohydrates, intermediates of the tricarboxylic acid cycle and ATP were all down-regulated and exhibited tissue-specific patterns of down-regulation with the greatest proportion of metabolites down-regulated due to estrogenic exposure in the digestive gland. Exposure to (xeno) estrogen mixtures representative of concentrations reported in receiving waters in Australia and globally can impact the metabolome and associated energy metabolism, especially in the digestive gland, translating to lower pools of available ATP energy for potential cellular homeostasis, somatic maintenance and growth, reproduction and fitness.

Sex steroids and steroidogenesis-related genes in the sea cucumber, Holothuria scabra and their potential role in gonad maturation

The sea cucumber Holothuria scabra is an economically valuable marine species which is distributed throughout the Asia-Pacific region. With the natural population declining due to over fishing, aquaculture of this species is deemed necessary. Hence, it is essential to understand the mechanisms regulating the reproduction in order to increase their populations. Sex steroids, including estrogens, androgens and progestogens, play an important role in reproduction in most vertebrates and several invertebrates. It has been proposed that sea cucumbers have the same sex steroids as vertebrates but the steroidogenic pathway in the sea cucumbers is still unclear. In this study, we demonstrated by using liquid chromatography-tandem mass spectrometry (LC-MS/MS) that sex steroids (estradiol, progesterone, and testosterone) were present in H. scabra neural and gonadal tissues. In silico searches of available sea cucumber transcriptome data identified 26 steroidogenesis-related genes. Comparative analysis of encoded proteins for the steroidogenic acute regulatory protein (HscStAR), CYP P450 10, 17 and 3A (HscCYP10, HscCYP17, HscCYP3A) and hydroxysteroid dehydrogenases (Hsc3β-HSD, Hsc17β-HSD) with other species was performed to confirm their evolutionary conservation. Gene expression analyses revealed widespread tissue expression. Real-time PCR analysis revealed that HscStAR, HscCYP10, Hsc3β-HSD, and Hsc17β-HSD gene expressions were similar to those in ovaries and testes, which increased during the gonad maturation. HscCYP17 mRNA was increased during ovarian development and its expression declined at late stages in females but continued high level in males. The expression of the HscCYP3A was high at the early stages of ovarian development, but not at other later stages in ovaries, however it remained low in testes. Moreover, a role for steroids in reproduction was confirmed following the effect of sex steroids on vitellogenin (Vtg) expression in ovary explant culture, showing upregulation of Vtg level. Collectively, this study has confirmed the existence of steroids in an echinoderm, as well as characterizing key genes associated with the steroidogenic pathway. We propose that sex steroids might also be associated with the reproduction of H. scabra, and the identification of biosynthetic genes enables future functional studies to be performed.

Does estrogen regulate vitellogenin synthesis in corals?

Most broadcast spawner corals have a vitellogenic phase that lasts at least 6 months. It is established that estrogen regulates vitellogenin synthesis in vertebrates. Although some research have been conducted on the physiological role of sex steroids in corals, little is known about their involvement in oocyte development. This study aimed to detect steroid hormones - progesterone, testosterone, and estradiol-17β (E2) - in Acropora tenuis and study the relationships between vitellogenesis/vitellogenin synthesis and these steroids. This study also investigated the effect of E2 on vitellogenin synthesis in corals and identified steroidogenic enzymes in A. tenuis genome. Branches from tagged coral colonies were collected monthly from March to November. Histological observations showed that oocytes were vitellogenic from March to May (Stage IV and V), but not in June, and that gonads were occupied by immature oocytes in September (Stage I). Real-time qPCR revealed that vitellogenin (vg1 and vg2) transcript levels in coral branches were high in April and May, implying that corals actively underwent vitellogenesis during these months, and spawned before June. Liquid chromatography-mass spectrometry revealed that E2 could be detected in coral branches in March, April, and May, but not in June, whereas testosterone and progesterone did not fluctuate much in the same months. Immersing branches in E2-containing seawater failed to increase vitellogenin transcript levels. The results indicate that E2 is involved in oogenesis but does not positively regulate vitellogenin synthesis. Steroidogenic enzymes (except CYP19A) were identified in A. tenuis, suggesting that corals may endogenously synthesize progestogens and androgens from cholesterol.

