Molecular cloning, characterisation and molecular modelling of two novel T-synthases from mollusc origin

The glycoprotein-N-acetylgalactosamine β1,3-galactosyltransferase, known as T-synthase (EC 2.4.1.122), plays a crucial role in the synthesis of the T-antigen, which is the core 1 O-glycan structure. This enzyme transfers galactose from UDP-Gal to GalNAc-Ser/Thr. The T-antigen has significant functions in animal development, immune response, and recognition processes. Molluscs are a successful group of animals that inhabit various environments, such as freshwater, marine, and terrestrial habitats. They serve important roles in ecosystems as filter feeders and decomposers but can also be pests in agriculture and intermediate hosts for human and cattle parasites. The identification and characterization of novel carbohydrate active enzymes, such as T-synthase, can aid in the understanding of molluscan glycosylation abilities and their adaptation and survival abilities. Here, the T-synthase enzymes from the snail Pomacea canaliculata and the oyster Crassostrea gigas are identified, cloned, expressed, and characterized, with a focus on structural elucidation. The synthesized enzymes display core 1 β1,3-galactosyltransferase activity using pNP-α-GalNAc as substrate and exhibit similar biochemical parameters as previously characterised T-synthases from other species. While the enzyme from C. gigas shares the same structural parameters with the other enzymes characterised so far, the T-synthase from P. canaliculata lacks the consensus sequence CCSD, which was previously considered indispensable.

Hemoglobin wonders: a fascinating gas transporter dive into molluscs

Hemoglobin (Hb) has been identified in at least 14 molluscan taxa so far. Research spanning over 130 years on molluscan Hbs focuses on their genes, protein structures, functions, and evolution. Molluscan Hbs are categorized into single-, two-, and multiple-domain chains, including red blood cell, gill, and extracellular Hbs, based on the number of globin domains and their respective locations. These Hbs exhibit variation in assembly, ranging from monomeric and dimeric to higher-order multimeric forms. Typically, molluscan Hbs display moderately high oxygen affinity, weak cooperativity, and varying pH sensitivity. Hb's potential role in antimicrobial pathways could augment the immune defense of bivalves, which may be a complement to their lack of adaptive immunity. The role of Hb as a respiratory protein in bivalves likely originated from the substitution of hemocyanin. Molluscan Hbs demonstrate adaptive evolution in response to environmental changes via various strategies (e.g. increasing Hb types, multimerization, and amino acid residue substitutions at key sites), enhancing or altering functional properties for habitat adaptation. Concurrently, an increase in Hb assembly diversity, coupled with a downward trend in oxygen affinity, is observed during molluscan differentiation and evolution. Hb in Protobranchia, Heteroconchia, and Pteriomorphia bivalves originated from separate ancestors, with Protobranchia inheriting a relative ancient molluscan Hb gene. In bivalves, extracellular Hbs share a common origin, while gill Hbs likely emerged from convergent evolution. In summary, research on molluscan Hbs offers valuable insights into the origins, biological variations, and adaptive evolution of animal Hbs.

Molluscan Genomes Reveal Extensive Differences in Photopigment Evolution Across the Phylum

In animals, opsins and cryptochromes are major protein families that transduce light signals when bound to light-absorbing chromophores. Opsins are involved in various light-dependent processes, like vision, and have been co-opted for light-independent sensory modalities. Cryptochromes are important photoreceptors in animals, generally regulating circadian rhythm, they belong to a larger protein family with photolyases, which repair UV-induced DNA damage. Mollusks are great animals to explore questions about light sensing as eyes have evolved multiple times across, and within, taxonomic classes. We used molluscan genome assemblies from 80 species to predict protein sequences and examine gene family evolution using phylogenetic approaches. We found extensive opsin family expansion and contraction, particularly in bivalve xenopsins and gastropod Go-opsins, while other opsins, like retinochrome, rarely duplicate. Bivalve and gastropod lineages exhibit fluctuations in opsin repertoire, with cephalopods having the fewest number of opsins and loss of at least 2 major opsin types. Interestingly, opsin expansions are not limited to eyed species, and the highest opsin content was seen in eyeless bivalves. The dynamic nature of opsin evolution is quite contrary to the general lack of diversification in mollusk cryptochromes, though some taxa, including cephalopods and terrestrial gastropods, have reduced repertoires of both protein families. We also found complete loss of opsins and cryptochromes in multiple, but not all, deep-sea species. These results help set the stage for connecting genomic changes, including opsin family expansion and contraction, with differences in environmental, and biological features across Mollusca.

Unraveling the protective role of Nrf2 in molluscs: Insights into mitochondrial and apoptosis pathways in the defense against Bap-induced oxidative stress

Benzopyrene (Bap) is a major constituent of petroleum pollutants commonly found in aquatic environments, and its mutagenic and carcinogenic properties have adverse effects on aquatic organisms' development, growth, and reproduction. The antioxidant defense system element, NF-E2-related factor 2 (Nrf2), has been linked to the oxidative stress response in marine invertebrates exposed to toxic substances. In a previous study, a novel Nrf2 homologue, McNrf2, was identified in mussel Mytilus coruscus, a significant model marine molluscs in ecotoxicology studies. McNrf2 showed the potential to trigger an antioxidant defense against oxidative stress induced by Bap. Here, we employed an Nrf2 overexpression and inhibition model using SFN and ML385 as Nrf2 inducer and inhibitor, respectively. Next, immunofluorescence technique was used to evaluate the nuclear activation of Nrf2 induced by Bap-mediated oxidative stress. Transmission electron microscopy revealed that overexpression of Nrf2 could maintain the quantity and structural integrity of mitochondria, while flow cytometry analysis showed that Nrf2 could alleviate Bap-induced cellular apoptosis. These findings suggest that Nrf2 can protect molluscs from Bap-induced oxidative stress through the mitochondria and apoptosis pathways, providing a novel perspective on Nrf2's antioxidant function.

Identification, Characterization, and Expression of a β-Galactosidase from Arion Species (Mollusca)

β-Galactosidases (β-Gal, EC 3.2.1.23) catalyze the cleavage of terminal non-reducing β-D-galactose residues or transglycosylation reactions yielding galacto-oligosaccharides. In this study, we present the isolation and characterization of a β-galactosidase from Arion lusitanicus, and based on this, the cloning and expression of a putative β-galactosidase from Arion vulgaris (A0A0B7AQJ9) in Sf9 cells. The entire gene codes for a protein consisting of 661 amino acids, comprising a putative signal peptide and an active domain. Specificity studies show exo- and endo-cleavage activity for galactose β1,4-linkages. Both enzymes, the recombinant from A. vulgaris and the native from A. lusitanicus, display similar biochemical parameters. Both β-galactosidases are most active in acidic environments ranging from pH 3.5 to 4.5, and do not depend on metal ions. The ideal reaction temperature is 50 °C. Long-term storage is possible up to +4 °C for the A. vulgaris enzyme, and up to +20 °C for the A. lusitanicus enzyme. This is the first report of the expression and characterization of a mollusk exoglycosidase.

Dietary consumption of polypropylene microplastics alter the biochemical parameters and histological response in freshwater benthic mollusc Pomacea paludosa

One of the most common environmental pollutant in aquatic ecosystems are polypropylene microplastics and their impacts on aquatic organisms are still scarce. The study aimed to prepare polypropylene microplastics using organic solvent (spherical and 11.86-44.62 μm) and then test their toxicity on the freshwater benthic mollusc grazer Pomaceae paludosa. The present study investigated chronic (28 days) exposure of polypropylene microplastics via dietary supplements (250 mg kg^-1, 500 mg kg^-1 & 750 mg kg^-1) in P. paludosa, and the toxic effect was evaluated in digestive gland tissue. The FTIR results revealed no change in polypropylene microplastics during ingestion or after egestion. On the other hand, Ingestion causes accumulation in their bodies and disrupts redox homeostasis. Meanwhile, alteration occurs in oxidative stress-related biomarkers such as increased reactive oxygen species level (ROS), impaired the biochemical parameters of antioxidant system catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH), and glutathione - S- transferase (GST), deterioration of oxidative stress effects in lipid peroxidation (LPO) and carbonyl protein (CP) and changed the digestive enzymes such as amylase, pepsin, esterase and alkaline phosphatase that are measured in hepatopancreas tissue. The histology results revealed that ingesting these microplastics caused severe damage to the digestive gland cells. According to the findings, ingestion of polypropylene microplastics in benthic freshwater mollusc causes more serious harm and impacts energy acquisition. This finding represents the ecological risk of polypropylene microplastic pollution in the freshwater ecosystem.

