Organic compounds in the extrapalial fluid and haemolymph of Anodonta cygnea (L.) with emphasis on the seasonal biomineralization process

Biologically driven isotopic fractionations in bivalves: from palaeoenvironmental problem to palaeophysiological proxy

Traditional bulk stable isotope (δ18 O and δ13 C) and clumped isotope (Δ47 ) records from bivalve shells provide invaluable histories of Earth's local and global climate change. However, biologically driven isotopic fractionations (BioDIFs) can overprint primary environmental signals in the shell. Here, we explore how conventional measurements of δ18 O, δ13 C, and Δ47 in bivalve shells can be re-interpreted to investigate these physiological processes deliberately. Using intrashell Δ47 and δ18 O alignment as a proxy for equilibrium state, we separately examine fractionations and/or disequilibrium occurring in the two major stages of the biomineralisation process: the secretion of the extrapallial fluid (EPF) and the precipitation of shell material from the EPF. We measured δ18 O, δ13 C, and Δ47 in fossil shells representing five genera (Lahillia, Dozyia, Eselaevitrigonia, Nordenskjoldia, and Cucullaea) from the Maastrichtian age [66-69 million years ago (Ma)] López de Bertodano Formation on Seymour Island, Antarctica. Material was sampled from both the outer and inner shell layers (OSL and ISL, respectively), which precipitate from separate EPF reservoirs. We find consistent δ18 O values across the five taxa, indicating that the composition of the OSL can be a reliable palaeoclimate proxy. However, relative to the OSL baseline, ISLs of all taxa show BioDIFs in one or more isotopic parameters. We discuss/hypothesise potential origins of these BioDIFs by synthesising isotope systematics with the physiological processes underlying shell biomineralisation. We propose a generalised analytical and interpretive framework that maximises the amount of palaeoenvironmental and palaeobiological information that can be derived from the isotopic composition of fossil shell material, even in the presence of previously confounding 'vital effects'. Applying this framework in deep time can expand the utility of δ18 O, δ13 C, and Δ47 measurements from proxies of past environments to proxies for certain biomineralisation strategies across space, time, and phylogeny among Bivalvia and other calcifying organisms.

The mantle exosome proteins of Hyriopsis cumingii participate in shell and nacre color formation

Pearl color is closely related to the nacre color of shell in Hyriopsis cumingii, and pearl color has a huge impact on its price. The nacre is an important part of the shell, and studies have suggested that mantle exosomes participated in shell formation. Exosomes contain many different proteins that are involved in different biological processes. In this study, exosomes were extracted from mantles of mussels with different nacre color. TMT quantitative proteome sequencing analysis was performed on purple and white mussel mantle exosomes, and 4861 proteins were obtained. Based on the standard of (|log2 (Fold change)| ≥ 1.2 or ≤ 0.83 and p-value ≤ 0.05), a total of 758 differentially expressed proteins were found. Some proteins involved in shell and nacre color formation were predicted with the proteins annotate, GO classification system. Moreover, 14 differentially expressed proteins (including eight up-regulated proteins and six down-regulated proteins) were validated using parallel reaction monitoring (PRM) assays. Overall, this information will be useful to improve our understanding of the molecular mechanisms of shell and nacre color formation in H. cumingii.

Bioinspired Materials: From Living Systems to New Concepts in Materials Chemistry

Nature successfully employs inorganic solid-state materials (i.e., biominerals) and hierarchical composites as sensing elements, weapons, tools, and shelters. Optimized over hundreds of millions of years under evolutionary pressure, these materials are exceptionally well adapted to the specifications of the functions that they perform. As such, they serve today as an extensive library of engineering solutions. Key to their design is the interplay between components across length scales. This hierarchical design—a hallmark of biogenic materials—creates emergent functionality not present in the individual constituents and, moreover, confers a distinctly increased functional density, i.e., less material is needed to provide the same performance. The latter aspect is of special importance today, as climate change drives the need for the sustainable and energy-efficient production of materials. Made from mundane materials, these bioceramics act as blueprints for new concepts in the synthesis and morphosynthesis of multifunctional hierarchical materials under mild conditions. In this review, which also may serve as an introductory guide for those entering this field, we demonstrate how the pursuit of studying biomineralization transforms and enlarges our view on solid-state material design and synthesis, and how bioinspiration may allow us to overcome both conceptual and technical boundaries.

