A Galectin of Unique Domain Organization from Hemocytes of the Eastern Oyster (Crassostrea virginica) Is a Receptor for the Protistan Parasite Perkinsus marinus

Haplosporidium nelsoni and Perkinsus marinus occurrence in waters of Great Bay Estuary, New Hampshire

In Great Bay Estuary, New Hampshire, USA, Haplosporidium nelsoni and Perkinsus marinus are 2 active pathogens of the eastern oyster Crassostrea virginica (Gmelin), that cause MSX (multinucleated sphere with unknown affinity 'X') and dermo mortalities, respectively. Whereas studies have quantified infection intensities in oyster populations and determined whether these parasites exist in certain planktonic organisms, no studies thus far have examined both infectious agents simultaneously in water associated with areas that do and do not have oyster populations. As in other estuaries, both organisms are present in estuarine waters throughout the Bay, especially during June through November, when oysters are most active. Waters associated with oyster habitats had higher, more variable DNA concentrations from these pathogenic organisms than waters at a non-oyster site. This finding allows for enhanced understanding of disease-causing organisms in New England estuaries, where oyster restoration is a priority.

Determination, expression and characterization of an UDP-N-acetylglucosamine:α-1,3-D-mannoside β-1,2-N-acetylglucosaminyltransferase I (GnT-I) from the Pacific oyster, Crassostrea gigas

Molluscs are intermediate hosts for several parasites. The recognition processes, required to evade the host's immune response, depend on carbohydrates. Therefore, the investigation of mollusc glycosylation capacities is of high relevance to understand the interaction of parasites with their host. UDP-N-acetylglucosamine:α-1,3-D-mannoside β-1,2-N-acetylglucosaminyltransferase I (GnT-I) is the key enzyme for the biosynthesis of hybrid and complex type N-glycans catalysing the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to the α-1,3 Man antenna of Man5GlcNAc2. Thereby, the enzyme produces a suitable substrate for further enzymes, such as α-mannosidase II, GlcNAc-transferase II, galactosyltransferases or fucosyltransferases. The sequence of GnT- I from the Pacific oyster, Crassostrea gigas, was obtained by homology search using the corresponding human enzyme as the template. The obtained gene codes for a 445 amino acids long type II transmembrane glycoprotein and shared typical structural elements with enzymes from other species. The enzyme was expressed in insect cells and purified by immunoprecipitation using protein A/G-plus agarose beads linked to monoclonal His-tag antibodies. GnT-I activity was determined towards the substrates Man5-PA, MM-PA and GnM-PA. The enzyme displayed highest activity at pH 7.0 and 30 °C, using Man5-PA as the substrate. Divalent cations were indispensable for the enzyme, with highest activity at 40 mM Mn2+, while the addition of EDTA or Cu2+ abolished the activity completely. The activity was also reduced by the addition of UDP, UTP or galactose. In this study we present the identification, expression and biochemical characterization of the first molluscan UDP-N-acetylglucosamine:α-1,3-D-mannoside β-1,2-N-acetylglucosaminyltransferase I, GnT-I, from the Pacific oyster Crassostrea gigas.

Placental galectins: a subfamily of galectins lose the ability to bind β-galactosides with new structural features†

Galectins are a phylogenetically conserved family of soluble β-galactoside binding proteins. There are 16 different of galectins, each with a specific function determined by its distinct distribution and spatial structure. Galectin-13, galectin-14, and galectin-16 are distinct from other galectin members in that they are primarily found in placental tissue. These galectins, also referred to as placental galectins, play critical roles in regulating pregnancy-associated processes, such as placenta formation and maternal immune tolerance to the embedded embryo. The unique structural characteristics and the inability to bind lactose of placental galectins have recently received significant attention. This review primarily examines the novel structural features of placental galectins, which distinguish them from the classic galectins. Furthermore, it explores the correlation between these structural features and the loss of β-galactoside binding ability. In addition, the newly discovered functions of placental galectins in recent years are also summarized in our review. A detailed understanding of the roles of placental galectins may contribute to the discovery of new mechanisms causing numerous pregnancy diseases and enable the development of new diagnostic and therapeutic strategies for the treatment of these diseases, ultimately benefiting the health of mothers and offspring.

l-fucoside localization in the gills of the genus Takifugu and its possible implication in the parasitism of Heterobothrium okamotoi (Monogenea: Diclidophoridae)

BACKGROUND

The monogenean parasite Heterobothrium okamotoi only parasitizes the gills of Takifugu rubripes. In this study, we hypothesized that the carbohydrates contribute to high host specificity of H. okamotoi.

