Characterization and immunocytochemical localization of actin and fibronectin in haemocytes of the mussel Mytilus galloprovincialis

Short-term in vitro exposure of Pinctada imbricata's haemocytes to Quaternium-15: exploring physiological and cellular responses

Since the 2000s, the pearl oyster Pinctada imbricata (Röding, 1798) has become established along the transitional waterways of the "Capo Peloro Lagoon" natural reserve, where it is now abundant due to its adaptability to different hydrological, climatic, environmental, and pollution conditions. This study aims to evaluate haemocyte immune-mediated responses in vitro to quaternium-15, a common pollutant in aquatic ecosystems. Cell viability and phagocytosis activity decreased when exposed to 0.1 or 1mg/L of quaternium-15. Moreover, decreasing phagocytosis was confirmed by gene expression modulation of actin, involved in cytoskeleton rearrangement. Effects on oxidative stress-related genes were also assessed (Cat, MnSod, Zn/CuSod, GPx). The qPCR data revealed alterations in antioxidant responses through gene dose- and time-dependent modulation. This study presents insights into the physiological responses and cellular mechanisms of P. imbricata haemocytes to environmental stressors, indicating that this species is useful as a novel bioindicator for future toxicological studies.

Immunohistochemical Detection of Various Proteoglycans in the Extracellular Matrix of Zebra Mussels

Mussels have been used as animal models for studying ecotoxicology, biomineralization, and bio-adhesion for many years. Despite a wealth of studies on their shell matrix and byssus proteins, few studies have focused on the extracellular matrix molecules in mussel soft tissues. Extracellular matrix molecules may play important roles in biomineralization, immune reaction, and tissue homeostasis. In the present study, extracellular matrix and mineralization-related molecules in zebra mussel soft tissue were immunolocalized using well-characterized monoclonal antibodies. Our results demonstrate specific immunolocalization for collagen IV, fibronectin, and keratan sulfate in hemocytes; collagen IV in peripheral nerves; and aggrecan, link protein, and collagen XVIII in foot tissue. Laminin, decorin, and osteonectin were also broadly immunolocalized in mussel soft tissues. The distributions of these extracellular matrix molecules in mussel tissues are in line with the cell-mediated shell mineralization hypothesis, providing evidence for the molecules involved in the peripheral nervous system and byssus formation, and explaining the conservation of extracellular matrix molecules during evolution. These results further contribute to establishing zebra mussels as an attractive animal model in biomedical research.

RNA-seq analysis of the mantle transcriptome from Mytilus edulis during a seasonal spawning event in deep and shallow water culture sites on the northeast coast of Newfoundland, Canada

The blue mussel (Mytilus edulis) has global commercial and ecological importance both in wild and cultured conditions. However there is a qualitative and quantitative lack of knowledge of the molecular mechanisms associated with its reproductive physiology, especially with reference to environmental interactions. Here we initiated a transcriptomic analysis (RNA-sequencing (RNA-seq)) of the mantle from both sexes sampled during a seasonal spawning event and from two culture depths (shallow-5 m; deep- 15 m). Mantle libraries were produced from 3 males and 3 females sampled from each of two shallow sites and two deep sites for a total of 12 replicate male and 12 replicate female libraries (24 total libraries). Overall a total of 2.3 billion raw 100 base reads with an average of 96.5 million reads/library were obtained and assembled into 296,118 transcripts with an average length of 568 bp. Overall, 315 transcripts from male libraries and 25 from female libraries were found to be upregulated in deep water as compared to shallow (edgeR adjusted p value ≤ 0.05). Conversely, 126 transcripts from male libraries and 135 from female libraries were found to be significantly downregulated at the same depth. Thirteen transcripts were selected for qPCR validation based on importance in reproduction, antimicrobial defense and metabolism. Of these, 9 RNA-seq identified transcripts were shown by qPCR to be differentially expressed between groups: 2 were upregulated in deep compared with shallow water (dhx38, mt-co1), 2 were upregulated for female compared with male mantle (pias2, mapkap1) and 6 genes (fndc3a, acbd3, klhl10, ccnb3, armc4, mt-co1) showed to be upregulated in males compared to females. The majority of qPCR studied transcripts were identified as involved in gamete development based on the UniProt database. This study further characterizes the importance of the mantle transcriptome during reproductive activities of M. edulis.