Consecutive sexual maturation observed in a rock shell population in the vicinity of the Fukushima Daiichi Nuclear Power Plant, Japan

In 2012, after the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) that followed the Tohoku earthquake and tsunami in March 2011, no rock shell (Thais clavigera; currently recognized as Reishia clavigera; Gastropoda, Neogastropoda, Muricidae) specimens were found near the plant from Hirono to Futaba Beach (a distance of approximately 30 km). In July 2016, however, rock shells were again found to inhabit the area. From April 2017 to May 2019, we collected rock shell specimens monthly at two sites near the FDNPP (Okuma and Tomioka) and at a reference site ~ 120 km south of the FDNPP (Hiraiso). We examined the gonads of the specimens histologically to evaluate their reproductive cycle and sexual maturation. The gonads of the rock shells collected at Okuma, ~ 1 km south of the FDNPP, exhibited consecutive sexual maturation during the 2 years from April 2017 to May 2019, whereas sexual maturation of the gonads of specimens collected at Hiraiso was observed only in summer. The consecutive sexual maturation of the gonads of the specimens collected at Okuma might not represent a temporary phenomenon but rather a site-specific phenotype, possibly caused by specific environmental factors near the FDNPP.

The Uptake of Ethinyl-Estradiol and Cortisol From Water by Mussels (Mytilus spp.)

Previous toxicokinetic studies have shown that mussels (Mytilus spp.) can readily absorb the three main mammalian sex steroids, estradiol (E₂), testosterone (T) and progesterone (P) from water. They also have a strong ability to store E₂ and the 5α-reduced metabolites of T and P in the form of fatty acid esters. These esters were shown to have half-lives that were measured in weeks (i.e. they were not subject to fast depuration). The present study looked at the toxicokinetic profile of two other common steroids that are found in water, the potent synthetic oestrogen, (ethinyl-estradiol) (EE_2; one of the two components of 'the pill'), and cortisol, a natural stress steroid in vertebrates. In the first three hours of uptake, tritiated EE₂ was found to be taken up at a similar rate to tritiated E₂. However, the levels in the water plateaued sooner than E₂. The ability of the animals to both esterify and sulphate EE₂ was found to be much lower than E₂, but nevertheless did still take place. After 24 h of exposure, the majority of radiolabelled EE₂ in the animals was present in the form of free steroid, contrary to E_2, which was esterified. This metabolism was reflected in a much lower half-life (of only 15 h for EE₂ in the mussels as opposed to 8 days for E₂ and >10 days for T and P). Intriguingly, hardly any cortisol (in fact none at all in one of the experiments) was absorbed by the mussels. The implications of this finding in both toxicokinetic profiling and evolutionary significance (why cortisol might have evolved as a stress steroid in bony fishes) are discussed.

Toxicity of the pharmaceuticals finasteride and melengestrol acetate to benthic invertebrates

The toxicity of endocrinologically active pharmaceuticals finasteride (FIN) and melengestrol acetate (MGA) was assessed in freshwater mussels, including acute (48 h) aqueous tests with glochidia from Lampsilis siliquoidea, sub-chronic (14 days) sediment tests with gravid female Lampsilis fasciola, and chronic (28 days) sediment tests with juvenile L. siliquoidea, and in chronic (42 days) sediment tests with the amphipod Hyalella azteca and the mayfly Hexagenia spp. Finasteride was not toxic in acute aqueous tests with L. siliquoidea glochidia (up to 23 mg/L), whereas significant toxicity to survival and burial ability was detected in chronic sediment tests with juvenile L. siliquoidea (chronic value (ChV, the geometric mean of LOEC and NOEC) = 58 mg/kg (1 mg/L)). Amphipods (survival, growth, reproduction, and sex ratio) and mayflies (growth) were similarly sensitive (ChV = 58 mg/kg (1 mg/L)). Melengestrol acetate was acutely toxic to L. siliquoidea glochidia at 4 mg/L in aqueous tests; in sediment tests, mayflies were the most sensitive species, with significant growth effects observed at 37 mg/kg (0.25 mg/L) (ChV = 21 mg/kg (0.1 mg/L)). Exposure to sublethal concentrations of FIN and MGA had no effect on the (luring and filtering) behaviour of gravid L. fasciola, or the viability of their brooding glochidia. Based on the limited number of measured environmental concentrations of both chemicals, and their projected concentrations, no direct effects are expected by these compounds individually on the invertebrates tested. However, organisms are exposed to contaminant mixtures in the aquatic environment, and thus, the effects of FIN and MGA as components of these mixtures require further investigation.