Molecular and functional analysis of PmCHST1b in nacre formation of Pinctada fucata martensii

Keratan sulfate possesses considerable amounts of negatively charged sulfonic acid groups and participates in biomineralization. In the present study, we investigated characteristics and functions of a CHST1 gene identified from the pearl oyster Pinctada fucata martensii (PmCHST1b) which participated in the synthesis of keratan sulfate. PmCHST1b amino acid sequence carried a typical sulfotransferase-3 domain (sulfotransfer-3 domain) and belonged to membrane-associated sulfotransferases. Homologous analysis of CHST1 from different species showed the conserved motif (5' PSB motif and 3' PB motif) which interacted with 3'-phosphoadenosine-5'-phosphosulfate (PAPS). Structure analysis of sulfotransferase domain indicted that PmCHST1b showed the conserved catalytic structure character and the relationships presented in the phylogenetic tree conformed to that of traditional taxonomy. Expression pattern of PmCHST1b in different tissues and development stages showed that PmCHST1b widely expressed in all the detected tissues and development stages and showed the highest expression level in the central zone of mantle (MC). PmCHST1b expressed highly in the trochophore, D-stage larvae and spat which corresponded to prodissoconch and dissoconch shell formation, respectively. RNA interference (RNAi) successfully inhibited expression level of PmCHST1b in MC (P<0.05), and sulfate polymer content in the extrapallial fluid significantly reduced (P<0.05). Crystallization of shell nacre became irregular. Results above indicated that PmCHST1b may affect nacre formation by participating in synthesis of keratan sulfate in extrapallial fluid. This study provided fundamental materials for further research on the role of sulfotransferases and keratan sulfate in nacre formation.

MSP22.8 is a protease inhibitor-like protein involved in shell mineralization in the edible mussel Mytilus galloprovincialis

The mussel shell protein 22.8 (MSP22.8) is recognized by a monoclonal antibody (M22.8) directed against larvae of the mussel Mytilus galloprovincialis. After being secreted by cells of the mantle-edge epithelium into the extrapallial (EP) space (the gap between the mantle and the shell), the protein is detected in the extrapallial fluid (EPF) and EP hemocytes and finally becomes part of the shell matrix framework in adult specimens of M. galloprovincialis. In the work described here, we show how MSP22.8 is detected in EPF samples from different species of mussels (M. galloprovincialis, Mytilus edulis, and Xenostrobus securis), and also as a shell matrix protein in M. galloprovincialis, Mytilus chilensis, and Perna canaliculus. A multistep purification strategy was employed to isolate the protein from the EPF, which was then analyzed by mass spectrometry in order to identify it. The results indicate that MSP22.8 is a serpin-like protein that has great similarity with the protease inhibitor-like protein-B1, reported previously for Mytilus coruscus. We suggest that MSP22.8 is part of a system offering protection from proteolysis during biomineralization and is also part of the innate immune system in mussels.