In vitro toxicity testing in hemocytes of the marine mussel Mytilus galloprovincialis (L.) to uncover mechanisms of action of the water accommodated fraction (WAF) of a naphthenic North Sea crude oil without and with dispersant

Dispersants used in oil spills could result toxic to marine organisms and could influence the toxicity of oil compounds. The aim of this work was to uncover the mechanisms of action of the water accommodated fraction (WAF) of a naphthenic North Sea crude oil produced at 10, 15 and 20 °C without and with the dispersant Finasol OSR52 (WAF and WAFD, respectively) using hemocytes of the marine mussel Mytilus galloprovincialis. Primary cultures of hemocytes were exposed in glass-coated microplates to different WAF or WAFD dilutions (0.25, 2.5, 25, 50 and 100%) and to the dispersant alone at the same concentrations present in the WAFD dilutions (1.25, 12.5, 125, 250 and 500 mg/L). Of the two in vitro approaches tested, the second one was selected which involved exposure of hemocytes for 4 h to unfiltered WAF, WAFD and dispersant dilutions without cell culture media. WAF decreased hemocytes viability only at the highest dilution whereas WAFD and the dispersant alone were cytotoxic at the three highest concentrations. Temperature of production of WAF, WAFD and dispersant did not influence their cytotoxicity to hemocytes. WAF increased ROS production and MXR transport activity in hemocytes. Exposure to WAFD and dispersant increased ROS production, provoked plasma membrane and actin cytoskeleton disruption and decreased phagocytic activity. In conclusion, the dispersant tested was toxic to mussel hemocytes and it greatly increased the toxicity of WAFD. The present data could be useful for the environmental risk assessment of oil spills and their remediation strategies in the marine environment.

Flow cytometry and micro-Raman spectroscopy: Identification of hemocyte populations in the mussel Mytilus galloprovincialis (Bivalvia: Mytilidae) from Faro Lake and Tyrrhenian Sea (Sicily, Italy)

Immunological and structural characteristics of hemocyte populations in the mussel Mytilus galloprovincialis (Bivalvia: Mytilidae), going from two different Sicilian habitats (Faro Lake and Tyrrhenian sea), was investigated by means of two different techniques (flow cytometric and micro-Raman spectroscopy analyses). For this purpose, three hundred and sixty mussels Mytilus galloprovincialis were analyzed during November 2017. They were divided into two equal groups (triplicate sample) on the basis of the site of collection (n = 60 caught in Faro Lake - group A, and n = 60 caught in Tyrrhenian Sea - group B). Some several differences between the species of Faro Lake and Tyrrhenian Sea are observed and ascribed to the disruption of immune parameters induced by the variations of some qualitative water parameters (temperature, salinity, dissolved oxygen, pH, ammonium 10, free chlorine, total chlorine, total phosphate, orthofhosphate) recorded in the two habitats. This study is relevant for monitoring the conditions of the sea and Faro Lake, which is strongly influenced by the currents of the Tyrrhenian Sea. Faro lake is well known for the cultivation of mussels and this is part of a coastal habitat of particular interest, consisted of a peculiar biocenotic complex. Further, for the first time, significant different arrangement in the mussels cell structural organization was evidenced by simply following their highly reproducible Raman biomolecular signatures.

Microbial Diseases of Bivalve Mollusks: Infections, Immunology and Antimicrobial Defense

A variety of bivalve mollusks (phylum Mollusca, class Bivalvia) constitute a prominent commodity in fisheries and aquacultures, but are also crucial in order to preserve our ecosystem’s complexity and function. Bivalve mollusks, such as clams, mussels, oysters and scallops, are relevant bred species, and their global farming maintains a high incremental annual growth rate, representing a considerable proportion of the overall fishery activities. Bivalve mollusks are filter feeders; therefore by filtering a great quantity of water, they may bioaccumulate in their tissues a high number of microorganisms that can be considered infectious for humans and higher vertebrates. Moreover, since some pathogens are also able to infect bivalve mollusks, they are a threat for the entire mollusk farming industry. In consideration of the leading role in aquaculture and the growing financial importance of bivalve farming, much interest has been recently devoted to investigate the pathogenesis of infectious diseases of these mollusks in order to be prepared for public health emergencies and to avoid dreadful income losses. Several bacterial and viral pathogens will be described herein. Despite the minor complexity of the organization of the immune system of bivalves, compared to mammalian immune systems, a precise description of the different mechanisms that induce its activation and functioning is still missing. In the present review, a substantial consideration will be devoted in outlining the immune responses of bivalves and their repertoire of immune cells. Finally, we will focus on the description of antimicrobial peptides that have been identified and characterized in bivalve mollusks. Their structural and antimicrobial features are also of great interest for the biotechnology sector as antimicrobial templates to combat the increasing antibiotic-resistance of different pathogenic bacteria that plague the human population all over the world.