METHODS

T. rubripes, T. niphobles, T. snyderi, and T. pardalis were used for UEA I staining of the gills and an in vivo challenge test against H. okamotoi. To examine the effect of l-fucose, an in vitro detachment test was conducted using the host's gills. Additionally, fucosylated proteins were isolated from the membrane proteins of T. niphobles gills.

RESULTS

The location of l-fucoside and the infection dynamics in four species were correlated to some extent; H. okamotoi detached relatively quickly from T. niphobles possessing l-fucoside both on the surface of the gills and in certain types of cells, including mucus cells, but detached slowly from T. snyderi possessing l-fucoside in only certain types of cells, including mucus cells. Under the conditions examined, H. okamotoi exhibited minimal detachment from T. rubripes and T. pardalis, and l-fucoside was not detected. The significantly higher detachment rate of H. okamotoi from the host's gills incubated in l-fucose-containing medium compared with the controls suggests that l-fucose in the non-host gills induced detachment of H. okamotoi. Four fucosylated proteins, including mucin5AC-like, were identified as potential factors for the detachment of H. okamotoi.

CONCLUSIONS

Fucosylated proteins covering the surface of non-host gills might contribute to H. okamotoi detachment.

GENERAL SIGNIFICANCE

This research shows the possible involvement of oligosaccharides in the host specificity of monogenean parasites.

Expression and Characterization of a β-Galactosidase from the Pacific Oyster, Crassostrea gigas, and Evaluation of Strategies for Testing Substrate Specificity

β-Galactosidases (EC 3.2.1.23) are exoglycosidases that catalyze the cleavage of glycoconjugates with terminal β-D-galactose residues in β1,3-, β1,4- or β1,6-linkage. Although this family of exoglycosidases has been extensively studied in vertebrates, plants, yeast, and bacteria, little information is available for mollusks. Mollusks are a diverse and highly successful group of animals that play many different roles in their ecosystems, including filter feeders and detritivores. Here, the first β-galactosidase from the Pacific oyster, Crassostrea gigas was discovered, biochemically characterized, and compared to our previously characterized slug enzyme from Arion vulgaris (UniProt Ref. Nr.: A0A0B7AQJ9). Overall, the mussel enzyme showed similar biochemical parameters to the snail enzyme. The enzyme from C. gigas was most active in an acidic environment (pH 3.5) and at a reaction temperature of 50 °C. Optimal storage conditions were up to 37 °C. In contrast to the enzyme from A. vulgaris, the supplementation of cations (Ni2+, Co2+, Mn2+, Mg2+, Ca2+, Cu2+, Ba2+) increased the activity of the enzyme from C. gigas. Substrate specificity studies of the β-galactosidases from the mussel, C. gigas, and the slug, A. vulgaris, revealed activity towards terminal β1,3- and β1,4-linked galactose residues for both enzymes. Using the same substrates in labeled and unlabeled form, we were able to detect the effect of labeling on the β-galactosidase activity using MALDI-TOF MS, HPTLC, and HPLC. While lactose was cleaved by the enzymes in an unlabeled or labeled state, galacto-N-biose was not cleaved as soon as a 2-amino benzoic acid label was added. In this study we present the biochemical characterization of the first recombinantly expressed β-galactosidase from the Pacific oyster, C. gigas, and we compare different analytical methods for the determination of β-galactosidase activity using the enzyme from C. gigas and A. vulgaris.