Hyriopsis cumingii Hic52-A novel nacreous layer matrix protein with a collagen-like structure

Nacre is a product of a precisely regulated biomineralization process and a major contributor to the luster of pearls. Nacre is composed of calcium carbonate and an organic matrix of proteins that is secreted from mollusc mantle tissue and is exclusively associated with shell formation. In this study, hic52, a novel matrix protein gene from mantle of Hyriopsis cumingii, was cloned and functionally analyzed. The full-length cDNA of hic52 encoded 542 amino acids and contained a signal peptide of 18 amino acids. Excluding the signal peptide, the theoretical molecular mass of the polypeptide was 52.2kDa. The predicted isoelectric point was 10.37, indicating a basic shell protein. The amino acid sequence of hic52 featured high proportion of Gly (28.8%) and Gln (12.4%) residues. The predicted tertiary structure was characterized as having similarities to collagen I, alpha 1 and alpha 2 in the structure. The polypeptide sequence shared no homology with collagen. The hic52 expression pattern by quantitative real-time PCR and in situ hybridization exhibits at the dorsal epithelial cells of the mantle. Expression increased during the stages of pearl sac development. The data showed that hic52 is probably a framework shell protein that mediates and controls the nacreous biomineralization process.

Characterization of a Monoclonal Antibody Directed against Mytilus spp Larvae Reveals an Antigen Involved in Shell Biomineralization

The M22.8 monoclonal antibody (mAb) developed against an antigen expressed at the mussel larval and postlarval stages of Mytilus galloprovincialis was studied on adult samples. Antigenic characterization by Western blot showed that the antigen MSP22.8 has a restricted distribution that includes mantle edge tissue, extrapallial fluid, extrapallial fluid hemocytes, and the shell organic matrix of adult samples. Other tissues such as central mantle, gonadal tissue, digestive gland, labial palps, foot, and byssal retractor muscle did not express the antigen. Immunohistochemistry assays identified MSP22.8 in cells located in the outer fold epithelium of the mantle edge up to the pallial line. Flow cytometry analysis showed that hemocytes from the extrapallial fluid also contain the antigen intracellularly. Furthermore, hemocytes from hemolymph have the ability to internalize the antigen when exposed to a cell-free extrapallial fluid solution. Our findings indicate that hemocytes could play an important role in the biomineralization process and, as a consequence, they have been included in a model of shell formation. This is the first report concerning a protein secreted by the mantle edge into the extrapallial space and how it becomes part of the shell matrix framework in M. galloprovincialis mussels.

Light induces changes in activities of Na(+)/K(+)-ATPase, H(+)/K(+)-ATPase and glutamine synthetase in tissues involved directly or indirectly in light-enhanced calcification in the giant clam, Tridacna squamosa

The objective of this study was to determine the effects of 12 h of exposure to light, as compared with 12 h of exposure to darkness (control), on enzymatic activities of transporters involved in the transport of NH(+) 4 or H(+), and activities of enzymes involved in converting NH(+) 4 to glutamate/glutamine in inner mantle, outer mantle, and ctenidia of the giant clam, Tridacna squamosa. Exposure to light resulted in a significant increase in the effectiveness of NH(+) 4 in substitution for K(+) to activate Na(+)/K(+)-ATPase (NKA), manifested as a significant increase in the Na(+)/NH(+) 4-activated-NKA activity in the inner mantle. However, similar phenomena were not observed in the extensible outer mantle, which contained abundant symbiotic zooxanthellae. Hence, during light-enhanced calcification, H(+) released from CaCO3 deposition could react with NH3 to form NH(+) 4 in the extrapallial fluid, and NH(+) 4 could probably be transported into the shell-facing inner mantle epithelium through NKA. Light also induced an increase in the activity of glutamine synthetase, which converts NH(+) 4 and glutamate to glutamine, in the inner mantle. Taken together, these results explained observations reported elsewhere that light induced a significant increase in pH and a significant decrease in ammonia concentration in the extrapallial fluid, as well as a significant increase in the glutamine concentration in the inner mantle, of T. squamosa. Exposure of T. squamosa to light also led to a significant decrease in the N-ethylmaleimide (NEM)-sensitive-V-H(+)-ATPase (VATPase) in the inner mantle, and significant increases in the Na(+)/K(+)-activated-NKA, H(+)/NH(+) 4-activated-H(+)/K(+)-ATPase, and NEM-sensitive-VATPase activities in ctenidia, indicating that light-enhanced calcification might perturb Na(+) homeostasis and acid/base balance in the hemolymph, and might involve the active uptake of NH(+) 4 from the environment. This is the first report on light having direct enhancing effects on activities of certain transporters/enzymes related to light-enhanced calcification in the inner mantle and ctenidia of T. squamosa.