Identification of β integrin-like- and fibronectin-like proteins in the bivalve mollusk Mytilus trossulus

Integrins play a key role in the intermediation and coordination between cells and extracellular matrix components. In this study, we first determined the presence of the β integrin-like protein and its presumptive ligand, fibronectin-like protein, during development and in some adult tissues of the bivalve mollusc Mytilus trossulus. We found that β integrin-like protein expression correlated with the development and differentiation of the digestive system in larvae. Besides the presence of β integrin-like protein in the digestive epithelial larval cells, this protein was detected in the hemocytes and some adult tissues of M. trossulus. The fibronectin-like protein was detected firstly at the blastula stage and later, the FN-LP-immunoreactive cells were scattered in the trochophore larvae. The fibronectin-like protein was not expressed in the β integrin-positive cells of either the veliger stage larvae or the adult mussel tissues and the primary hemocyte cell culture. Despite the β integrin- and fibronectin-like proteins being expressed in different cell types of mussel larvae, we do not exclude the possibility of direct interaction between these two proteins during M. trossulus development or in adult tissues.

Flow cytometric characterization of hemocytes of the sunray venus clam Macrocallista nimbosa and influence of salinity variation

Sunray venus clam Macrocallista nimbosa is a native bivalve mollusc of Florida, USA, currently evaluated as a potential new aquaculture species. Very little is known about the physiology and hemocyte characteristics of this species. Bivalve hemocytes are generally involved in various physiological functions including nutrition, tissue repair, detoxification and immune defense. Understanding hemocytes of M. nimbosa and their response to environmental variations is crucial. In estuarine Florida areas, salinity is probably the most important factor potentially affecting clams physiology since wide variations can occur within few days. In the present work, using flow cytometry, hemocyte types and cellular parameters (oxidative activity, lysosomal content, phagocytosis capacity) were first characterized in sunray venus clams, in relation with endogenous variables (i.e., size, body weight, gender). Clams were then transferred from salinity 30 psu to 18, 21, 25, 30, 35 and 38 psu. After 7 days, impact of salinity variations was determined on hemocyte parameters, along with estimation of physiological status of clams (mortality, valve closure, filtration activity). Hemocytes of sunray venus clam appeared as a unique population, both in terms of morphology (FSC vs. SSC) and intracellular parameters, but displayed high inter-individual variability. Allometric relationship was only described for intracellular oxidative activity. Transfer of clams to 18 psu and, at lower extent, 21 psu resulted in valve closure, mortality and decreased filtration activity. Low salinities resulted in reduction of the number of circulating hemocytes, potentially reflecting infiltration in tissues as part of an inflammatory response or to optimize nutrient distribution. Low salinities also highly impacted hemocytes as depicted by increased cell and lysosomal compartment volumes, decreased phagocytosis capacity as well as increased oxidative stress and mortality. Salinity drops depress physiology and immune defense capacities of sunray venus clams, potentially threatening survival in case of concomitant pathogen encounter or secondary stress.

Effects of high temperature and exposure to air on mussel (Mytilus galloprovincialis, Lmk 1819) hemocyte phagocytosis: modulation of spreading and oxidative response

Hemocytes are a critical component of the mussel defense system and the present study aims at investigating their spreading and oxidative properties during phagocytosis under in vivo experimental stress conditions. The spreading ability was measured by an automated cell analyzer on the basis of the circularity, a parameter corresponding to the hemocyte roundness. The oxidative activity was investigated by micromethod assay, measuring the respiratory burst as expression of the fluorescence generated by the oxidation of specific probe. Following the application of high temperature and exposure to air, there was evidence of negative modulation of spreading and oxidative response, as revealed by a cell roundness increase and fluorescence generation decrease. Therefore, the fall of respiratory burst appeared as matched with the inhibition of hemocyte morphological activation, suggesting a potential depression of the phagocytosis process and confirming the application of the circularity parameter as potential stress marker, both in experimental and field studies.