Specification of hemocyte subpopulations based on immune-related activities and the production of the agglutinin MkC1qDC in the bivalve Modiolus kurilensis

Bivalves, such as Modiolus are used as indicator organisms to monitor the state of the marine environment. Even though hemocytes are known to play a key role in the adaptive and protective mechanisms of bivalves, these cells are poorly studied in horse-mussel Modiolus kurilensis. In this paper, we present classification of horse-mussel hemocytes based on their immune functions, including the production of specific immune-related molecules, as well as their morphological composition after isolation by density gradient centrifugation. An effective fractionation protocol was adapted to separate four hemocyte subpopulations with distinct morphofunctional profiles. First subpopulation consisted of small under-differentiated hemoblasts (2.20 ± 0.85%) with a bromodeoxyuridine positive nucleus, and did not show any immune reactivity. Second was represented by agranulocytes (24.11 ± 2.40%), with evenly filled cytoplasm containing a well-developed protein-synthesizing apparatus, polysomes, smooth endoplasmic reticulum and mitochondria, and positively stained for myeloperoxidase, acidic proteins, glycogen and neutral polysaccharides. Third subpopulation consisted of eosinophilic granulocytes (62.64 ± 9.32%) that contained the largest number of lysosomes, peroxisomes and vesicles with contents of different density, and showed the highest phosphatase, reactive oxygen species (ROS) and phagocytic activities. Lastly, fourth group, basophilic granulocytes (14.21 ± 0.34%), are main producers of lectin-like protein MkC1qDC, recently discovered in M. kurilensis and characterized by pronounced antibacterial and anticancer activity. These cells characterized by intracytoplasmic of the MkC1qDC localization, forming granule-like bodies visualized with specific antibody. Both granulocytes and agranulocytes showed phagocytic activity and ROS production, and these reactions were more pronounced for eosinophilic granulocytes, suggesting that this group is the key element of the cell-mediated immune response of M. kurilensis. Our results support a concept of bivalve's hemocyte specification with distinct phenotypes.

Perkinsus marinus in bioreactor: growth and a cost-reduced growth medium

Perkinsus marinus (Perkinsea) is an osmotrophic facultative intracellular marine protozoan responsible for "Dermo" disease in the eastern oyster, Crassostrea virginica. In 1993 in vitro culture of P. marinus was developed in the absence of host cells. Compared to most intracellular protozoan parasites, the availability of P. marinus to grow in the absence of host cells has provided the basis to explore its use as a heterologous expression system. As the genetic toolbox is becoming available, there is also the need for larger-scale cultivation and lower-cost media formulations. Here, we took an industrial approach to scaled-up growth from a small culture flask to bioreactors, which required developing new cultivation parameters, including aeration, mixing, pH, temperature control, and media formulation. Our approach also enabled more real-time data collection on growth. The bioreactor cultivation method showed similar or accelerated growth rates of P. marinus compared to culture in T-flasks. Redox measurements indicated sufficient oxygen availability throughout the cultivation. Replacing fetal bovine serum with chicken serum showed no differences in the growth rate and a 60% reduction in the medium cost. This study opens the door to furthering P. marinus as a valid heterologous expression system by showing the ability to grow in bioreactors.

ONE-SENTENCE SUMMARY

Perkinsus marinus, a microbial parasite of oysters that could be useful for developing vaccines for humans, has been shown to grow well in laboratory equipment that can be expanded to commercial scale using a less expensive growth formula than usual laboratory practice.

The sweet side of wound healing: galectins as promising therapeutic targets in hemostasis, inflammation, proliferation, and maturation/remodeling

INTRODUCTION

Understanding the molecular and cellular processes involved in skin wound healing may pave the way for the development of innovative approaches to transforming the identified natural effectors into therapeutic tools. Based on the extensive involvement of the ga(lactoside-binding)lectin family in (patho)physiological processes, it has been well established that galectins are involved in a wide range of cell-cell and cell-matrix interactions.

AREAS COVERED

In the present paper, we provide an overview of the biological role of galectins in repair and regeneration, focusing on four main phases (hemostasis, inflammation, proliferation, and maturation/remodeling) of skin repair using basic wound models (open excision vs. sutured incision).

EXPERT OPINION

The reported data make a strong case for directing further efforts to treat excisional and incisional wounds differently. Functions of galectins essentially result from their modular presentation. In fact, Gal-1 seems to play a role in the early phases of healing (anti-inflammatory) and wound contraction, Gal-3 accelerates re-epithelization and increases tensile strength (scar inductor). Galectins have also become subject of redesigning by engineering to optimize the activity. Clinically relevant, these new tools derived from the carbohydrate recognition domain platform may also prove helpful for other purposes, such as potent antibacterial agglutinins and opsonins.