A critical evaluation of some of the recent so-called 'evidence' for the involvement of vertebrate-type sex steroids in the reproduction of mollusks

Many studies on the control of reproduction in mollusks have focused on hormones (and proteins associated with the production and signaling of those hormones) which were originally discovered in humans, in the belief that if they are also present in mollusks, they must have the same role. However, although human sex steroids can be found in mollusks, they are so readily absorbed that their presence is not necessarily evidence of endogenous synthesis. A homolog of the vertebrate nuclear estrogen receptor has been found in mollusks, but it does not bind to estrogens or indeed to any steroid at all. Antibodies against human aromatase show positive immunostaining in mollusks, yet the aromatase gene has not been found in the genome of any invertebrates (let alone mollusks). This review will deal with these and other examples of contradictory evidence for a role of human hormones in invertebrate reproduction.

The unlimited potential of the great pond snail, Lymnaea stagnalis

Only a limited number of animal species lend themselves to becoming model organisms in multiple biological disciplines: one of these is the great pond snail, Lymnaea stagnalis. Extensively used since the 1970s to study fundamental mechanisms in neurobiology, the value of this freshwater snail has been also recognised in fields as diverse as host-parasite interactions, ecotoxicology, evolution, genome editing and 'omics', and human disease modelling. While there is knowledge about the natural history of this species, what is currently lacking is an integration of findings from the laboratory and the field. With this in mind, this article aims to summarise the applicability of L. stagnalis and points out that this multipurpose model organism is an excellent, contemporary choice for addressing a large range of different biological questions, problems and phenomena.

No evidence that vitellogenin protein expression is induced in marine mussels after exposure to an estrogenic chemical

A wide variety of endocrine disrupting chemicals reach the marine environment and can cause harmful effects in different marine organisms. Vitellogenin (Vtg), the egg-yolk precursor, is a commonly used endocrine disruption biomarker in fish and more recently in marine invertebrates under the assumption of high expected similarities in the endocrine system of vertebrates and invertebrates. However, this assumption has been recently questioned. The results from previous studies focused on bivalve molluscs showed that Vtg induction could be misleading because of the use of either non-robust or indirect techniques to measure Vtg. In this study, mussels (Mytilus galloprovincialis) were exposed to either 10 or 100 ng/L of the synthetic hormone 17α-ethinylestradiol (EE2) at different exposure times (4 and 24 days) and under different feeding regimes (representing different energy balances), and Vtg levels in both male and female mussel gonads were quantified by label free shotgun LC-MS/MS proteomic analysis. Vtg protein was not detected in male gonads. In female gonads, Vtg levels were not significantly affected by EE2 at any exposure time or EE2 concentration tested, whereas a significant correlation was found between the degree of maturation of the gonad and Vtg levels in females. Results obtained in the present study critically question the use of Vtg as a biomarker of endocrine disruption in marine mussels, and show that the degree of maturation of the gonad can be an important confounding factor in the attempts to evaluate estrogenic effects through Vtg measurement in mussel gonads.

Concentrations levels and effects of 17alpha-Ethinylestradiol in freshwater and marine waters and bivalves: A review