Functional Characterization, Antimicrobial Effects, and Potential Antibacterial Mechanisms of NpHM4, a Derived Peptide of Nautilus pompilius Hemocyanin

Hemocyanins present in the hemolymph of invertebrates are multifunctional proteins that are responsible for oxygen transport and play crucial roles in the immune system. They have also been identified as a source of antimicrobial peptides during infection in mollusks. Hemocyanin has also been identified in the cephalopod ancestor Nautilus, but antimicrobial peptides derived from the hemocyanin of Nautilus pompilius have not been reported. Here, the bactericidal activity of six predicted peptides from N. pompilius hemocyanin and seven mutant peptides was analyzed. Among those peptides, a mutant peptide with 15 amino acids (1RVFAGFLRHGIKRSR15), NpHM4, showed relatively high antibacterial activity. NpHM4 was determined to have typical antimicrobial peptide characteristics, including a positive charge (+5.25) and a high hydrophobic residue ratio (40%), and it was predicted to form an alpha-helical structure. In addition, NpHM4 exhibited significant antibacterial activity against Gram-negative bacteria (MBC = 30 μM for Vibrio alginolyticus), with no cytotoxicity to mammalian cells even at a high concentration of 180 µM. Upon contact with V. alginolyticus cells, we confirmed that the bactericidal activity of NpHM4 was coupled with membrane permeabilization, which was further confirmed via ultrastructural images using a scanning electron microscope. Therefore, our study provides a rationalization for the development and optimization of antimicrobial peptide from the cephalopod ancestor Nautilus, paving the way for future novel AMP development with broad applications.

Multiple tachykinins and their receptors characterized in the gastropod mollusk Pacific abalone: Expression, signaling cascades, and potential role in regulating lipid metabolism

Tachykinin (TK) families, including the first neuropeptide substance P, have been intensively explored in bilaterians. Knowledge of signaling of TK receptors (TKRs) has enabled the comprehension of diverse physiological processes. However, TK signaling systems are largely unknown in Lophotrochozoa. This study identified two TK precursors and two TKR isoforms in the Pacific abalone Haliotis discus hannai (Hdh), and characterized Hdh-TK signaling. Hdh-TK peptides harbored protostomian TK-specific FXGXRamide or unique YXGXRamide motifs at the C-termini. A phylogenetic analysis showed that lophotrochozoan TKRs, including Hdh-TKRs, form a monophyletic group distinct from arthropod TKRs and natalisin receptor groups. Although reporter assays demonstrated that all examined Hdh-TK peptides activate intracellular cAMP accumulation and Ca²⁺ mobilization in Hdh-TKR-expressing mammalian cells, Hdh-TK peptides with N-terminal aromatic residues and C-terminal FXGXRamide motifs were more active than shorter or less aromatic Hdh-TK peptides with a C-terminal YXGXRamide. In addition, we showed that ligand-stimulated Hdh-TKRs mediate ERK1/2 phosphorylation in HEK293 cells and that ERK1/2 phosphorylation is inhibited by PKA and PKC inhibitors. In three-dimensional in silico Hdh-TKR binding modeling, higher docking scores of Hdh-TK peptides were consistent with the lower EC50 values in the reporter assays. The transcripts for Hdh-TK precursors and Hdh-TKR were highly expressed in the neural ganglia, with lower expression levels in peripheral tissues. When abalone were starved for 3 weeks, Hdh-TK1 transcript levels, but not Hdh-TK2, were increased in the cerebral ganglia (CG), intestine, and hepatopancreas, contrasting with the decreased lipid content and transcript levels of sterol regulatory element-binding protein (SREBP). At 24 h post-injection in vivo, the lower dose of Hdh-TK1 mixture increased SREBP transcript levels in the CG and hepatopancreas and accumulative food consumption of abalone. Higher doses of Hdh-TK1 and Hdh-TK2 mixtures decreased the SREBP levels in the CG. When Hdh-TK2-specific siRNA was injected into abalone, intestinal SREBP levels were significantly increased, whereas administration of both Hdh-TK1 and Hdh-TK2 siRNA led to decreased SREBP expression in the CG. Collectively, our results demonstrate the first TK signaling system in gastropod mollusks and suggest a possible role for TK peptides in regulating lipid metabolism in the neural and peripheral tissues of abalone.

Shifted mineral ions transport in the mollusk Unio pictorum exposed to environmental concentrations of diclofenac

Previous studies showed that diclofenac (DCF), when released in the environment, can be toxic to aquatic animals (fish and mollusks), affecting gills, which are the main organ of ionic regulation. This study focuses on detecting the effects of relevant environmental concentrations of DCF (0.1-1 μg L^-1) on the transport of main mineral cations, i.e. sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg), by widely distributed freshwater bivalve mollusks Unio pictorum. After 96-h exposure to river aerated water at 25 °C with DCF concentrations of 0 (control), 0.1 (treatment I), and 1 μg L^-1 (treatment II), the mollusks were transferred to deionized water, and daily (for 7 days) concentrations of these cations in the medium have been measured. Animals exposed to 1 μg L^-1 DCF maintained the ionic balance between the organism and the diluted medium at a significantly higher level of Na, K, and Mg ions in water compared to the control and animals exposed to 0.1 μg L^-1 DCF. At 0.1 μg L^-1 DCF, the greater loss concerning the control (p < 0.05) was found only for Na ion. There were no differences in the dynamics of Ca ions between control and both treatments. This study showed that detectable environmental concentrations of DCF in natural waters can influence the transport of main cations required by freshwater animals to maintain their ionic balance, and the observed effect (elevated ion loss) is ion-specific and also dose-dependent.

Morphology and organization of the internal shell of Ariolimax californicus (Gastropoda; Stylommatophora), an asymmetric two-face biomineralized matrix

A slug is a shell-less terrestrial gastropod mollusk. During evolution, slugs have lost their mineralized external shell but some of them have retained an internal shell (IS). Unlike external shells, which have been widely investigated, the ISs have been poorly studied. We report for the first time the compositional and complete morphological characterization of Ariolimax californicus' IS. According to literature, this shell calcifies and decalcifies depending on the animal's needs. Its composition is mostly organic, consisting of proteins and β-chitin. The internal shell is organized in layers and membranes in which CaCO₃ crystal formation occurs in specific areas. In the two faces of the IS we observed different morphologies and aggregations of calcite bio-crystals along with a different organization of the organic matrix. Dorsally, the mineral forms a thick layer composed of misaligned crystal aggregates of large dimensions, separated by thin organic layers. This suggests a protective purpose and the use of this layer as a long-term calcium storage system. Ventrally, the mineral phase is organized in small crystal aggregates of comparable size, separated by thin organic layers, and quite aligned one to the other. The whole ventral mineral layer is covered by a membrane, identified as the hypostracum. This face is proposed to be a short-term calcium storage system. In vitro crystallization experiments suggest massive calcium ions sequestration from the solution for the precipitation of calcite crystals inside the organic matrix. In conclusion, this research provides new information on the dynamic of biomineralization on mollusk evolved in calcium-poor environments.

The Enigmatic Metallothioneins: A Case of Upward-Looking Research

In the mid-1950s, Bert Lester Vallee and his colleague Marvin Margoshes discovered a molecule referred to today as metallothionein (MT). Meanwhile, MTs have been shown to be common in many biological organisms. Despite their prevalence, however, it remains unclear to date what exactly MTs do and how they contribute to the biological function of an organism or organ. We investigate why biochemical research has not yet been able to pinpoint the function(s) of MTs. We shall systematically examine both the discovery of and recent research on Dr. Vallee's beloved family of MT proteins utilizing tools from philosophy of science. Our analysis highlights that Vallee's initial work exhibited features prototypical of a developing research tradition: it was upward-looking, exploratory, and utilized mere interactions. Since the 1960s, MT research has increasingly become intervention- and hypothesis-based while it remained largely upward-looking in character. Whilst there is no reason to think that upward-looking research cannot successfully yield structure-function mappings, it has not yet been successful in the case of MTs. Thus, we suggest it might be time to change track and consider other research strategies looking into the evolution of MTs. Recent studies in mollusks render research in this direction worthy of pursuit.