Age related properties of the Adriatic clam Chamelea gallina (L. 1758) hemocytes

The clam Chamelea gallina (L 1758) represents an important shellfish resource along Mediterranean coasts and its progressive depletion has been ascribed both to the overexploitation of stocks and to environmental or anthropic stressors. In this context, the investigation on immune parameters could represent a valid approach to measure the clam homeostasis condition and its possible influence on population dynamics. On this basis, the innate immune system, mainly represented by hemocyte phagocytosis, was investigated in organisms of different size. The results indicated a better phagocytic response in larger clams, strictly related to a greater concentration of granulocytes. A such variation in hemolymph composition appeared not dependent on environmental or endogenous factors, but rather on clam aging.

Stress and immune responses in abalone: limitations in current knowledge and investigative methods based on other models

Increasing mariculture of abalone focuses attention on their immune and stress responses. For abalone, as well as many invertebrates, the function and relationship of these systems and how in vitro tests relate to them are not fully understood. This review focuses on research into the immune system and stress response conducted on abalone and on aspects that can be monitored in vitro. To fill the considerable knowledge gaps, we discuss work on other invertebrate taxa, concentrating on those closest to abalone, and making explicit the phylogenetic relations involved. The stress response appears to be very similar to that in vertebrates, but interpreting most immune responses remains problematic. Phylogeny must be considered: immune function tests derived from research into vertebrates or distantly related invertebrates should not be used in abalone until they have been validated in abalone by studies of susceptibility to pathogens. We suggest phagocytic activity of haemocytes and their efficiency in clearing bacteria are reliable parameters to measure, because they have been directly related to immune competency and are consistently depressed by stress. Carefully designed assays of antimicrobial activity may also be useful. Important aims of future research will be to investigate the relationship between growth, stress and robust immunity, and to develop tests that can be run on production animals, which accurately depict immune status.

Cytotoxicity of diatom-derived oxylipins in organisms belonging to different phyla

The cytotoxicity of several saturated and unsaturated marine diatom-derived aldehydes and an oxo-acid have been screened in vitro and in vivo against different organisms, such as bacteria, algae, fungi,echinoderms, molluscs and crustaceans. Conjugated unsaturated aldehydes like 2E,4E-decadienal, 2E,4E-octadienal,5E,7E-9-oxo-nonadienoic acid and 2E-decenal were active against bacteria and fungi and showed weak algicidal activity. By contrast, the saturated aldehyde decanal and the non-conjugated aldehyde 4Z-decenal had either low or no significant biological activity. In assays with oyster haemocytes, 2E,4E-decadienal exhibited a dose-dependent inhibition of cytoskeleton organisation, rate of phagocytosis and oxidative burst and a dose-dependent promotion of apoptosis. A maternal diatom diet that was rich in unsaturated aldehydes induced arrest of cell division and apoptotic cell degradation in copepod embryos and larvae,respectively. This wide spectrum of physiological pathologies reflects the potent cell toxicity of diatom-derived oxylipins, in relation to their non-specific chemical reactivity towards nucleophilic biomolecules. The cytotoxic activity is conserved across six phyla, from bacteria to crustaceans. Deregulation of cell homeostasis is supposed to induce the elimination of damaged cells through apoptosis. However, efficient protection mechanisms possibly exist in unicellular organisms. Experiments with a genetically modified yeast species exhibiting elevated membrane and/or cell wall permeability suggest that this protection can be related to the inability of the oxylipin compounds to enter the cell.