Biomineralization studies on cellulose membrane exposed to biological fluids of Anodonta cygnea

The present work proposes to analyse the results obtained under in vitro conditions where cellulose artificial membranes were incubated with biological fluids from the freshwater bivalve Anodonta cygnea. The membranes were mounted between two half 'Ussing chambers' with different composition solutions in order to simulate epithelial surfaces separating organic fluid compartments. The membrane surfaces were submitted to two synthetic calcium and phosphate solutions on opposite sides, at pH 6.0, 7.0 or 9.0 during a period of 6 hours. Additional assays were accomplished mixing these solutions with haemolymph or extrapallial fluid from A. cygnea, only on the calcium side. A selective ion movement, mainly dependent on the membrane pore size and/or cationic affinity, occurred with higher permeability for calcium ions to the opposite phosphate chamber supported by calcium diffusion forces across the cellulose membrane. In general, this promoted a more intense mineral precipitation on the phosphate membrane surface. A strong deposition of calcium phosphate mineral was observed at pH 9.0 as a primary layer with a homogeneous microstructure, being totally absent at pH 6.0. The membrane showed an additional crystal phase at pH 7.0 exhibiting a very particular hexagonal or cuttlebone shape, mainly on the phosphate surface. When organic fluids of A. cygnea were included, these crystal forms presented a high tendency to aggregate under rosaceous shapes, also predominantly in the phosphate side. The cellulose membrane was permeable to small organic molecules that diffused from the calcium towards the phosphate side. In the calcium side, very few similar crystals were observed. The presence of organic matrix from A. cygnea fluids induced a preliminary apatite-brushite crystal polymorphism. So, the present results suggest that cellulose membranes can be used as surrogates of biological epithelia with preferential ionic diffusion from the calcium to the phosphate side where the main mineral precipitation events occurred. Additionally, the organic fluids from freshwater bivalves should be also thoroughly researched in the applied biomedical field, as mineral nucleators and crystal modulators on biosynthetic systems.

Identification of housekeeping genes suitable for gene expression analysis in the pearl mussel, Hyriopsis cumingii, during biomineralization

Quantitative real-time polymerase chain reaction is a sensitive technique for quantifying gene expression levels. One or more appropriate reference genes must be selected to accurately compare mRNA transcript levels across different samples and tissues. The freshwater pearl, Hyriopsis cumingii (Lea), is an important economic species cultured in China. To date, no reference genes for gene expression analysis in this species have been validated. This study aimed to compare the relative expression of seven housekeeping genes across different tissue types and in the mantle or pearl sac during three biomineralization processes: seasonal shell growth, shell healing and pearl-sac formation in H. cumingii. Three programs evaluated the expression stabilities of the seven genes: BestKeeper, geNorm and NormFinder. The beta actin gene (ACTB), commonly used as a housekeeping gene in many studies, was the least stable. The expressions of Ubiquitin (Ubi) and Ribosomal protein L18 (Rpl18) and Elongation factor 1-alpha (EF1α) were more stable than the remaining four genes. Therefore, we suggest that Ubi, Rpl18 and EF1α are suitable reference genes. The three selected reference genes are expected to facilitate analysis of gene expressions during shell or pearl formation in H. cumingii.