The primitive interferon-like system and its antiviral function in molluscs

The phylum mollusca is a very important group in the animal kingdom for the large number and diversified species. Recently, interest in molluscan immunity has increased due to their phylogenetic position and importance in worldwide aquaculture and aquatic environment. As the main aquaculture animal, most molluscs live in the water environment and they have to cope with many pathogen challenges, in which virus is one of the primary causes for the mass mortality. In vertebrates, interferon (IFN) system is generally recognized as the first line of defence against viral infection, while the antiviral mechanisms in molluscs remain to be clearly illuminated. Recently, some IFN-like proteins and IFN-related components have been characterized from molluscs, such as pattern recognition receptors (PRRs), interferon regulatory factors (IRFs), IFN-like receptors, JAK/STAT and IFN-stimulated genes (ISGs), which reinforce the existence of IFN-like system in molluscs. This system can be activated by virus or poly (I:C) challenges and further regulate the antiviral response of haemocytes in molluscs. This review summarizes the research progresses of IFN-like system in molluscs with the emphases on the uniformity and heterogeneity of IFN-like system of molluscs compared to that of other animals, which will be helpful for elucidating the antiviral modulation in molluscs and understanding the origin and evolution of IFN system.

Anti-HBV Activities of Polysaccharides from Thais clavigera (Küster) by In Vitro and In Vivo Study

Hepatitis B virus (HBV) infection remains a major global health problem. It is therefore imperative to develop drugs for anti-hepatitis B with high-efficiency and low toxicity. Attracted by the observations and evidence that the symptoms of some patients from the Southern Fujian, China, suffering from hepatitis B were alleviated after daily eating an edible marine mollusk, Thais clavigera (Küster 1860) (TCK). Water-soluble polysaccharide from TCK (TCKP1) was isolated and characterized. The anti-HBV activity of TCKP1 and its regulatory pathway were investigated on both HepG2.2.15 cell line and HBV transgenic mice. The data obtained from in vitro studies showed that TCKP1 significantly enhanced the production of IFN-α, and reduced the level of HBV antigens and HBV DNA in the supernatants of HepG2.2.15 cells in a dose-dependent manner with low cytotoxicity. The result of the study on the HBV transgenic mice further revealed that TCKP1 significantly decreased the level of transaminases, HBsAg, HBeAg, and HBV DNA in the serum, as well as HBsAg, HBeAg, HBV DNA, and HBV RNA in the liver of HBV transgenic (HBV-Tg) mice. Furthermore, TCKP1 exhibited equivalent inhibitory effect with the positive control tenofovir alafenamide (TAF) on the markers above except for HBV DNA even in low dosage in a mouse model. However, the TCKP1 high-dose group displayed stronger inhibition of transaminases and liver HBsAg, HBeAg, and HBV RNA when compared with those of TAF. Meanwhile, inflammation of the liver was, by pathological observation, relieved in a dose-dependent manner after being treated with TCKP1. In addition, elevated levels of interleukin-12 (IL-12) and interferon γ (IFN-γ), and reduced level of interleukin-4 (IL-4) in the serum were observed, indicating that the anti-HBV effect of TCKP1 was achieved by potentiating immunocyte function and regulating the balance of Th1/Th2 cytokines.

Shellfish Toxin Uptake and Depuration in Multiple Atlantic Canadian Molluscan Species: Application to Selection of Sentinel Species in Monitoring Programs

Shellfish toxin monitoring programs often use mussels as the sentinel species to represent risk in other bivalve shellfish species. Studies have examined accumulation and depuration rates in various species, but little information is available to compare multiple species from the same harvest area. A 2-year research project was performed to validate the use of mussels as the sentinel species to represent other relevant eastern Canadian shellfish species (clams, scallops, and oysters). Samples were collected simultaneously from Deadmans Harbour, NB, and were tested for paralytic shellfish toxins (PSTs) and amnesic shellfish toxin (AST). Phytoplankton was also monitored at this site. Scallops accumulated PSTs and AST sooner, at higher concentrations, and retained toxins longer than mussels. Data from monitoring program samples in Mahone Bay, NS, are presented as a real-world validation of findings. Simultaneous sampling of mussels and scallops showed significant differences between shellfish toxin results in these species. These data suggest more consideration should be given to situations where multiple species are present, especially scallops.

The Iron-Responsive Genome of the Chiton Acanthopleura granulata

Molluscs biomineralize structures that vary in composition, form, and function, prompting questions about the genetic mechanisms responsible for their production and the evolution of these mechanisms. Chitons (Mollusca, Polyplacophora) are a promising system for studies of biomineralization because they build a range of calcified structures including shell plates and spine- or scale-like sclerites. Chitons also harden the calcified teeth of their rasp-like radula with a coat of iron (as magnetite). Here we present the genome of the West Indian fuzzy chiton Acanthopleura granulata, the first from any aculiferan mollusc. The A. granulata genome contains homologs of many genes associated with biomineralization in conchiferan molluscs. We expected chitons to lack genes previously identified from pathways conchiferans use to make biominerals like calcite and nacre because chitons do not use these materials in their shells. Surprisingly, the A. granulata genome has homologs of many of these genes, suggesting that the ancestral mollusc may have had a more diverse biomineralization toolkit than expected. The A. granulata genome has features that may be specialized for iron biomineralization, including a higher proportion of genes regulated directly by iron than other molluscs. A. granulata also produces two isoforms of soma-like ferritin: one is regulated by iron and similar in sequence to the soma-like ferritins of other molluscs, and the other is constitutively translated and is not found in other molluscs. The A. granulata genome is a resource for future studies of molluscan evolution and biomineralization.

Sterol Composition of Sponges, Cnidarians, Arthropods, Mollusks, and Echinoderms from the Deep Northwest Atlantic: A Comparison with Shallow Coastal Gulf of Mexico

Triterpenoid biosynthesis is generally anaerobic in bacteria and aerobic in Eukarya. The major class of triterpenoids in bacteria, the hopanoids, is different to that in Eukarya, the lanostanoids, and their 4,4,14-demethylated derivatives, sterols. In the deep sea, the prokaryotic contribution to primary productivity has been suggested to be higher because local environmental conditions prevent classic photosynthetic processes from occurring. Sterols have been used as trophic biomarkers because primary producers have different compositions, and they are incorporated in primary consumer tissues. In the present study, we inferred food supply to deep sea, sponges, cnidarians, mollusks, crustaceans, and echinoderms from euphotic zone production which is driven by phytoplankton eukaryotic autotrophy. Sterol composition was obtained by gas chromatography and mass spectrometry. Moreover, we compared the sterol composition of three phyla (i.e., Porifera, Cnidaria, and Echinodermata) collected between a deep and cold-water region and a shallow tropical area. We hypothesized that the sterol composition of shallow tropical benthic organisms would better reflect their photoautotrophic sources independently of the taxonomy. Shallow tropical sponges and cnidarians from environments showed plant and zooxanthellae sterols in their tissues, while their deep-sea counterparts showed phytoplankton and zooplankton sterols. In contrast, echinoids, a class of echinoderms, the most complex phylum along with hemichordates and chordates (deuterostomes), did not show significant differences in their sterol profile, suggesting that cholesterol synthesis is present in deuterostomes other than chordates.

Mechanism and Function of the Catch State in Molluscan Smooth Muscle: A Historical Perspective

Molluscan smooth muscles exhibit the catch state, in which both tension and resistance to stretch are maintained with very low rates of energy consumption. The catch state is studied mainly on the anterior byssus retractor muscle (ABRM) of a bivalve molluscan animal, Mytilus, which can easily be split into small bundles consisting of parallel fibers. The ABRM contracts actively with an increase in the intracellular free Ca ion concentration, [Ca²⁺]i, as with all other types of muscle. Meanwhile, the catch state is established after the reduction of [Ca²⁺]i to the resting level. Despite extensive studies, the mechanism underlying the catch state is not yet fully understood. This article briefly deals with (1) anatomical and ultrastructural aspects of the ABRM, (2) mechanical studies on the transition from the active to the catch state in the isotonic condition, (3) electron microscopic and histochemical studies on the intracellular translocation of Ca ions during the transition from the active to the catch state, and (4) biochemical studies on the catch state, with special reference to a high molecular mass protein, twitchin, which is known to occur in molluscan catch muscles.