Comparative effects of cadmium, copper, paraquat and benzo[a]pyrene on the actin cytoskeleton and production of reactive oxygen species (ROS) in mussel haemocytes

The immune defence of mussels is comprised of cell-mediated and humoral mechanisms, in which haemocytes or blood cells play a key role. Environmental pollutants such as metallic and organic xenobiotics exert immunotoxical effects on aquatic organisms. Some of these xenobiotics are known to give rise to highly reactive oxygen species (ROS), thereby leading to oxidative damage to tissue macromolecules including DNA, proteins and lipids. Previously we have detected enhancement of ROS production together with severe alterations in the actin cytoskeleton after exposure of mussel haemocytes to the carcinogenic polycyclic aromatic hydrocarbon benzo[a]pyrene (b[a]p). In a similar way, cadmium is also known to cause disruption of the actin cytoskeleton in mussel haemocytes, however it is not known whether this effect occurs by direct action or through ROS production. The aim of the present study was to decipher whether cytoskeletal alterations caused by Cd in mussel haemocytes are linked to increased ROS production. ROS-producing model compounds copper (Cu), paraquat and b[a]p were used in parallel experiments for comparative purposes. In all contaminant exposure experiments actin cytoskeleton appeared damaged. On the other hand, ROS production was increased in paraquat and b[a]p exposure experiments but decreased in haemocytes exposed to Cu while no significant effects were detected in Cd exposure experiments. In conclusion, it appears that deleterious effects of Cu and Cd on the integrity of the actin cytoskeleton of haemocytes are not directly linked to ROS production, at least at the exposure conditions used in the present study.

Phagocyte spreading and phagocytosis in the compound ascidian Botryllus schlosseri: evidence for an integrin-like, RGD-dependent recognition mechanism

The involvement of integrins in phagocyte spreading and phagocytosis was investigated in the compound ascidian Botryllus schlosseri. The number of spreading cells was significantly reduced when adhesion occurred in the presence of the tetrapeptide Arg--Gly--Asp--Ser (RGDS), but not of Arg--Gly--Glu--Ser (RGES) indicating the involvement of RGD-mediated adhesion mechanisms in phagocyte spreading. The significant decrease of the fraction of spreading cells in the presence of Botryllus blood plasma suggests the presence of RGD-containing molecules in the blood of our species. The increase in the same index when blood plasma-coated slides as well as fibrinogen- and fibronectin-coated coverslips were used, fits with the above hypothesis. Adhesion in the presence of RGDS leads to a consistent alteration of the actin cytoskeleton, in agreement with the known role of integrin adhesion in microfilament organization. Phagocytosis was greatly reduced by RGDS in the incubation medium, but not by RGES, and was significantly increased by coating yeast cells with fibronectin or blood plasma. Both spreading and phagocytic capability were severely inhibited by wortmannin, suggesting the importance of phosphatidylinositol-3-kinase in integrin-mediated signal transduction in ascidians.

Air exposure and functionality of Chamelea gallina haemocytes: effects on haematocrit, adhesion, phagocytosis and enzyme contents

The Venus clam Chamelea gallina is fairly common along the western coasts of the Adriatic and is subjected to intense fishing. Since over the last 20 years extensive hypoxic and anoxic conditions have repeatedly damaged this natural resource, we decided to study the effects of anoxic stress on the functionality of clam haemocytes and the consequences on immune responses. Clams, exposed to air, close their valves and tissues become anoxic and metabolism processes switch to anaerobiosis. In these conditions, a significant decrease in the haematocrit value and in the percentage of acid phosphatase-positive haemocytes was observed, while the number of cells with beta-glucuronidase significantly increased after day 1. The above indices generally returned to control values when clams were re-immersed in seawater after 1 day of treatment. Clams exposed to air for 2 days and then re-immersed, attempted to recover in the subsequent 3 days. Animals had fully recovered on day 4. Three-day-exposed clams did not recover. Phagocytic and adhesion indices decreased significantly after the first day of air exposure. The change in frequency of three types of circulating cells (spreading, round, apoptotic) was also monitored.

Improved attachment and spreading in primary cell cultures of the eastern oyster, Crassostrea virginica