Transcriptomic profiling of immune-associated molecules in the coelomocytes of lugworm Arenicola marina (Linnaeus, 1758)

Organization and functioning of immune system remain unevenly studied in different taxa of lophotrochozoan animals. We analyzed transcriptomic data on coelomocytes of the lugworm Arenicola marina (Linnaeus, 1758; Annelida, Polychaeta) to gain insights into the molecular mechanisms involved in polychaete immunity. Coelomocytes are specialized motile cells populating coelomic fluid of annelids, responsible for cellular defense reactions and providing humoral immune factors. The transcriptome was enriched with immune-related transcripts by challenging the cells in vitro with lipopolysaccharides of Escherichia coli and Zymosan from Saccharomyces cerevisiae. Our analysis revealed a multifaceted and complex internal defense system of the lugworm. A. marina possesses orthologs of proto-complement-like factors: six thioester-containing proteins, a complement-like receptor, and a MASP-related serine protease (MReM2). A. marina coelomocytes employ pattern-recognition receptors to detect pathogens and regulate immune responses. Among them, there are 18 Toll-like receptors and various putative lectin-like proteins with evolutionary conserved and taxa-specific domains. C-type lectins and a novel family of Gal-binding and CUB domains containing receptors were the most abundant in the transcriptome. The array of pore-forming proteins in the coelomocytes was surprisingly reduced compared to that of other invertebrate species. We characterized a set of conserved proteins metabolizing reactive oxygen species and nitric oxide and expanded the arsenal of potential antimicrobial peptides. Phenoloxidase activity in immune cells of lugworm is mediated only by laccase enzyme. The described repertoire of immune-associated molecules provides valuable candidates for further functional and comparative research on the immunity of annelids.

Investigations on the binding specificity of β-galactoside analogues with human galectin-1 using molecular dynamics simulations

Galectin-1 (Gal-1) is the first member of galectin family, which has a carbohydrate recognition domain, specifically binds towards β-galactoside containing oligosaccharides. Owing its association with carbohydrates, Gal-1 is involved in many biological processes such as cell signaling, adhesion and pathological pathways such as metastasis, apoptosis and increased tumour cell survival. The development of β-galactoside based inhibitors would help to control the Gal-1 expression. In the current study, we carried out molecular dynamics (MD) simulations to examine the structural and dynamic behaviour Gal-1-thiodigalactoside (TDG), Gal-1-lactobionic acid (LBA) and Gal-1-beta-(1→6)-galactobiose (G16G) complexes. The analysis of glycosidic torsional angles revealed that β-galactoside analogues TDG and LBA have a single binding mode (BM1) whereas G16G has two binding modes (BM1 and BM2) for interacting with Gal-1 protein. We have computed the binding free energies for the complexes Gal-1-TDG, Gal-1-LBA and Gal-1-G16G using MM/PBSA and are -6.45, -6.22 and -3.08 kcal/mol, respectively. This trend agrees well with experiments that the binding of Gal-1 with TDG is stronger than LBA. Further analysis revealed that the interactions due to direct and water-mediated hydrogen bonds play a significant role to the structural stability of the complexes. The result obtained from this study is useful to formulate a set of rules and derive pharmacophore-based features for designing inhibitors against galectin-1.Communicated by Ramaswamy H. Sarma.

Structural and evolutionary insights into the multidomain galectin from the red abalone Haliotis rufescens with specificity for sulfated glycans

Galectins are an evolutionarily ancient family of lectins characterized by their affinity for β-galactosides and a conserved binding site in the carbohydrate recognition domain (CRD). These lectins are involved in multiple physiological functions, including the recognition of glycans on the surface of viruses and bacteria. This feature supports their role in innate immune responses in marine mollusks. Here, we identified and characterized a galectin, from the mollusk Haliotis rufescens (named HrGal), with four CRDs that belong to the tandem-repeat type. HrGal was purified by affinity chromatography in a galactose-agarose resin and exhibited a molecular mass of 64.11 kDa determined by MALDI-TOF mass spectrometry. The identity of HrGal was verified by sequencing, confirming that it is a 555 amino acid protein with a mass of 63.86 kDa. This protein corresponds to a galectin reported in GenBank with accession number AHX26603. HrGal is stable in the presence of urea, reducing agents, and ions such as Cu²⁺ and Zn²⁺. The recombinant galectin (rHrGal) was purified from inclusion bodies in the presence of these ions. A theoretical model obtained with the AlphaFold server exhibits four non-identical CRDs, with a β sandwich folding and the representative motifs for binding β-galactosides. This allows us to classify HrGal within the tandem repeat galectin family. On the basis of a phylogenetic analysis, we found that the mollusk sequences form a monophyletic group of tetradomain galectins unrelated to vertebrate galectins. HrGal showed specificity for galactosides and glucosides but only the sulfated sugars heparin and ι-carrageenan inhibited its hemagglutinating activity with a minimum inhibitory concentration of 4 mM and 6.25 X 10^-5% respectively. The position of the sulfate groups seemed crucial for binding, both by carrageenans and heparin.