Biochemical Responses of the Bivalve Mollusk Unio tumidus Inhabiting a Small Power Plant Reservoir on the Dniester River Basin, Ukraine

Hydropower plants (HPPs) can affect the hydrological regime. However, biochemical responses of aquatic animals for the evaluation of this disturbing are not applied yet. The specimens of Unio tumidus were sampled in a reservoir (R) of a small HPP as well as downstream from the dam (DS). Biochemical indexes in the digestive gland and alkali labile phosphates (ALP) in the gonads were examined. The R-mollusks showed low cholinesterase, catalase and caspase-3 activities, and metallothionein concentration, but elevated levels of zinc and copper, oxidized glutathione and protein carbonyls. Concentrations of lactate, pyruvate and ALP, activity of superoxide dismutase and glutathione S-transferase, and lipid peroxidation level were similar in both groups. Integrated biomarker response (IBR/n) index (n = 13) was 2.17 and 0.29 in the R- and DS-groups correspondingly. We suggest that using integrative biological response based on the biochemical markers of bivalve mollusks can be a valid early warning step in assessing 'environmental flow' impact.

Trace Elements in Crustaceans, Mollusks and Fish in the Kenyan Part of Lake Victoria: Bioaccumulation, Bioindication and Health Risk Analysis

This is the first comprehensive report on the accumulation of Cr, Ni, As, and Ag in the fish species Nile tilapia Oreochromis niloticus and Nile perch Lates niloticus from Lake Victoria, complemented with recent data on Cu, Zn, Cd, and Pb. This also is the first report on Cr, Ni, As, and Ag levels in invertebrates: the shrimp Caridina nilotica, gastropod Pila ovata, and bivalve Mutela bourguignati. The study was conducted at five sites in the Kenyan part of Lake Victoria: four sites in Winam Gulf influenced by various anthropogenic pressures, including a site near Kisumu City, and one in the main lake, with lesser direct anthropogenic influence. Apart from Cu and Ag, which were highest in O. niloticus liver, the invertebrates had higher levels of trace elements than fish. Contamination of the gulf with trace elements was best mirrored by the invertebrates, whose mobility is limited; they accumulated Cr, Cd, Ag, and Pb corresponding to the levels in the surface sediment. The accumulation of trace elements in fish species and their bioindicative potential corresponded to their habitats and feeding behaviour. The tissue contents of most trace elements were higher in the inshore-dwelling, omnivorous O. niloticus compared to the pelagic, piscivorous L. niloticus. Cu (465 ± 689 mg/kg dw) and Ag (3.45 ± 1.49 mg/kg dw) in the liver of O. niloticus were up to 10 and 119 times higher than in L. niloticus, respectively. Oreochromis niloticus therefore has bioindicative potential for Cu and Ag contamination. Both the invertebrates and fish showed positive correlations between Cu and Ag concentrations, indicating similar source and/or uptake route. The target hazard quotients (THQ) show that there is no human health risk associated with the consumption of these fish. However, the levels of Zn, Cd, and Pb in P. ovata surpassed maximum food safety limits and are hence potentially unsafe for human consumption.

Near-future ocean warming and acidification alter foraging behaviour, locomotion, and metabolic rate in a keystone marine mollusc

Environmentally-induced changes in fitness are mediated by direct effects on physiology and behaviour, which are tightly linked. We investigated how predicted ocean warming (OW) and acidification (OA) affect key ecological behaviours (locomotion speed and foraging success) and metabolic rate of a keystone marine mollusc, the sea hare Stylocheilus striatus, a specialist grazer of the toxic cyanobacterium Lyngbya majuscula. We acclimated sea hares to OW and/or OA across three developmental stages (metamorphic, juvenile, and adult) or as adults only, and compare these to sea hares maintained under current-day conditions. Generally, locomotion speed and time to locate food were reduced ~1.5- to 2-fold when the stressors (OW or OA) were experienced in isolation, but reduced ~3-fold when combined. Decision-making was also severely altered, with correct foraging choice nearly 40% lower under combined stressors. Metabolic rate appeared to acclimate to the stressors in isolation, but was significantly elevated under combined stressors. Overall, sea hares that developed under OW and/or OA exhibited a less severe impact, indicating beneficial phenotypic plasticity. Reduced foraging success coupled with increased metabolic demands may impact fitness in this species and highlight potentially large ecological consequences under unabated OW and OA, namely in regulating toxic cyanobacteria blooms on coral reefs.

Fatty Acids of Marine Mollusks: Impact of Diet, Bacterial Symbiosis and Biosynthetic Potential

The n-3 and n-6 polyunsaturated fatty acid (PUFA) families are essential for important physiological processes. Their major source are marine ecosystems. The fatty acids (FAs) from phytoplankton, which are the primary producer of organic matter and PUFAs, are transferred into consumers via food webs. Mollusk FAs have attracted the attention of researchers that has been driven by their critical roles in aquatic ecology and their importance as sources of essential PUFAs. The main objective of this review is to focus on the most important factors and causes determining the biodiversity of the mollusk FAs, with an emphasis on the key relationship of these FAs with the food spectrum and trophic preference. The marker FAs of trophic sources are also of particular interest. The discovery of new symbioses involving invertebrates and bacteria, which are responsible for nutrition of the host, deserves special attention. The present paper also highlights recent research into the molecular and biochemical mechanisms of PUFA biosynthesis in marine mollusks. The biosynthetic capacities of marine mollusks require a well-grounded evaluation.

Untargeted metabolomic analysis of the carotenoid-based orange coloration in Haliotis gigantea using GC-TOF-MS

Seafood coloration is typically considered an indicator of quality and nutritional value by consumers. One such seafood is the Xishi abalone (Haliotis gigantea), which displays muscle color polymorphism wherein a small subset of individuals display orange coloration of muscles due to carotenoid enrichment. However, the metabolic basis for carotenoid accumulation has not been thoroughly investigated in marine mollusks. Here, GC-TOF-MS-based untargeted metabolite profiling was used to identify key pathways and metabolites involved in differential carotenoid accumulation in abalones with variable carotenoid contents. Cholesterol was the most statistically significant metabolite that differentiated abalones with orange muscles against those with common white muscles. This observation is likely due to the competitive interactions between cholesterol and carotenoids during cellular absorption. In addition, the accumulation of carotenoids was also related to fatty acid contents. Overall, this study indicates that metabolomics can reflect physiological changes in organisms and provides a useful framework for exploring the mechanisms underlying carotenoid accumulation in abalone types.

Biomineralization by particle attachment in early animals

Crystallization by particle attachment (CPA) of amorphous precursors has been demonstrated in modern biomineralized skeletons across a broad phylogenetic range of animals. Precisely the same precursors, hydrated (ACC-H2O) and anhydrous calcium carbonate (ACC), have been observed spectromicroscopically in echinoderms, mollusks, and cnidarians, phyla drawn from the 3 major clades of eumetazoans. Scanning electron microscopy (SEM) here also shows evidence of CPA in tunicate chordates. This is surprising, as species in these clades have no common ancestor that formed a mineralized skeleton and appear to have evolved carbonate biomineralization independently millions of years after their late Neoproterozoic divergence. Here we correlate the occurrence of CPA from ACC precursor particles with nanoparticulate fabric and then use the latter to investigate the antiquity of the former. SEM images of early biominerals from Ediacaran and Cambrian shelly fossils show that these early calcifiers used attachment of ACC particles to form their biominerals. The convergent evolution of biomineral CPA may have been dictated by the same thermodynamics and kinetics as we observe today.

Novel Genes, Ancient Genes, and Gene Co-Option Contributed to the Genetic Basis of the Radula, a Molluscan Innovation

The radula is the central foraging organ and apomorphy of the Mollusca. However, in contrast to other innovations, including the mollusk shell, genetic underpinnings of radula formation remain virtually unknown. Here, we present the first radula formative tissue transcriptome using the viviparous freshwater snail Tylomelania sarasinorum and compare it to foot tissue and the shell-building mantle of the same species. We combine differential expression, functional enrichment, and phylostratigraphic analyses to identify both specific and shared genetic underpinnings of the three tissues as well as their dominant functions and evolutionary origins. Gene expression of radula formative tissue is very distinct, but nevertheless more similar to mantle than to foot. Generally, the genetic bases of both radula and shell formation were shaped by novel orchestration of preexisting genes and continuous evolution of novel genes. A significantly increased proportion of radula-specific genes originated since the origin of stem-mollusks, indicating that novel genes were especially important for radula evolution. Genes with radula-specific expression in our study are frequently also expressed during the formation of other lophotrochozoan hard structures, like chaetae (hes1, arx), spicules (gbx), and shells of mollusks (gbx, heph) and brachiopods (heph), suggesting gene co-option for hard structure formation. Finally, a Lophotrochozoa-specific chitin synthase with a myosin motor domain (CS-MD), which is expressed during mollusk and brachiopod shell formation, had radula-specific expression in our study. CS-MD potentially facilitated the construction of complex chitinous structures and points at the potential of molecular novelties to promote the evolution of different morphological innovations.