Anomalous N-glycan structures with an internal fucose branched to GlcA and GlcN residues isolated from a mollusk shell-forming fluid

This report describes the structural details of a unique N-linked valence epitope on the major protein within the extrapallial (EP) fluid of the mollusk, Mytilus edulis. Fluids from this area are considered to be responsible for shell expansion by a self-assembly process that provides an organic framework for the growth of CaCO3 crystals. Previous reports from our laboratories have described the purification and amino acid sequence of this EP protein, which was found to be a glycoprotein (EPG) of approximately 28 KDa with 14.3% carbohydrate on a single N-linked consensus site. Described herein is the de novo sequence of the major glycan and its glycomers. The sequence was determined by ion trap sequential mass spectrometry (ITMS(n)) resolving structure by tracking precursor-product relationships through successive rounds of collision induced disassociation (CID), thereby spatially resolving linkage and branching details within the confines of the ion trap. Three major glycomers were detected, each possessing a 6-linked fucosylated N-linked core. Two glycans possessed four and five identical antennae, while the third possessed four antennas, but with an additional methylfucose 2-linked to the glucuronic acid moiety, forming a pentasaccharide. The tetrasaccharide structure was: 4-O-methyl-GlcA(1-4)[GlcNAc(1-3)]Fuc(1-4)GlcNAc, while the pentasaccharide was shown to be as follows: mono-O-methyl-Fuc(1-2)-4-O-methyl-GlcA(1-4)[GlcNAc(1-3)]Fuc(1-4)GlcNAc. Samples were differentially deuteriomethylated (CD3/CH3) to localize indigenous methylation, further analyzed by high resolution mass spectrometry (HRMS) to confirm monomer compositions, and finally gas chromatography mass spectrometry (GC-MS) to assign structural and stereoisomers. The interfacial shell surface location of this major extrapallial glycoprotein, its calcium and heavy metal binding properties and unique structure suggests a probable role in shell formation and possibly metal ion detoxification. A closely related terminal tetrasaccharide structure has been reported in spermatozoan glycolipids of freshwater bivalves.

Spatial analysis of biomineralization associated gene expression from the mantle organ of the pearl oyster Pinctada maxima

BACKGROUND

Biomineralization is a process encompassing all mineral containing tissues produced within an organism. One of the most dynamic examples of this process is the formation of the mollusk shell, comprising a variety of crystal phases and microstructures. The organic component incorporated within the shell is said to dictate this architecture. However general understanding of how this process is achieved remains ambiguous. The mantle is a conserved organ involved in shell formation throughout molluscs. Specifically the mantle is thought to be responsible for secreting the protein component of the shell. This study employs molecular approaches to determine the spatial expression of genes within the mantle tissue to further the elucidation of the shell biomineralization.

RESULTS

A microarray platform was custom generated (PmaxArray 1.0) from the pearl oyster Pinctada maxima. PmaxArray 1.0 consists of 4992 expressed sequence tags (ESTs) originating from mantle tissue. This microarray was used to analyze the spatial expression of ESTs throughout the mantle organ. The mantle was dissected into five discrete regions and analyzed for differential gene expression with PmaxArray 1.0. Over 2000 ESTs were determined to be differentially expressed among the tissue sections, identifying five major expression regions. In situ hybridization validated and further localized the expression for a subset of these ESTs. Comparative sequence similarity analysis of these ESTs revealed a number of the transcripts were novel while others showed significant sequence similarities to previously characterized shell related genes.

CONCLUSIONS

This investigation has mapped the spatial distribution for over 2000 ESTs present on PmaxArray 1.0 with reference to specific locations of the mantle. Expression profile clusters have indicated at least five unique functioning zones in the mantle. Three of these zones are likely involved in shell related activities including formation of nacre, periostracum and calcitic prismatic microstructure. A number of novel and known transcripts have been identified from these clusters. The development of PmaxArray 1.0, and the spatial map of its ESTs expression in the mantle has begun characterizing the molecular mechanisms linking the organics and inorganics of the molluscan shell.