Pharmaceutical drugs are contaminants of emerging concern and are amongst the most frequent in the aquatic environment. Even though a vast literature indicate that pharmaceuticals exert negative impacts towards aquatic organisms, mainly in vertebrates, there is still limited information regarding the effects of these drugs in freshwater and marine bivalves. Marine bivalves have a high ecological and socio-economic value and are considered good bioindicator species in ecotoxicology and risk assessment programs. Furthermore, another lacking point on these studies is the absence of bioconcentration data, with no clear relationship between the concentration of drugs on tissue and the biological effects. 17alpha-ethinylestradiol (EE2) is a synthetic hormone with high estrogenic potency that was added to the Watch List adopted by the European Commission stating the priority substances to be monitored. Thus, this review summarizes the current knowledge on the concentration levels and effects of EE2 on freshwater and marine bivalves. The inclusion in the Watch List, the presence in freshwater and marine systems, and the impact exerted on aquatic biota, even at trace concentrations, justify the review devoted to this pharmaceutical drug. Globally the available studies found that EE2 induces individual and sub-individual (e.g. tissue, cellular, biochemical and molecular levels of biological organization) impacts in bivalves. Essentially, this estrogenic compound, even in trace concentrations, was found to have accumulated in wild and laboratory exposed bivalves. The most common effects reported were changes on the reproductive function and energy metabolism. The studies used in this review support keeping the EE2 on the Watch List and highlight the need to increase the number of monitorization studies since clear negative effects were exerted on bivalves by this drug.

Antineoplastic Agents: Environmental Prevalence and Adverse Outcomes in Aquatic Organisms

Cancer is the second leading cause of death worldwide, with 9.6 million cancer-related deaths in 2018. Cancer incidence has increased over time, and so has the prescription rate of chemotherapeutic drugs. These pharmaceuticals, known as antineoplastic agents, enter the aquatic environment via human excretion and wastewater. The objectives of the present critical review were to investigate the risk of antineoplastics to aquatic species and to summarize the current state of knowledge regarding their levels in the environment, because many antineoplastics are not adequately removed during wastewater treatment. We conducted 2 separate literature reviews to synthesize data on the global environmental prevalence and toxicity of antineoplastics. The antineoplastics most frequently detected in the environment included cyclophosphamide, ifosfamide, tamoxifen, methotrexate, and 5-fluorouracil; all were detectable in multiple water sources, including effluent and surface waters. These antineoplastics span 3 different mechanistic classes, with cyclophosphamide and ifosfamide classified as alkylating agents, tamoxifen as a hormonal agent, and methotrexate and 5-fluorouracil as antimetabolites. Studies that characterize the risk of antineoplastics released into aquatic environments are scarce. We summarize the biological impacts of the most environmentally prevalent antineoplastics on aquatic organisms and propose an adverse outcome pathway for cyclophosphamide and ifosfamide, 2 widely prescribed drugs with a similar immunotoxic mode of action. Acute and chronic ecotoxicity studies using aquatic models are needed for risk characterization of antineoplastics. Environ Toxicol Chem 2020;39:967-985. © 2020 SETAC.

Effect of gonadotropin releasing hormone on the expression of luteinizing hormone and estrogen in the nerve ganglia and ovary of a tropical abalone, Haliotis asinina Linnaeus

Gonadotropin releasing hormone (GnRH) is a peptide brain hormone that is involved in the regulation of reproduction in vertebrates via stimulation of the secretion of the pituitary hormones, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which in their turn stimulate sexual development and sex steroid hormone secretion by the gonads. The tropical abalone, Haliotis asinina, in common with many other invertebrates contains a peptide with a similar structure to GnRH. This study looks at its possible involvement in reproduction by injecting groups of one-year-old female abalone at the mature phase by injecting them with synthetic H. asinina (Has) GnRH at doses of 0, 250 and 500 ng/g and then measuring the amount of material in nerve ganglia, ovary and hemolymph that cross-reacted with enzyme-linked immunosorbent assays (ELISA) for vertebrate LH and steroid, estradiol. Immunohistochemistry, using antibodies for the same two compounds, was also carried out to examine the location of immunoactivity in the tissues of the animals. There were slight (in some cases statistically significant) increases in LH-immunoactivity and estradiol in the hemolymph and tissues. However, this applied to the lower dose only (i.e the dose-response relationship was non-monotonic). Using immunohistochemistry, LH-immunoreactive cells were observed in types 1 and 2 neurosecretory (NS1 and NS2) cells within the cerebral and pleuropedal ganglia of H. asinina. In addition, LH-immunoreactive nerve fiber bundles were strongly detected in both ganglia. The immunoactivity against the estrogen appeared to be localized in the granulated cells within the connective tissue and trabeculae of the mature ovary. There was no positive staining in the cytoplasm of any stage of the germ cells. The interpretation of these findings is presently hindered by the fact that the homologous gene for vertebrate LH has not yet been identified in the genomes of any mollusks (so the cause of the immunostaining is as yet unknown) and also by the fact that mollusks are known to readily absorb steroids from the environment and store them long-term in the form of fatty acid esters. More work, involving identification of the protein that cross-reacts with the LH antiserum and also exclusion of the possibility that the estradiol is of exogenous origin, will have to be carried out before these findings can be used to manipulate reproduction in this species.