Bivalve Haemocyte Subpopulations: A Review

Bivalve molluscs stand out for their ecological success and their key role in the functioning of aquatic ecosystems, while also constituting a very valuable commercial resource. Both ecological success and production of bivalves depend on their effective immune defence function, in which haemocytes play a central role acting as both the undertaker of the cellular immunity and supplier of the humoral immunity. Bivalves have different types of haemocytes, which perform different functions. Hence, identification of cell subpopulations and their functional characterisation in immune responses is essential to fully understand the immune system in bivalves. Nowadays, there is not a unified nomenclature that applies to all bivalves. Characterisation of bivalve haemocyte subpopulations is often combined with 1) other multiple parameter assays to determine differences between cell types in immune-related physiological activities, such as phagocytosis, oxidative stress and apoptosis; and 2) immune response to different stressors such as pathogens, temperature, acidification and pollution. This review summarises the major and most recent findings in classification and functional characterisation of the main haemocyte types of bivalve molluscs.

Perkinsus marinus suppresses in vitro eastern oyster apoptosis via IAP-dependent and caspase-independent pathways involving TNFR, NF-kB, and oxidative pathway crosstalk

The protozoan parasite Perkinsus marinus causes Dermo disease in eastern oysters, Crassostrea virginica, and can suppress apoptosis of infected hemocytes using incompletely understood mechanisms. This study challenged hemocytes in vitro with P. marinus for 1 h in the presence or absence of caspase inhibitor Z-VAD-FMK or Inhibitor of Apoptosis protein (IAP) inhibitor GDC-0152. Hemocytes exposure to P. marinus significantly reduced granulocyte apoptosis, and pre-incubation with Z-VAD-FMK did not affect P. marinus-induced apoptosis suppression. Hemocyte pre-incubation with GDC-0152 prior to P. marinus challenge further reduced apoptosis of granulocytes with engulfed parasite, but not mitochondrial permeabilization. This suggests P. marinus-induced apoptosis suppression may be caspase-independent, affect an IAP-involved pathway, and occur downstream of mitochondrial permeabilization. P. marinus challenge stimulated hemocyte differential expression of oxidation-reduction, TNFR, and NF-kB pathways. WGCNA analysis of P. marinus expression in response to hemocyte exposure revealed correlated protease, kinase, and hydrolase expression that could contribute to P. marinus-induced apoptosis suppression.

Galectin, another lectin from Fenneropenaeus merguiensis contributed in shrimp immune defense

Numerous lectins act as pattern recognition receptors (PRRs) in the innate immune system of invertebrates. Here, a galectin (FmGal) was isolated from hemocytes of Fenneropenaeus merguiensis. FmGal contained one open reading frame encoding a peptide of 338 amino acids. The primary sequence of FmGal comprised a carbohydrate recognition domain with a specific galactose binding site. The FmGal transcripts were found mostly in hemocytes of healthy shrimp. The expression of FmGal was up-regulated upon challenge with Vibrio parahaemolyticus and white spot syndrome virus (WSSV). Gene-silencing with FmGal double-stranded RNA resulted in extreme down-regulation of FmGal. Knockdown with a co-injection of pathogens reduced the survival rate of shrimp. Recombinant protein of FmGal (rFmGal) required Ca²⁺ to agglutinate pathogenic bacteria and exhibited sugar-specificity to galactose, lactose, lipopolysaccharide (LPS) and lipoteichoic acid (LTA). The ELISA-validated binding of rFmGal revealed higher affinity to LTA than LPS. rFmGal did not exhibit antibacterial activity but could enhance the phagocytosis and encapsulation of pathogenic invaders by hemocytes. Encapsulation was suppressed by galactose and lactose. Moreover, rFmGal also promoted the in vivo clearance of V. parahaemolyticus. FmGal, a galectin in F. merguiensis, participated in shrimp immunity, functioning as a PRR which might be involved in certain cellular responses.