The people behind the papers - Masanori Abe and Reiko Kuroda

One of the most obvious examples of left-right asymmetry in animal bodies comes from snails: in most species or strains, the shells coil dextrally, but some coil sinistrally. The control of coiling is genetic and begins in the early embryo. Previous work has implicated the formin diaphanous in the regulation of snail shell chirality, and a new paper in Development now decisively proves its involvement, thanks to the first application of CRISPR/Cas9 gene knockouts in molluscs. We caught up with the author team behind the paper: Masanori Abe and his supervisor Reiko Kuroda, Professor at Chubu University in Japan (recently moved from Tokyo University of Science), to find out more.

Occurrence and level of emerging organic contaminant in fish and mollusk from Klang River estuary, Malaysia and assessment on human health risk

The occurrence, level, and distribution of multiclass emerging organic contaminants (EOCs) in fish and mollusks from the Klang River estuary were examined. The targeted EOCs for this assessment were phenolic endocrine disrupting compounds (bisphenol A, 4-OP, and 4-NP), organophosphorous pesticides (quinalphos, chlorpyrifos, and diazinon), estrogenic hormones (E2, E1, and EE2), and pharmaceutically active chemicals (primidone, sulfamethoxazole, dexamethasone, diclofenac, amoxicillin, progesterone, and testosterone). Results from this study showed that the prevalent contamination of the Klang River estuary by EOCs with diclofenac, bisphenol A, progesterone, and amoxicillin were predominantly detected in fish and mollusks. Among the EOCs, diclofenac and progesterone had the highest concentrations in fish and mollusk samples, respectively. The concentrations of diclofenac and progesterone in fish and mollusk samples range from 1.42 ng/g to 10.76 ng/g and from 0.73 ng/g to 9.57 ng/g, respectively. Bisphenol A should also be highlighted because of its significant presence in both fish and mollusks. The concentration of bisphenol A in both matrices range from 0.92 ng/g to 5.79 ng/g. The calculated hazard quotient (HQ) for diclofenac, bisphenol A, and progesterone without consideration to their degradation byproduct were less than one, thus suggesting that the consumption of fish and mollusks from the Klang River estuary will unlikely pose any health risk to consumers on the basis of the current assessment. Nonetheless, this preliminary result is an important finding for pollution studies in Malaysian tropical coastal ecosystems, particularly for organic micropollutant EOCs, and can serve as a baseline database for future reference.

Polybrominated diphenyl ethers and alternative halogenated flame retardants in mollusks from the Chinese Bohai Sea: Levels and interspecific differences

Polybrominated diphenyl ethers (PBDEs) and alternative halogenated flame retardants (AHFRs) were measured in eleven mollusk species collected from the Chinese Bohai Sea. PBDEs and AHFRs were detected in all species, and their average total concentrations were in the range of 22.5-355 and 10.0-84.3 ng/g lipid weight, respectively. Decabromodiphenyl ether (BDE-209) and decabromodiphenylethane (DBDPE) were the dominant halogenated flame retardants (HFRs), contributing 22.5% to 73.6% and 3.1% to 38.3% of the total HFRs, respectively. The levels of PBDEs and AHFRs were moderate to high from a global perspective. Interspecific differences in the accumulation of PBDEs and AHFRs were characterized by heat map and cluster analysis. Composition profile differences were also observed, with higher proportions of AHFRs in gastropods than in bivalves. These species-specific differences in concentrations and profiles in mollusks were attributed to different species traits, including feeding habit, trophic level, and metabolic potential.

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.

A new bis-γ-pyrone polypropionate from a marine pulmonate mollusc Onchidium struma

A new bis-γ-pyrone polypropionate compound onchidione II (1), together with three known compounds, was isolated from a marine pulmonate mollusc Onchidium struma, collected at Hainan Island of China. The structure of new compound was determined by extensive spectroscopic analyses including IR, 1D and 2D NMR techniques, and chemical methods. Compounds 1-4 were evaluated for their cytotoxicity against human tumor cell lines HepG-2, A549, and MCF-2. The results showed that compounds 1 and 2 were moderate cytotoxic against HepG-2, A549, and MCF-2 cell lines, with IC₅₀ values from 13.2 to 22.4 μM.

Molecular assessment of wild populations in the marine realm: Importance of taxonomic, seasonal and habitat patterns in environmental monitoring

Scientists are currently faced with the challenge of assessing the effects of anthropogenic stressors on aquatic ecosystems. Cellular stress response (CSR) biomarkers are ubiquitous and phylogenetically conserved among metazoans and have been successfully applied in environmental monitoring but they can also vary according to natural biotic and abiotic factors. The reported variability may thus limit the wide application of biomarkers in monitoring, imposing the need to identify variability levels in the field. Our aim was to carry out a comprehensive in situ assessment of the CSR (heat shock protein 70 kDa, ubiquitin, antioxidant enzymes) and oxidative damage (lipid peroxidation) in wild populations across marine taxa by collecting fish, crustaceans, mollusks and cnidarians during two different seasons (spring and summer) and two habitat types (coast and estuary). CSR end-point patterns were different between taxa with mollusks having higher biomarker levels, followed by the cnidarians, while fish and crustaceans showed lower biomarker levels. The PCA showed clear clusters related to mobility/sessile traits with sessile organisms showing greater levels (>2-fold) of CSR proteins and oxidative damage. Mean intraspecific variability in the CSR measured by the coefficient of variation (% CV) (including data from all seasons and sites) was elevated (35-94%). Overall, there was a seasonal differentiation in biomarker patterns across taxonomic groups, especially evident in fish and cnidarians. A differentiation in biomarker patterns between habitat types was also observed and associated with phenotypic plasticity or local adaptation. Overall, specimens collected in the estuary had lower biomarker levels when compared to specimens collected in the coast. This work highlights the importance of assessing baseline biomarker levels across taxa, seasons and habitats prior to applying biomarker analyses in environmental monitoring. Selecting bioindicator species, defining sampling strategies, and identifying confounding factors are crucial preliminary steps that ensure the success of biomarkers as powerful tools in biomonitoring.

The retinoic acid receptor (RAR) in molluscs: Function, evolution and endocrine disruption insights

Retinoid acid receptor (RAR)-dependent signalling pathways are essential for the regulation and maintenance of essential biological functions and are recognized targets of disruptive anthropogenic compounds. Recent studies put forward the inability of mollusc RARs to bind and respond to the canonical vertebrate ligand, retinoic acid: a feature that seems to have been lost during evolution. Yet, these studies were carried out in a limited number of molluscs. Therefore, using an in vitro transactivation assay, the present work aimed to characterize phylogenetically relevant mollusc RARs, as monomers or as functional units with RXR, not only in the presence of vertebrate bone fine ligands but also known endocrine disruptors, described to modulate retinoid-dependent pathways. In general, none of the tested mollusc RARs were able to activate reporter gene transcription when exposed to retinoic acid isomers, suggesting that the ability to respond to retinoic acid was lost across molluscs. Similarly, the analysed mollusc RAR were unresponsive towards organochloride pesticides. In contrast, transcriptional repressions were observed with the RAR/RXR unit upon exposure to retinoids or RXR-specific ligands. Loss-of-function and gain-of-function mutations further corroborate the obtained results and suggest that the repressive behaviour, observed with mollusc and human RAR/RXR heterodimers, is possibly mediated by ligand biding to RXR.

Species-specific accumulation and temporal trends of bisphenols and benzophenones in mollusks from the Chinese Bohai Sea during 2006-2015

Information on the occurrence and bioaccumulation of bisphenols and benzophenones in coastal marine invertebrates is limited. In this study, concentrations of eight bisphenol and five benzophenone analogues were determined in 186 mollusks collected from coastal areas of the Chinese Bohai Sea during the period 2006-2015. Total concentrations of bisphenols and benzophenones were in range of not detected (nd)-58 (geometric mean: 13.0 ng/g) and nd-59.1 (2.06 ng/g) on a dry-weight basis, respectively. BPA and BPF were the major bisphenols, collectively accounting for >90% of the total concentrations. BP-3 was the predominant benzophenone, representing 74% of the total concentrations. The mollusk species, Meretrix meretrix, accumulated high concentrations of both bisphenols and benzophenones. A steady increase in bisphenol concentrations in mollusks was observed in recent years, whereas no obvious temporal trend was found for benzophenones. The estimated daily intakes of bisphenols through consumption of mollusks were lower than the current reference dose. This study establishes a baseline concentration for bisphenols and benzophenones in mollusks in Chinese coastal waters.