Early embryonic exposure of freshwater gastropods to pharmaceutical 5-alpha-reductase inhibitors results in a surprising open-coiled "banana-shaped" shell

In vertebrates, the steroidogenesis enzyme 5α-reductase converts testosterone to the more potent androgen 5α-dihydrotestosterone. Homologues of 5α-reductase genes have been identified in molluscs. However, recent findings suggest that vertebrate-type steroid androgens are not utilised in molluscan reproductive development. Genomic searches have revealed that molluscs do not possess many of the steroidogenic enzymes required to make testosterone, nor a nuclear androgen receptor. Consequently, the role of 5α-reductase in molluscs presents a mystery. Here, developmental exposures of Biomphalaria glabrata to selective pharmaceutical 5α-reductase inhibitors elicited a strong, highly reproducible phenotypic response characterised by the development of elongated "banana-shaped" shell morphology. In comparison to untreated snails, the shells are open-coiled and the whorls are unattached. Dutasteride (5α-reductase inhibitor) is approximately 10-times more potent at provoking the banana-shaped shell phenotype than finasteride, paralleling the pharmaceuticals' efficacy in humans. Other enzyme inhibitors with different modes of action were tested to investigate the specificity of the phenotype. However, only the pharmaceutical 5α-reductase inhibitors provoked the response. Dutasteride elicited the same phenotype in a second gastropod, Physella acuta. In the absence of evidence for de novo androgen steroidogenesis in molluscs, these findings suggest that novel substrates for 5α-reductase exist in gastropods, lending support to the contention that molluscan endocrinology differs from the well-characterised vertebrate endocrine system.

Estrogenic compounds as exogenous modulators of physiological functions in molluscs: Signaling pathways and biological responses

Molluscs have been widely utilized to evaluate the effects of estrogenic compounds, one of the most widespread classes of Endocrine Disrupting Chemicals-EDCs. However, knowledge on steroid signaling and metabolism in molluscs has considerably increased in the last decade: from these studies, a considerable debate emerged on the role of 'natural' steroids in physiology, in particular in reproduction, of this invertebrate group. In this work, available information on the effects and mechanisms of action of estrogens in molluscs will be reviewed, with particular emphasis on bivalves that, widespread in aquatic ecosystems, are most likely affected by exposure to estrogenic EDCs. Recent advances in steroid uptake and metabolism, and estrogen receptors-ERs in molluscs, as well as in estrogen signaling in vertebrates, will be considered. The results so far obtained with 17β-estradiol and different estrogenic compounds in the model bivalve Mytilus spp., demonstrate specific effects on immune function, development and metabolism. Transcriptomic data reveal non genomic estrogen signaling pathways in mussel tissues that are supported by new observations at the cellular level. In vitro and in vivo data show, through independent lines of evidence, that estrogens act through non-genomic signaling pathways in bivalves. In this light, regardless of whether molluscs synthesize estrogens de novo or not, and despite their ERs are not directly activated by ligand binding, estrogens can interact with multiple signaling components, leading to modulation of different physiological functions. Increasing knowledge in endocrine physiology of molluscs will provide a framework for a better evaluation and interpretation of data on the impact of estrogenic EDCs in this invertebrate group.