Colloidal complexed silver and silver nanoparticles in extrapallial fluid of Mytilus edulis

Metal transport in mollusk extrapallial fluid (EPF) that acts as a "bridge" between soft tissues and shell has surprisingly received little attention until now. Using ultrafiltration and radiotracer techniques we determined silver concentrations and speciation in the EPF of the blue mussel Mytilus edulis after short-term uptake and depuration laboratory experiments. Radiolabelled silver ((¹¹⁰m)Ag) was used in dissolved or nanoparticulate phases (AgNPs < 40 nm), with a similar low Ag concentration (total radioactive and cold Ag ~0.7 μg/L) in a way that mussels could uptake radiotracers only from seawater. Our results indicated that silver nanoparticles were transported to the EPF of blue mussels at a level similar to the Ag ionic form. Bulk activity of radiolabelled silver in the EPF represented only up to 7% of the bulk activity measured in the whole mussels. The EPF extracted from mussels exposed to both treatments exhibited an Ag colloidal complexed form based on EPF ultrafiltration through a 3 kDa filter. This original study brings new insights to internal circulation of nanoparticles in living organisms and contributes to the international effort in studying the potential impacts of engineered nanomaterials on marine bivalves which play an essential role in coastal ecosystems, and are important contributors to human food supply from the sea.

Studies on a PMCA-like protein in the outer mantle epithelium of Anodonta cygnea: insights on calcium transcellular dynamics

Early studies on the outer mantle epithelium (OME) cells of the freshwater bivalve Anodonta cygnea (Linnaeus, 1758) revealed high ionic calcium concentrations by electrophysiological methods and subsequently a high tendency to reach an intracellular toxic condition. This toxicity could be neutralized by specific mechanisms in the cytosol of OME cells of A. cygnea. The present immunocytochemistry studies of OME cells by light and transmission electron microscopy (TEM) clearly showed a positive reaction of an antibody directed against the human plasma membrane Ca(2+)-ATPase 1 (PMCA-1) in the cytoplasm of OME cells. Also, western blot analysis of different fractions of OME cells with anti human PMCA-1 and C28R2 antibodies confirmed the presence of a PMCA-like protein with an unusual topographical localization and a molecular weight of only 70-80 kDa. These results lead us to speculate that this PMCA-like protein is distributed either in the plasma membrane or in the entire cytosol, where it eventually regulates intracellular calcium levels. Interestingly, the antibody reactions showed seasonal variations, being highest in OME samples prepared during summer when A. cygnea live under natural acidosis and absent in samples taken in winter conditions, which is in accordance with the seasonal variation of shell calcification rates. During winter, PMCA-1 antibody reaction was also detected in OME cells of animals kept only under experimentally induced acidosis conditions. Therefore, we assume that a functional role for this PMCA-like protein in the intracellular calcium regulation of OME cells during the mineralization of the shells of A. cygnea can be speculated.

Molluscan shell proteins: primary structure, origin, and evolution

In the last few years, the field of molluscan biomineralization has known a tremendous mutation, regarding fundamental concepts on biomineralization regulation as well as regarding the methods of investigation. The most recent advances deal more particularly with the structure of shell biominerals at nanoscale and the identification of an increasing number of shell matrix protein components. Although the matrix is quantitatively a minor constituent in the shell of mollusks (less than 5% w/w), it is, however, the major component that controls different aspects of the shell formation processes: synthesis of transient amorphous minerals and evolution to crystalline phases, choice of the calcium carbonate polymorph (calcite vs aragonite), organization of crystallites in complex shell textures (microstructures). Until recently, the classical paradigm in molluscan shell biomineralization was to consider that the control of shell synthesis was performed primarily by two antagonistic mechanisms: crystal nucleation and growth inhibition. New concepts and emerging models try now to translate a more complex reality, which is remarkably illustrated by the wide variety of shell proteins, characterized since the mid-1990s, and described in this chapter. These proteins cover a broad spectrum of pI, from very acidic to very basic. The primary structure of a number of them is composed of different modules, suggesting that these proteins are multifunctional. Some of them exhibit enzymatic activities. Others may be involved in cell signaling. The oldness of shell proteins is discussed, in relation with the Cambrian appearance of the mollusks as a mineralizing phylum and with the Phanerozoic evolution of this group. Nowadays, the extracellular calcifying shell matrix appears as a whole integrated system, which regulates protein-mineral and protein-protein interactions as well as feedback interactions between the biominerals and the calcifying epithelium that synthesized them. Consequently, the molluscan shell matrix may be a source of bioactive molecules that would offer interesting perspectives in biomaterials and biomedical fields.