Mollusc N-glycosylation: Structures, Functions and Perspectives

Molluscs display a sophisticated N-glycan pattern on their proteins, which is, in terms of involved structural features, even more diverse than that of vertebrates. This review summarises the current knowledge of mollusc N-glycan structures, with a focus on the functional aspects of the corresponding glycoproteins. Furthermore, the potential of mollusc-derived biomolecules for medical applications is addressed, emphasising the importance of mollusc research.

Transcriptomic Response to Perkinsus marinus in Two Crassostrea Oysters Reveals Evolutionary Dynamics of Host-Parasite Interactions

Infectious disease outbreaks are causing widespread declines of marine invertebrates including corals, sea stars, shrimps, and molluscs. Dermo is a lethal infectious disease of the eastern oyster Crassostrea virginica caused by the protist Perkinsus marinus. The Pacific oyster Crassostrea gigas is resistant to Dermo due to differences in the host-parasite interaction that is not well understood. We compared transcriptomic responses to P. marinus challenge in the two oysters at early and late infection stages. Dynamic and orchestrated regulation of large sets of innate immune response genes were observed in both species with remarkably similar patterns for most orthologs, although responses in C. virginica were stronger, suggesting strong or over-reacting immune response could be a cause of host mortality. Between the two species, several key immune response gene families differed in their expansion, sequence variation and/or transcriptional response to P. marinus, reflecting evolutionary divergence in host-parasite interaction. Of note, significant upregulation of inhibitors of apoptosis (IAPs) was observed in resistant C. gigas but not in susceptible C. virginica, suggesting upregulation of IAPs is an active defense mechanism, not a passive response orchestrated by P. marinus. Compared with C. gigas, C. virginica exhibited greater expansion of toll-like receptors (TLRs) and positive selection in P. marinus responsive TLRs. The C1q domain containing proteins (C1qDCs) with the galactose-binding lectin domain that is involved in P. marinus recognition, were only present and significantly upregulated in C. virginica. These results point to previously undescribed differences in host defense genes between the two oyster species that may account for the difference in susceptibility, providing an expanded portrait of the evolutionary dynamics of host-parasite interaction in lophotrochozoans that lack adaptive immunity. Our findings suggest that C. virginica and P. marinus have a history of coevolution and the recent outbreaks may be due to increased virulence of the parasite.

Shotgun analysis to identify differences in protein expression between granulocytes and hyalinocytes of the European flat oyster Ostrea edulis

Recovery of wild populations of the European flat oyster Ostrea edulis is important for ecosystem health and conservation of this species, because native oyster populations have dramatically declined or disappeared in most European waters. Diseases have contributed to oyster decline and are important constrains for oyster recovery. Understanding oyster immune system should contribute to design effective strategies to fight oyster diseases. Haemocytes play a pivotal role in mollusc immune responses protecting from infection. Two main types of haemocytes, granulocytes and hyalinocytes, are distinguished in O. edulis. A study aiming to explore differential functions between both haemocyte types and, thus, to enrich the knowledge of Ostrea edulis immune system, was performed by comparing the proteome of the two haemolymph cell types, using a shotgun approach through liquid chromatography (LC) coupled to mass spectrometry (MS). Cells from oyster haemolymph were differentially separated by Percoll density gradient centrifugation. Shotgun LC-MS/MS performance allowed the identification of 145 proteins in hyalinocytes and 138 in the proteome of granulocytes. After a comparative analysis, 55 proteins with main roles in defence were identified, from which 28 were representative of granulocytes and 27 of hyalinocytes, plus 11 proteins shared by both cell types. Different proteins involved in signal transduction, apoptosis, oxidative response, processes related with the cytoskeleton and structure, recognition and wound healing were identified as representatives of each haemocyte type. Important signalling pathways in the immune response such as MAPK, Ras and NF-κβ seemed to be more relevant for granulocytes, while the Wnt signalling pathway, particularly relevant for wound healing, more relevant in hyalinocytes. The differences in proteins involved in recognition and in cytoskeleton and structure suggest differential specialisation in processes of phagocytosis and internalisation of pathogens between haemocyte types. Apoptosis seemed more active in granulocytes. The differences in proteins involved in oxidative response also suggest different redox processes in each cell type.