Steroids originating from bacterial bile acid degradation affect Caenorhabditis elegans and indicate potential risks for the fauna of manured soils

Bile acids are steroid compounds from the digestive tracts of vertebrates that enter agricultural environments in unusual high amounts with manure. Bacteria degrading bile acids can readily be isolated from soils and waters including agricultural areas. Under laboratory conditions, these bacteria transiently release steroid compounds as degradation intermediates into the environment. These compounds include androstadienediones (ADDs), which are C₁₉-steroids with potential hormonal effects. Experiments with Caenorhabditis elegans showed that ADDs derived from bacterial bile acid degradation had effects on its tactile response, reproduction rate, and developmental speed. Additional experiments with a deletion mutant as well as transcriptomic analyses indicated that these effects might be conveyed by the putative testosterone receptor NHR-69. Soil microcosms showed that the natural microflora of agricultural soil is readily induced for bile acid degradation accompanied by the transient release of steroid intermediates. Establishment of a model system with a Pseudomonas strain and C. elegans in sand microcosms indicated transient release of ADDs during the course of bile acid degradation and negative effects on the reproduction rate of the nematode. This proof-of-principle study points at bacterial degradation of manure-derived bile acids as a potential and so-far overlooked risk for invertebrates in agricultural soils.

Genomic sequence analyses of classical and non-classical lamprey progesterone receptor genes and the inference of homologous gene evolution in metazoans

BACKGROUND

Nuclear progesterone receptor (nPR) is an evolutionary innovation in vertebrates that mediates genomic responses to progesterone. Vertebrates also respond to progesterone via membrane progesterone receptors (mPRs) or membrane associated progesterone receptors (MAPRs) through rapid nongenomic mechanisms. Lampreys are extant agnathan vertebrates, residing at the evolutionary juncture where vertebrates diverged from invertebrates. A survey of the progesterone receptor (PR) gene sequences in lamprey genomes would inform PR gene evolutionary events during the transition from invertebrates to vertebrates.

RESULTS

In this study, we annotated sequences of one nPR, four mPR (β, γ, δ and ε) and four MAPR genes from genomes of two lamprey species (Petromyzon marinus and Lethenteron japonicum). To infer the origin and evolutionary history of PR genes, we constructed phylogenetic trees of PR homologous sequences across representative species of metazoans. Phylogenetic analyses revealed that the mPRγ gene first appeared in non-bilaterians, and the mPRβ gene likely arose from a duplication of mPRγ. On the other hand, the mPRγ gene gave rise to the mPRδ and ε genes much later in the vertebrate lineage. In addition, the mPRα gene first appeared in cartilaginous fishes, likely derived from duplication of mPRβ after the agnathan-gnathostome divergence. All known MAPR genes were present in the lamprey genomes. Progesterone receptor membrane component 1 (PGRMC1), neudesin and neuferricin genes probably evolved in parallel in non-bilaterians, whereas two copies of PGRMC genes probably derived from duplication of ancestral PGRMC1 sequence and appeared before the speciation of lampreys.

CONCLUSIONS

Non-classical mPR and MAPR genes first evolved in non-bilaterians and classical nPR genes evolved later in basal vertebrates. Sequence repertoires for membrane progesterone receptor genes in vertebrates likely originated from an ancestral metazoan sequence and expanded via several duplication events.

Aromatisation of steroids in the bivalve Mytilus trossulus

In this study, we demonstrated the presence of the enzymatic complex able to perform aromatization (estrogen synthesis) in both, the microsomal and mitochondrial fractions of gills and gonads from Mytilus trossulus. Based on in vitro experiments, we highlighted the importance of temperature as the limiting factor of aromatisation efficiency (AE) in mussels. After testing range of temperatures (4–23 °C), the highest AE was found during incubation at 8 °C and pH 7.6 (41.66 pmol/h/mg protein in gills and 58.37 pmol/h/mg protein in gonads). The results were confirmed during field studies where the most efficient aromatisation occurred in bivalves collected in spring while the least effective in those collected in winter. During in vitro studies, AE turned out to be more intensive in female gonads than in male gonads. The process was also more intensive in mitochondrial fraction than in microsomal one (62.97 pmol/h/mg protein in male gills and 73.94 pmol/h/mg protein in female gonads). Enzymatic complex (aromatase-like enzyme) catalysing aromatisation in mussels was found to be insensitive to inhibitory effect of selective inhibitors of mammalian aromatase such as letrozole and anastrazole, suggesting its different structure from vertebrate aromatase. Further in vivo studies using ¹³C-labeled steroids at 8 °C temperature window confirmed that bivalves are able to uptake testosterone and androstenedione from the ambient environment and metabolise them to estrone and 17β-estradiol thus confirming endogenous estrogen’ synthesis.