Matrix proteins in the outer shells of molluscs

The shells of molluscs are composed mainly of calcium carbonate crystals, with small amounts of matrix proteins. For more than 50 years, they have attracted attention for their unique mechanical and biological properties. Only recently, however, have researchers begun to realize that it is the matrix proteins that control the formation of calcium carbonate crystals and play key roles in their extraordinary properties, despite the fact that matrix proteins comprise less than 5% of the shell weight. This article reviews the matrix proteins identified to date from the shells of molluscs, their structural characteristics, and their roles in shell formation. Some suggestions are given for further investigation based on the summary and analysis.

Isolation, purification and characterization of glycosaminoglycans in the fluids of the mollusc Anodonta cygnea

The isolation, purification and characterization of Anodonta cygnea haemolymph, and extrapallial fluid glycosaminoglycans (Gags), which have high calcium affinity, were carried out in order to better understand the process of nacreous shell biomineralization. Our results show the existence of two different Gags with similar contents in the two fluids, throughout the year, but with significant seasonal variations for both. In the winter months, we identified by electrophoresis, only one kind of Gag chain (hyaluronic acid) while two different Gags (hyaluronic acid and heparan sulphate-like) from both fluids of A. cygnea were found in summer months. Quantification showed the total Gag fractions of both fluids in average, at their highest concentration (79.8 mg/L) in the highest calcification summer period. In contrast, the period of the year with the lowest concentration of total Gags (54.6 mg/L) occurred during the winter when calcification is reduced. This significant decrease between seasons is correlated mainly with the sulphated fraction, being 37.1 mg/L in the summer while only 9.2 mg/L in the winter haemolymph. The present data suggest that a heparan sulphate-like Gag has a relevant role in the biomineralization mechanisms acting as the calcium carbonate nucleator in the shell.

Paracellular pathway in the shell epithelium ofAnodonta cygnea

Ultrastructural study of cell-cell connections in the outer mantle epithelium (OME) on high-pressure-frozen specimens revealed zonula adherens, septate junctions and gap junctions in Anodonta cygnea. In order to evaluate the permeability of the paracellular pathway, the OME was incubated under gradients of lanthanum and calcium. After lanthanum incubation (4 mM) from the basal side, the septate junctions were penetrated completely by this tracer. When applied from the apical side, lanthanum deposits were located similarly over the entire length of the septate junctions up to the first dilatations of the intercellular space. Calcium deposits were also present in paracellular areas only when OME had been incubated simultaneously with calcium (6 mM) and lanthanum (4 mM) gradients. Lanthanum and calcium deposits were detected with ESI (Electron Spectroscopic Imaging) and identified with EELS (Electron Energy Loss Spectroscopy). On the other hand, electrophysiological observations showed a 48% reduction of conductance when the OME was bathed on both sides with solutions containing lanthanum (4 mM) and calcium (6 mM), compared to bathing with lanthanum-free solution (control). The conductance reduction was 52% when calcium was removed from the control solution. Supported by morphological and physiological evidence, it appears that, under in vivo conditions, calcium ions may diffuse paracellularly from the haemolymph towards the extrapallial fluid and vice-versa across the septate junctions in the OME of A. cygnea. Permeability of the septate junctions depended proportionally on the calcium concentration in fluids.