Bioaccumulation of heavy metals in fish, crustaceans, molluscs and echinoderms from the Tuscany coast

The concentration of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were analyzed in the edible part of several species of fish, crustaceans, molluscs and echinoderms collected in sensitive areas of the Tuscany coast (northern Italy). The concentration of As (0.39-78.1 μg g^-1) and Hg (0.01-1.56 μg g^-1) resulted in most cases higher than reference thresholds. Target hazard quotient (THQ) and lifetime cancer risk (TR) indexes were calculated to assess cancer and non-cancer risk due to oral exposure; the highest THQ values referred to As and Hg, with values ≥ 1 in 39% and 48% of cases, respectively. Total target hazard quotients (TTHQ) values suggested that the local population could experience adverse health effects due to consumption of local seafood, mainly of demersal and benthic species. Cancer risk was mainly associated with As exposure, and with Cd intake, especially through molluscs consumption. The NMDS model highlighted species specific bioaccumulation processes and specific sensitivity of species to different bioavailable heavy metals. Specifically, Mullus spp. and Scorpaena porcus preferentially accumulate Hg and Cr, Octopus vulgaris specimens were discriminated by the presence of Pb and Zn, while an evident preference for Cd and Cu was recorded in Squilla mantis. In addition, the distribution of heavy metals in organisms revealed sound differences between Follonica and Livorno sampling sites, demonstrating a highly heterogeneous anthropogenic impact in terms of heavy metals input from the industrial activity resting on land.

Identification, Characterization, and Expression Analysis of a FMRFamide-Like Peptide Gene in the Common Chinese Cuttlefish (Sepiella japonica)

The peptide FMRFamide is one of the well-known peptides involved in multiple physiological processes in the phylum Mollusca. In this study, a FMRFamide gene (GenBank accession No. KJ933411) was identified in a cuttlefish species called Sepiella japonica and was designated as SjFMRFamide. The total length of the SjFMRFamide sequence was found to be 1880 bp while the open reading frame contained 996 bp encoding a protein of 331 amino acid residues with a predicted isoelectric point (pI) and molecular weight (MW) of 9.18 and 38.8 kDa along with a 333 bp 5'-untranslated region (UTR) and 551 bp 3'-UTR. The deduced SjFMRFamide precursor protein contains one signal peptide and expresses four kinds FMRFamide-related peptides including a single copy of FLRFamide, ALSGDAFLRFamide, and FIRFamide and multiple copies of FMRFamide. Results of phylogenetic relation analysis strongly indicated that the sequence of this gene shares high identity with the genes of known FMRFamides. Spatial expression analysis indicated the highest mRNA expression of SjFMRFamide in the brain of male and female cuttlefishes among the eight tissues analyzed. An in situ hybridization assay of the brain indicated that SjFMRFamide was transcribed in several functional lobes, which suggests that it might be related to many physiological regulatory mechanisms. This is the first study describing FMRFamide in S. japonica and the results may contribute to future studies of neuropeptide evolution or may prove useful for the development of aquaculture methods for this cuttlefish species.

Uncovering the metabolic response of abalone (Haliotis midae) to environmental hypoxia through metabolomics

INTRODUCTION

Oxygen is essential for metabolic processes and in the absence thereof alternative metabolic pathways are required for energy production, as seen in marine invertebrates like abalone. Even though hypoxia has been responsible for significant losses to the aquaculture industry, the overall metabolic adaptations of abalone in response to environmental hypoxia are as yet, not fully elucidated.

OBJECTIVE

To use a multiplatform metabolomics approach to characterize the metabolic changes associated with energy production in abalone (Haliotis midae) when exposed to environmental hypoxia.

METHODS

Metabolomics analysis of abalone adductor and foot muscle, left and right gill, hemolymph, and epipodial tissue samples were conducted using a multiplatform approach, which included untargeted NMR spectroscopy, untargeted and targeted LC-MS spectrometry, and untargeted and semi-targeted GC-MS spectrometric analyses.

RESULTS

Increased levels of anaerobic end-products specific to marine animals were found which include alanopine, strombine, tauropine and octopine. These were accompanied by elevated lactate, succinate and arginine, of which the latter is a product of phosphoarginine breakdown in abalone. Primarily amino acid metabolism was affected, with carbohydrate and lipid metabolism assisting with anaerobic energy production to a lesser extent. Different tissues showed varied metabolic responses to hypoxia, with the largest metabolic changes in the adductor muscle.

CONCLUSIONS

From this investigation, it becomes evident that abalone have well-developed (yet understudied) metabolic mechanisms for surviving hypoxic periods. Furthermore, metabolomics serves as a powerful tool for investigating the altered metabolic processes in abalone.

Detection of Nitric Oxide via Electronic Paramagnetic Resonance in Mollusks

Electronic paramagnetic resonance (EPR) is an appropriate tool to identify free radicals formed in tissues under normal as well as stressful conditions. Since nitric oxide (NO) as a free radical has paramagnetic properties it can be detected by EPR. The use of spin traps highly improves the sensitivity allowing NO identification, detection and quantification at room temperature in vitro and in vivo conditions. NO production in animals is almost exclusively associated to an enzyme family known as Nitric Oxide Synthases (NOSs). The digestive glands of mollusks are a major target for oxidative disruption related to environmental stress. A simple EPR-methodology to asses both, the presence of NO and its rate of generation in tissues from different mollusk species, is reported here.

Fifteen years of imposex and tributyltin pollution monitoring along the Portuguese coast

IMO's Anti-Fouling Systems convention banned the use of organotin-based antifouling systems in 2008 as the ultimate effort to stop tributyltin (TBT) inputs into the marine environment. One of the hazardous effects of TBT is imposex (the superimposition of male sexual characters onto gastropod females), a phenomenon that may cause female sterility and the gastropod populations decline. Despite previous European Union legislation had already been shown effective in reducing the imposex levels along the Portuguese coast, this study intends to confirm these decreasing trends after 2008 and describe the global evolution in the last 15 years. Imposex levels were assessed in two bioindicators - the dog-whelk Nucella lapillus and the netted-whelk Nassarius reticulatus (Gastropoda, Prosobranchia) - in 2011 and 2014, and the results were compared with previous years. Both species showed progressive decreasing trends in imposex levels over the last 15 years; median values of the vas deferens sequence index (VDSI) fell from 3.96 to 0.78 in N. lapillus and from 3.39 to 0.29 in N. reticulatus. The temporal/spatial evolution of imposex suggests an apparent shift of TBT hotspots, being now restricted to fishing ports and marinas in detriment of large commercial harbours where TBT levels fell rapidly. Butyltins were measured in the whole tissues of N. lapillus females collected in 2014: monobutyltin (MBT) varied from < DL (detection limit: 1 ng Sn/g) to 13 ng Sn/g dw, dibutyltin (DBT) from 2.2 to 27 ng Sn/g dw and TBT from 1.5 to 55 ng Sn/g dw. Although TBT body burden has declined over time, the butyltin degradation index ([MBT]+[DBT])/[TBT] exhibited values < 1 in c. a. 90% of the sites assessed, suggesting that recent TBT inputs are still widespread in the Portuguese coast eventually due to illegal use of TBT antifouling systems and TBT desorption from sediments.

Co-Option and De Novo Gene Evolution Underlie Molluscan Shell Diversity

Molluscs fabricate shells of incredible diversity and complexity by localized secretions from the dorsal epithelium of the mantle. Although distantly related molluscs express remarkably different secreted gene products, it remains unclear if the evolution of shell structure and pattern is underpinned by the differential co-option of conserved genes or the integration of lineage-specific genes into the mantle regulatory program. To address this, we compare the mantle transcriptomes of 11 bivalves and gastropods of varying relatedness. We find that each species, including four Pinctada (pearl oyster) species that diverged within the last 20 Ma, expresses a unique mantle secretome. Lineage- or species-specific genes comprise a large proportion of each species’ mantle secretome. A majority of these secreted proteins have unique domain architectures that include repetitive, low complexity domains (RLCDs), which evolve rapidly, and have a proclivity to expand, contract and rearrange in the genome. There are also a large number of secretome genes expressed in the mantle that arose before the origin of gastropods and bivalves. Each species expresses a unique set of these more ancient genes consistent with their independent co-option into these mantle gene regulatory networks. From this analysis, we infer lineage-specific secretomes underlie shell diversity, and include both rapidly evolving RLCD-containing proteins, and the continual recruitment and loss of both ancient and recently evolved genes into the periphery of the regulatory network controlling gene expression in the mantle epithelium.