Scientific integrity issues in Environmental Toxicology and Chemistry: Improving research reproducibility, credibility, and transparency

High-profile reports of detrimental scientific practices leading to retractions in the scientific literature contribute to lack of trust in scientific experts. Although the bulk of these have been in the literature of other disciplines, environmental toxicology and chemistry are not free from problems. While we believe that egregious misconduct such as fraud, fabrication of data, or plagiarism is rare, scientific integrity is much broader than the absence of misconduct. We are more concerned with more commonly encountered and nuanced issues such as poor reliability and bias. We review a range of topics including conflicts of interests, competing interests, some particularly challenging situations, reproducibility, bias, and other attributes of ecotoxicological studies that enhance or detract from scientific credibility. Our vision of scientific integrity encourages a self-correcting culture that promotes scientific rigor, relevant reproducible research, transparency in competing interests, methods and results, and education. Integr Environ Assess Manag 2019;00:000-000. © 2019 SETAC.

The utility of vitellogenin as a biomarker of estrogenic endocrine disrupting chemicals in molluscs

Estrogenic endocrine disrupting chemicals (EDCs) are natural hormones, synthetic compounds or industrial chemicals that mimic estrogens due to their structural similarity with estrogen's functional moieties. They typically enter aquatic environments through wastewater treatment plant effluents or runoff from intensive livestock operations. Globally, most natural and synthetic estrogens in receiving aquatic environments are in the low ng/L range, while industrial chemicals (such as bisphenol A, nonylphenol and octylphenol) are present in the μg to low mg/L range. These environmental concentrations often exceed laboratory-based predicted no effect concentrations (PNECs) and have been evidenced to cause negative reproductive impacts on resident aquatic biota. In vertebrates, such as fish, a well-established indicator of estrogen-mediated endocrine disruption is overexpression of the egg yolk protein precursor vitellogenin (Vtg) in males. Although the vertebrate Vtg has high sensitivity and specificity to estrogens, and the molecular basis of its estrogen inducibility has been well studied, there is growing ethical concern over the use of vertebrate animals for contaminant monitoring. The potential utility of the invertebrate Vtg as a biomonitor for environmental estrogens has therefore gained increasing attention. Here we review evidence providing support that the molluscan Vtg holds promise as an invertebrate biomarker for exposure to estrogens. Unlike vertebrates, estrogen signalling in invertebrates remains largely unclarified and the classical genomic pathway only partially explains estrogen-mediated activation of Vtg. In light of this, in the latter part of this review, we summarise recent progress towards understanding the molecular mechanisms underlying the activation of the molluscan Vtg gene by estrogens and present a hypothetical model of the interplay between genomic and non-genomic pathways in the transcriptional regulation of the gene.

Effects on tadpole snail gene expression after exposure to vinclozolin

The fungicide vinclozolin (Vz) is an endocrine disruptor with known anti-androgenic activity in vertebrates. However, there is a lack of information about the Vz mode of action in invertebrates, although some studies have shown that this compound can produce alterations in different species. Transcriptional activity was analyzed in the freshwater snail Physella acuta in order to elucidate putative cellular processes altered by this chemical during a response. In order to identify potential molecular biomarkers, a de novo transcriptome was generated for this species that constitutes a valuable source for future studies. This data, together with some already available data, permitted the identification of several genes related to detoxification mechanisms (Cyp2u1, Cyp3a7, Cyp4f22, GSTo1, GSTt2, and MRP1), stress response (Hsp20.4, Hsp17, Hsp16.6, and Cu,Zn-SOD), the hormonal system (Estrogen Receptor and Hsp90), apoptosis (Casp3), and copper homeostasis (ATOX1). Using quantitative Real-Time polymerase chain reaction, mRNA levels of these genes were examined in snails exposed to 20 or 200 µg/L Vz for 24 h. The results showed an overall weak response, with downregulation of Hsp20.4 and no statistically significant change for the other genes. These findings suggest that P. acuta can manage the concentrations of Vz found in the environment with no relevant activation of the pathways analyzed, although additional studies are needed for longer exposure times and including other metabolic pathways. The new genes described open the range of processes that can be studied at the molecular level in toxicity tests.