Cytometric, morphologic and enzymatic characterisation of haemocytes in Anodonta cygnea

The haemocytes in bivalve mussels are involved in many processes such as lesion repair, shell repair, elimination of small particles and toxic substances. In Anodonta cygnea there are two categories of haemolymph cells, the granulocytes and hyalinocytes. Two groups of cells were identified by flow cytometry and morphological studies: one with larger size and granularity representing 75%, and another group of cells (25%) which were approximately half the size. The cytochemical reactions showed peroxidase activity in the larger cells and a weak prophenoloxidase activity in the smaller cells. These characteristics suggest that the most common haemocytes are granulocytes and hyalinocytes are less common. Enzymatic studies showed clear activities of few enzymes in different compartments of the mantle. Both haemocytes presented significant variations for alpha-manosidase and beta-glucurosidase activities depending on the acid or alkaline pH. Almost all were sensitive to the pH changes, mainly the beta-galactosidase in the haemolymph plasma. On the contrary, the same enzymatic analysis in the extrapallial elements showed more stabilised activities. The simulation of acidic and alkaline condition with the observation of significant morphological and enzymatic activity changes, allow us to speculate some functional role, mainly in the haemolymph elements. The granulocytes may be speculated to have intense involvement in the digestion of small residues with the formation of calcareous stores while the hyalinocytes are more responsible for the elimination of soluble cytotoxic compounds.

Freshwater bivalve shells as archival indicators of metal pollution from a copper-uranium mine in tropical northern Australia

Freshwater bivalves (Velesunio angasi) were sampled in 1996 from the Finniss River in tropical northern Australia at 10 sites a priori exposed and nonexposed to acid rock drainage (ARD), containing elevated metal concentrations, from the rehabilitated Rum Jungle copper-uranium mine. Secondary ion mass spectrometry (SIMS) was used to measure Cu, Mn, Zn, U, Ni, Co, Pb, and Fe/Ca ratios across the annual shell laminations of the longest-lived bivalves found at each site, with the aim of evaluating the ability of the shells to archive measured annual metal inputs and their temporal patterns. At sites not contaminated by ARD, relatively constant and similar (baseline) SIMS signals were found for all metals in the shell laminations of V. angasi, dating as far back as 1965. At sites contaminated by ARD, relatively constant, but variably elevated, SIMS signals were evident for Cu, Mn, Zn, Ni, and Co in the shell, which extended back to the end of rehabilitation (1986) only. Since rehabilitation, the temporal patterns of Cu, Zn, and Mn observed in the shells at the most contaminated sites reflected those of the measured annual dissolved loads in the surface waters. The average concentrations of Cu, Mn, Zn, Ni, and Co in the shells decreased (3-13-fold) with increasing distance downstream of the mine site, until concentrations characteristic of the noncontaminated sites were reached. This geographic pattern of decline in pollution signal in the shell with increasing distance downstream of the pollution input is consistent with the pattern established for water and sediment chemistry. Overall, the SIMS results support the proposition that the shells of V. angasi can be used as archival indicators of metal pollution in surface waters of the Finniss River over their lifetime.

The action of Cd, Cu, Cr, Zn, and Pb on fluid composition of Anodonta cygnea (L.): organic components

The heavy metals, Cd, Cu, Cr, Zn, and Pb, were used to incubate healthy specimens of the freshwater mussel species, Anodonta cygnea. Afterwards, their biological fluids, either haemolymph or extrapallial fluid were analyzed for the presence of several organic constituents, known to be important for biomineralization, such as proteins, glycosaminoglycans (GAGs) and glucosamine. Proteins were subjected to further study, namely through the total amino acid determination after acid hydrolysis. The most disturbing pollutants tested seem to be Pb, Zn, and Cr, which caused highly decreased overall compositions, namely with respect to protein, and glucosamine, in comparison to the control group. This suggests that this group contributes to a decrease of the metabolic activity, and thus mineralization, in the exposed animals.