Differential toxic effects of Ulva lactuca (Chlorophyta) on the herbivorous gastropods, Littorina littorea and L. obtusata (Mollusca)

Members of the genus Ulva are widespread and abundant in intertidal and shallow subtidal areas but there are conflicting data regarding susceptibility to herbivory. While some studies have documented that Ulva spp. were favored by a diversity of marine herbivores, other work has revealed herbivore deterrence. We investigated grazing and growth rates of the littorinid species, Littorina littorea and L. obtusata, when offered Fucus vesiculosus, Ascophyllum nodosum, Ulva lactuca, and Chondrus crispus, highlighting distinctive vulnerabilities to toxic effects of U. lactuca. Ulva lactuca was the preferred food of L. littorea, while L. obtusata showed no grazing on this ephemeral algal species. In contrast, F. vesiculosus was highly preferred by L. obtusata. Although L. littorea demonstrated a grazing preference for U. lactuca, growth rate of this gastropod species was nearly 3× greater when fed F. vesiculosus, suggesting a non-lethal, negative effect of U. lactuca on L. littorea with long-term exposure. Mortality of L. obtusata ranged from 0% to 100% when held in the presence of various Ulva densities for 1 week, and Ulva exudate depressed herbivory of this gastropod. We conclude that the water-soluble, toxic exudate produced by U. lactuca in response to herbivory had allelochemical properties, and may contain a cleavage product (acrylic acid) of dimethylsulfoniopropionate or reactive oxygen species (i.e., H₂ O₂ ). Observed differences in susceptibility to Ulva toxicity by the littorinid species may be related to generalist versus specialist feeding and habitat strategies.

Toxicological perspective on the osmoregulation and ionoregulation physiology of major ions by freshwater animals: Teleost fish, crustacea, aquatic insects, and Mollusca

Anthropogenic sources increase freshwater salinity and produce differences in constituent ions compared with natural waters. Moreover, ions differ in physiological roles and concentrations in intracellular and extracellular fluids. Four freshwater taxa groups are compared, to investigate similarities and differences in ion transport processes and what ion transport mechanisms suggest about the toxicity of these or other ions in freshwater. Although differences exist, many ion transporters are functionally similar and may belong to evolutionarily conserved protein families. For example, the Na+ /H+ -exchanger in teleost fish differs from the H+ /2Na+ (or Ca2+ )-exchanger in crustaceans. In osmoregulation, Na+ and Cl- predominate. Stenohaline freshwater animals hyperregulate until they are no longer able to maintain hypertonic extracellular Na+ and Cl- concentrations with increasing salinity and become isotonic. Toxic effects of K+ are related to ionoregulation and volume regulation. The ionic balance between intracellular and extracellular fluids is maintained by Na+ /K+ -adenosine triphosphatase (ATPase), but details are lacking on apical K+ transporters. Elevated H+ affects the maintenance of internal Na+ by Na+ /H+ exchange; elevated HCO3- inhibits Cl- uptake. The uptake of Mg2+ occurs by the gills or intestine, but details are lacking on Mg2+ transporters. In unionid gills, SO42- is actively transported, but most epithelia are generally impermeant to SO42- . Transporters of Ca2+ maintain homeostasis of dissolved Ca2+ . More integration of physiology with toxicology is needed to fully understand freshwater ion effects. Environ Toxicol Chem 2017;36:576-600. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Cross-talk among immune and neuroendocrine systems in molluscs and other invertebrate models

The comparison between immune and neuroendocrine systems in vertebrates and invertebrates suggest an ancient origin and a high degree of conservation for the mechanisms underlying the integration between immune and stress responses. This suggests that in both vertebrates and invertebrates the stress response involves the integrated network of soluble mediators (e.g., neurotransmitters, hormones and cytokines) and cell functions (e.g., chemotaxis and phagocytosis), that interact with a common objective, i.e., the maintenance of body homeostasis. During evolution, several changes observed in the stress response of more complex taxa could be the result of new roles of ancestral molecules, such as ancient immune mediators may have been recruited as neurotransmitters and hormones, or vice versa. We review older and recent evidence suggesting that immune and neuro-endocrine functions during the stress response were deeply intertwined already at the dawn of multicellular organisms. These observations found relevant reflections in the demonstration that immune cells can transdifferentiate in olfactory neurons in crayfish and the recently re-proposed neural transdifferentiation in humans.

Anatomical and physiological background permitting spatial odor sensation in stylommatophoran molluscs

Earlier experiments demonstrated that in order to place protracted tentacles and thereby olfactory receptors in an appropriate position for optimal perception of odor stimuli extraordinary complex movements are required. Until recently both large scale tentacle movements and patterned tentacle movements have been attributed to the concerted involvement of the tentacle retractor muscle and muscles of tegumentum. Recently the existence of three novel muscles in the posterior tentacles of Helix has been discovered. The present review, based on experimental data obtained by our research group, outlines the anatomy, physiology and pharmacology of these muscles that enable the tentacles to execute complex movements observed during foraging both in naïve and food-conditioned snails. Our findings are also compared as far as possible with earlier and recent data obtained on innervation characteristics and pharmacology of molluscan muscles.

Phthalate monoesters as markers of phthalate contamination in wild marine organisms

The level of phthalate esters (PAEs) alone is not considered to be a sufficient indicator of PAE pollution due to the quick metabolism of PAEs in the biota. The primary metabolites of PAEs, monoalkyl phthalate esters (MPEs), may also be an important indicator. However, PAE metabolism has scarcely been documented in wild marine organisms. We analysed five PAEs [dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), di(2-ethylhexyl) phthalate (DEHP), and di-n-octyl phthalate (DNOP)] and their corresponding MPEs [mono-methyl phthalate (MMP), mono-ethyl phthalate (MEP), mono-n-butyl phthalate (MBP), mono-2-ethylhexyl phthalate (MEHP), and mono-n-octyl phthalate (MNOP)] in 95 wild aquatic marine samples (including fish, prawns and molluscs) collected from the Yangtze River Delta area of the East China Sea. The species-dependent distribution of these compounds was associated with the food habits, living patterns and trophic levels of the biota. Slightly higher levels of hydrophobic PAEs (DBP and DEHP, logK_OW 4.27 and 7.33, respectively) were observed in fish species consuming benthic organisms or in demersal fish species, suggesting the importance of benthic organisms and sediment. Trophic dilution of both PAEs and MPEs implies further metabolic transformation at higher trophic levels. MPE tissue distributions in fish demonstrate that the highest concentrations were always observed in bile. Metabolism via the kidney and gill is a probable main way for the relatively less hydrophobic MPEs (logK_OW = <4.73, from MMP to MEHP), whereas metabolism via the liver is likely the main way for the most hydrophobic MNOP (logK_OW 5.22). Generally, higher detection frequencies of MPEs were observed than those of parent PAEs. Significant liner correlations were observed between the levels of short-branched (carbon atom per chain = <4) MPEs and the sum of PAEs and MPEs (n = 95, p < 0.01), demonstrating that short-branched MPEs can be used as biomarkers of exposure to quantitatively reflect parent PAE contamination in wild marine organisms.