Development of the Myzozoan Aquatic Parasite Perkinsus marinus as A Versatile Experimental Genetic Model Organism

The phylum Perkinsozoa is an aquatic parasite lineage that has devastating effects on commercial and natural mollusc populations, and also comprises parasites of algae, fish and amphibians. They are related to dinoflagellates and apicomplexans and thus offer excellent genetic models for both parasitological and evolutionary studies. Genetic transformation was previously achieved for Perkinsus spp. but with few tools for transgene expression and limited selection efficacy. We sought to expand the power of experimental genetic tools for Perkinsus using P. marinus as a model. We constructed a modular plasmid assembly system for expression of multiple genes simultaneously. We developed efficient selection systems for three drugs, puromycin, bleomycin and blasticidin, that are effective in as little as three weeks. We developed eleven new promoters of variable expression strength. Furthermore, we identified that genomic integration of transgenes is predominantly via non-homologous recombination but with transgene fragmentation including deletion of some elements. To counter these dynamic processes, we show that bi-cistronic transcripts using the viral 2A peptides can couple selection to the maintenance of the expression of a transgene of interest. Collectively, these new tools and insights provide great new capacity to genetically modify and study Perkinsus as an aquatic parasite and evolutionary model.

Imitating evolution's tinkering by protein engineering reveals extension of human galectin-7 activity

Wild-type lectins have distinct types of modular design. As a step to explain the physiological importance of their special status, hypothesis-driven protein engineering is used to generate variants. Concerning adhesion/growth-regulatory galectins, non-covalently associated homodimers are commonly encountered in vertebrates. The homodimeric galectin-7 (Gal-7) is a multifunctional context-dependent modulator. Since the possibility of conversion from the homodimer to hybrids with other galectin domains, i.e. from Gal-1 and Gal-3, has recently been discovered, we designed Gal-7-based constructs, i.e. stable (covalently linked) homo- and heterodimers. They were produced and purified by affinity chromatography, and the sugar-binding activity of each lectin unit proven by calorimetry. Inspection of profiles of binding of labeled galectins to an array-like platform with various cell types, i.e. sections of murine epididymis and jejunum, and impact on neuroblastoma cell proliferation revealed no major difference between natural and artificial (stable) homodimers. When analyzing heterodimers, acquisition of altered properties was seen. Remarkably, binding properties and activity as effector can depend on the order of arrangement of lectin domains (from N- to C-termini) and on the linker length. After dissociation of the homodimer, the Gal-7 domain can build new functionally active hybrids with other partners. This study provides a clear direction for research on defining the full range of Gal-7 functionality and offers the perspective of testing applications for engineered heterodimers.

Fine polystyrene microplastics render immune responses more vulnerable to two veterinary antibiotics in a bivalve species

Living in close proximity to the sediment of coastal areas, bivalves may be exposed to veterinary antibiotic residuals and microplastics (MPs) simultaneously. However, the immunotoxic impacts of veterinary antibiotics remain unknown in bivalves, let alone their interactions with MPs. Therefore, the immune responses of two representative veterinary antibiotics, oxytetracycline and florfenicol, was investigated in a bivalve species, the blood clam (Tegillarca granosa). The effects of the copresence of MPs on the immune responses triggered by these antibiotics were also analyzed. Results showed that exposure to antibiotics investigated led to significant alteration in hematic parameters and reduction in lectin content in serum. In addition to inducing ROS production, aggravating lipid peroxidation and DNA damage, and suppressing the hemocyte viability, antibiotic treatments also downregulated the expression of immune- and detoxification-related genes but upregulated apoptosis-related Caspase-3. Furthermore, the toxic impacts of antibiotics were found to be significantly increased by the copresence of MPs.