At present, establishment of a cell line from bivalve molluscs has been unsuccessful, and in vitro work is limited to primary cell cultures. We sought to improve attachment and spreading of cells of the eastern oyster, Crassostrea virginica, to aid primary cultures and to assist development of a bivalve cell line. Our objectives were to examine the effects of substrate on ventricle cell viability, attachment, and spreading by testing of collagen I, collagen IV, fibronectin, laminin, poly-D-lysine, and two types of uncoated tissue culture plates (Falcon and Corning). Experiments were conducted by incubating cells with the various substrates for 24 h and 5 d. An assay with a tetrazolium compound (MTS) was used to estimate cell numbers based on metabolic activity. Although differences in MTS assay values for substrate effect on cell viability were detected at 24 h and at 5 d (P > 0.0001), these were attributed to variations in metabolic activity due to different levels of attachment and spreading among treatments. Differences among treatments were detected in attachment and spreading at 24 h and 5 d (for all, P > 0.0001). At 24 h, poly-D-lysine induced the highest levels of attachment and spreading; no other factor performed better than the uncoated Falcon substrate, and collagen I performed most poorly. At 5 d, poly-D-lysine and the uncoated Corning substrate induced significantly higher levels of attachment and spreading than did the uncoated Falcons substrate, and collagen I performed most poorly. From these results, poly-D-lysine best promoted cell attachment and spreading. Fibronectin (at 24 h) and laminin (at 5 d) warrant further study. Along with improvements in medium composition, future work should involve screening of other attachment factors and combinations of factors, including those of bivalve origin.

Characterization of monoclonal antibodies against cell wall epitopes of the insect pathogenic fungus, Nomuraea rileyi: differential binding to fungal surfaces and cross-reactivity with host hemocytes and basement membrane components

Monoclonal antibodies (MAbs) were generated against epitopes on yeast-like hyphal bodies and hyphae of the entomopathogenic hyphomycete, Nomuraea rileyi. Two MAbs (4C10, 2H4) bind to epitopes common to both hyphal bodies and hyphae, whereas MAb 4E9 binds only to hyphal surfaces. 4C10 and 2H4 appear to be directed towards carbohydrate portions of cell surface mannoproteins, as evidenced by similarities in staining patterns between these MAbs and Concanavalin A on Western blots of N. rileyi cell wall extracts. These MAbs cross-react with antigens on blastospore and hyphal surfaces of two other entomopathogenic fungi, Beauveria bassiana and Paecilomyces farinosus in fluorescence microscopy assays, but do not cross-react with a non-entomopathogenic strain of Candida albicans or with Saccharomyces cerevisiae yeasts. MAb 4C10 also cross-reacts with immunocompetent granular hemocytes from Spodoptera exigua (beet armyworm) and Trichoplusia ni (cabbage looper) larvae and with S. exigua plasmatocytes. Electron microscopy revealed that this MAb binds to a component in cytoplasmic granules in the hemocytes, and that surface labeling may be due to the release of this MAb-positive component upon degranulation. MAb 2H4 does not cross-react with granular hemocytes, but does bind to plasmatocytes and hemocytes that tightly adhere to the substrate in monolayer assays. Additionally, MAb 4C10 specifically labels a basement membrane epitope on S. exigua fat body, suggesting that this antibody binds to mannose residues on extracellular matrix glycoproteins. Cross-reactivity of these N. rileyi MAbs with insect hemocyte and tissue components indicates that fungal surface epitopes can mimic host surface molecules, which could explain why N. rileyi hyphal bodies are not recognized by granulocytes and are able to circulate freely in the hemolymph without binding to basement membranes lining the hemocoel.

The effects of copper on actin and fibronectin organization in Mytilus galloprovincialis haemocytes

The effects of copper on actin and fibronectin organization in Mytilus galloprovincialis haemocytes were studied. The Cu2+ exposure of mussels caused severe perturbations in haemocyte actin and fibronectin organization with respect to non-exposed organisms. Cytoskeletal actin was analysed by indirect immunofluorescence, using an antitotal actin monoclonal antibody, and by rhodamine-conjugated phalloidin. The majority of haemocytes from Cu(2+)-exposed mussels displayed a round morphology, with short and blunt filopodia; they lacked the polarized phenotype which was typical in control samples. The cytoskeleton alteration, more evident after phalloidin staining, resulted in the disappearance of filamentous actin. The actin cortical meshwork also appeared disorganized. The cytoskeletal morphology studied by transmission electron microscopy after negative staining of Triton X-100-treated haemocytes confirmed these observations. The structural organization of actin when analysed by Western blotting showed a larger number of Triton-soluble actin pools in treated mussel haemocytes. Fibronectin was studied by indirect immunofluorescence using a polyclonal antiserum directed against mussel fibronectin. In treated mussels, fibronectin appeared to be strongly disorganized and its levels decreased in both haemocytes and haemolymph. The mechanism(s) of the copper-induced alterations on actin and fibronectin organization in mussel immunocytes is discussed.