Potential mechanisms underlying estrogen-induced expression of the molluscan estrogen receptor (ER) gene

In vertebrates, estrogens and estrogen mimicking chemicals modulate gene expression mainly through a genomic pathway mediated by the estrogen receptors (ERs). Although the existence of an ER orthologue in the mollusc genome has been known for some time, its role in estrogen signalling has yet to be deciphered. This is largely due to its constitutive (ligand-independent) activation and a limited mechanistic understanding of its regulation. To fill this knowledge gap, we cloned and characterised an ER cDNA (sgER) and the 5'-flanking region of the gene from the Sydney rock oyster Saccostrea glomerata. The sgER cDNA is predicted to encode a 477-amino acid protein that contains a DNA-binding domain (DBD) and a ligand-binding domain (LBD) typically conserved among both vertebrate and invertebrate ERs. A comparison of the sgER LBD sequence with those of other ligand-dependent ERs revealed that the sgER LBD is variable at several conserved residues known to be critical for ligand binding and receptor activation. Ligand binding assays using fluorescent-labelled E2 and purified sgER protein confirmed that sgER is devoid of estrogen binding. In silico analysis of the sgER 5'-flanking sequence indicated the presence of three putative estrogen responsive element (ERE) half-sites and several putative sites for ER-interacting transcription factors, suggesting that the sgER promoter may be autoregulated by its own gene product. sgER mRNA is ubiquitously expressed in adult oyster tissues, with the highest expression found in the ovary. Ovarian expression of sgER mRNA was significantly upregulated following in vitro and in vivo exposure to 17β-estradiol (E2). Notably, the activation of sgER expression by E2 in vitro was abolished by the specific ER antagonist ICI 182, 780. To determine whether sgER expression is epigenetically regulated, the in vivo DNA methylation status of the putative proximal promoter in ovarian tissues was assessed using bisulfite genomic sequencing. The results showed that the promoter is predominantly hypomethylated (with 0-3.3% methylcytosines) regardless of sgER mRNA levels. Overall, our investigations suggest that the estrogen responsiveness of sgER is regulated by a novel ligand-dependent receptor, presumably via a non-genomic pathway(s) of estrogen signalling.

Transcriptome of the Australian Mollusc Dicathais orbita Provides Insights into the Biosynthesis of Indoles and Choline Esters

Dicathais orbita is a mollusc of the Muricidae family and is well known for the production of the expensive dye Tyrian purple and its brominated precursors that have anticancer properties, in addition to choline esters with muscle-relaxing properties. However, the biosynthetic pathways that produce these secondary metabolites in D. orbita are not known. Illumina HiSeq 2000 transcriptome sequencing of hypobranchial glands, prostate glands, albumen glands, capsule glands, and mantle and foot tissues of D. orbita generated over 201 million high quality reads that were de novo assembled into 219,437 contigs. Annotation with reference to the Nr, Swiss-Prot and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases identified candidate-coding regions in 76,152 of these contigs, with transcripts for many enzymes in various metabolic pathways associated with secondary metabolite biosynthesis represented. This study revealed that D. orbita expresses a number of genes associated with indole, sulfur and histidine metabolism pathways that are relevant to Tyrian purple precursor biosynthesis, and many of which were not found in the fully annotated genomes of three other molluscs in the KEGG database. However, there were no matches to known bromoperoxidase enzymes within the D. orbita transcripts. These transcriptome data provide a significant molecular resource for gastropod research in general and Tyrian purple producing Muricidae in particular.

Metals and PCB levels in some edible marine organisms from the Ionian Sea: dietary intake evaluation and risk for consumers

Concentrations of some metals (Cd, Cu, As, Hg, Pb) and polychlorinated biphenyls (PCBs) were investigated in edible marine organisms from different trophic levels and feeding behaviour like bivalve molluscs (Mytilus galloprovincialis and Chlamys glabra), gastropod molluscs (Hexaplex trunculus) and some commercial species of fish (Trachurus trachurus, Boops boops, Sarpa salpa and Gobius niger). These species were collected in the first inlet of the Mar Piccolo of Taranto (Ionian Sea, Southern Italy), classified as 'Site of National Interest' established by National Law 426 (1998) and included in the 'National Environmental Remediation and Restoration Projects'. The aim of this work was to investigate contamination levels and public health risks, associated with consuming seafood harvested from these areas. Moreover, in this study, was also estimated the weekly intake in children and adults, both for metals and PCBs. In comparison with the permissible limits set by EC Regulations, Cd and Pb levels were over the limit in the H. trunculus (in all sampling stations) and in the fish T. trachurus respectively. PCBs were over the legal limit in all sampled species with the exception of M. galloprovincialis (station 1), C. glabra and the herbivorous fish S. salpa. In the fish T. trachurus, for example, the concentration of six target PCBs was about five times higher than the EC limit. The estimated intakes of those trace elements included in this study through seafood consumption by the population exceed the provisional tolerable weekly intake recommended by the Joint FAO/WHO Expert Committee on Food Additives for Cd and Hg in the H. trunculus and T. trachurus, especially in children. Moreover, hazard quotience (HQ) for Hg and Cd was >1 in the children for T. trachurus and H. trunculus consumption. As regard non-dioxin-like PCB (NDL-PCB), the estimated intake were always above the 'provisional guidance value' (70 ng/kg body weight) Arnich et al. (Regul Toxicol Pharm 54: 287-2, 2009) for all sampled organism. Thus, health risks due to the dietary Hg, Cd and PCBs intake, especially for children, cannot be excluded. Therefore, an extended remediation programme is necessary to safeguard marine ecosystem, human health and, not less important, the economic activities, in the Taranto marine area.

Anticoagulant Activity and Structural Characterization of Polysaccharide from Abalone (Haliotis discus hannai Ino) Gonad

In this study, we aimed at characterizing the structure and the anticoagulant activity of a polysaccharide fraction (AGP33) isolated from the gonads of Haliotis discus hannai Ino. AGP33 was extracted by enzymatic hydrolysis and purified by ion-exchange and gel-filtration chromatography. The backbone fraction of AGP33 (BAGP33), which appeared to contain of mannose, glucose and galactose, was prepared by partial acid hydrolysis. According to methylation and nuclear magnetic resonance (NMR) spectroscopy, the backbone of AGP33 was identified as mainly consisting of 1→3-linked, 1→4-linked, and 1→6-linked monosaccharides. AGP33 is a sulfated polysaccharide with sulfates occur at 3-O- and 4-O-positions. It prolonged thromboplastin time (APTT), thrombin time (TT) and prothrombin time (PT) compared to a saline control solution in a dosage-dependent manner. AGP33 exhibited an extension (p < 0.01) of APTT compared to the saline group at concentrations higher than 5 μg/mL. AGP33 exhibited higher anticoagulant activity than its desulfated product (AGP33-des) and BAGP33. The results showed that polysaccharide with higher molecular weight and sulfate content demonstrated greater anticoagulant activity.

A mollusk VDR/PXR/CAR-like (NR1J) nuclear receptor provides insight into ancient detoxification mechanisms

The origin and diversification of the metazoan endocrine systems represents a fundamental research issue in biology. Nuclear receptors are critical components of these systems. A particular group named VDR/PXR/CAR (NR1I/J) is central in the mediation of detoxification responses. While orthologues have been thoroughly characterized in vertebrates, a sparse representation is currently available for invertebrates. Here, we provide the first isolation and characterization of a lophotrochozoan protostome VDR/PXR/CAR nuclear receptor (NR1J), in the estuarine bivalve the peppery furrow shell (Scrobicularia plana). Using a reporter gene assay, we evaluated the xenobiotic receptor plasticity comparing the human PXR with the S. plana NR1Jβ. Our results show that the molluscan receptor responds to a natural toxin (okadaic acid) in a similar fashion to that reported for other invertebrates. In contrast, the pesticide esfenvalerate displayed a unique response, since it down regulated transactivation at higher concentrations, while for triclosan no response was observed. Additionally, we uncovered lineage specific gene duplications and gene loss in the gene group encoding NRs in protostomes with likely impacts on the complexity of detoxification mechanisms across different phyla. Our findings pave the way for the development of multi-specific sensor tools to screen xenobiotic compounds acting via the NR1I/J group.

Antibacterial Derivatives of Marine Algae: An Overview of Pharmacological Mechanisms and Applications

The marine environment is home to a taxonomically diverse ecosystem. Organisms such as algae, molluscs, sponges, corals, and tunicates have evolved to survive the high concentrations of infectious and surface-fouling bacteria that are indigenous to ocean waters. Both macroalgae (seaweeds) and microalgae (diatoms) contain pharmacologically active compounds such as phlorotannins, fatty acids, polysaccharides, peptides, and terpenes which combat bacterial invasion. The resistance of pathogenic bacteria to existing antibiotics has become a global epidemic. Marine algae derivatives have shown promise as candidates in novel, antibacterial drug discovery. The efficacy of these compounds, their mechanism of action, applications as antibiotics, disinfectants, and inhibitors of foodborne pathogenic and spoilage bacteria are reviewed in this article.