Purification and partial characterization of carbohydrate-recognition protein C-type lectin from Hemifusus pugilinus

A mannose binding lectin (C-type lectin) was detected in a molluscan snail Hemifusus pugilinus, this lectin molecule was isolated and purified from the plasma using mannose-fixed sepharose CL-4B column affinity chromatography. The purified protein corresponds to the molecular weight of 118 kDa on an SDS-PAGE gel. The divalent cation-dependent nature of the H. pugilinus lectin (Hp-Lec) evidenced through pH and thermal stability analysis using Circular Dichroism (CD) and Surface Plasmon Resonance (SPR) respectively. Functional investigations of the Hp-Lec reveal a broad spectrum of bacterial agglutination activity against wide range of Gram-positive and Gram-negative bacterial strains. Furthermore, Hp-Lec displayed the haemo agglutination activity against vertebrate red blood cells (RBCs) and its titers were recorded. Excitingly, microbial virulent pathogens such as fungal strains tested against the purified Hp-Lec (25 and 50 μg/ml), which exhibits the effective antifungal activity against tested fungal pathogens such as Aspergillus niger and A. flavus.

Quadruple domain-containing galectin from marine invertebrate disk abalone (Haliotis discus discus): Molecular perspectives in early development, immune expression, and potent antiviral responses

Galectins are well-known β-galactoside-binding proteins, which play vital roles in innate immune responses of both vertebrates and invertebrates. However, knowledge regarding invertebrate galectins is still in its infancy. With the intention of filling the knowledge gap, here we identified a quadruple domain-containing galectin from marine invertebrate disk abalone, Haliotis discus discus (AbGalec), and characterized it. AbGalec consisted of four distinct carbohydrate-recognition domains (CRDs) and lacked a signal peptide. Expression analysis revealed AbGalec to be ubiquitously expressed in all the examined early embryonic stages of abalone, with highest expression in the 16-cell stage, suggesting the importance of AbGalec in early developmental processes. Tissue distribution analysis revealed the highest expression of AbGalec in abalone mantle, followed by that in gills and hemocytes. Immune challenge experiments revealed significant upregulation of AbGalec at 24 h and 48 h post injection (p.i.) with bacterial and viral components. These results suggested the possible involvement of AbGalec in host defense mechanisms. Polyinosinic: polycytidylic acid (Poly I:C) and viral hemorrhagic septicemia virus (VHSV) injections were capable of inducing AbGalec transcript expression more prominently than bacterial stimulants, thus providing evidence for its role in viral infections. We determined the virus-neutralizing ability of a quadruple domain-containing galectin for the first time, by analyzing the downregulation of VHSV transcripts during the overexpression of AbGalec. Significant downregulation of VHSV transcripts was observed after 24 h and 48 h of post infection. Collectively, our findings reveal the potent antiviral responses of molluscan quadruple domain-containing galectin, AbGalec, along with its involvement in innate immunity.

Effects of high stocking density on the galectin gene expression in noble scallop Chalmys nobilis under bacterial infection

High stocking densities have been shown to have adverse effects on the physiology of bivalves. The noble scallop Chlamys nobilis is one of the most important cultured shellfish in Southern China. However, the effects of scallop stocking density on its immunity is not well understood. In this context, this study was conducted to assess the effect of high stocking density on the galectin (an important protein in innate immunity) gene expression of C. nobilis during bacterial infection. A full-length galectin (CnGal) gene was cloned. The ORF of the CnGal cDNA encodes a predicted protein containing 549 aa with four CRDs and no signal peptide. Our results reveal that high stocking density in the scallop not only led to high mortality and slow growth, but also changed tissue distribution of the CnGal expression. The individuals from the high stocking density group exhibited more differences among tissues than those from the control group, but the highest expression were both recorded in hemolymph. After the Vibrio parahaeomlyticus challenge, the gene's expression levels were all significantly up-regulated in the hemolymph and gill, but the time up to peak was different between the two tissues. The findings of this study could fill a gap in knowledge about how high stocking density affect scallop immunity at the molecular level.

Galectin-mediated immune recognition: Opsonic roles with contrasting outcomes in selected shrimp and bivalve mollusk species

Galectins are a structurally conserved family of ß-galactoside-binding lectins characterized by a unique sequence motif in the carbohydrate recognition domain, and of wide taxonomic distribution, from fungi to mammals. Their biological functions, initially described as key to embryogenesis and early development via recognition of endogenous ("self") carbohydrate moieties, are currently understood as also encompassing tissue repair, cancer metastasis, angiogenesis, adipogenesis, and regulation of immune homeostasis. More recently, however, numerous studies have contributed to establish a new paradigm by revealing that galectins can also bind to exogenous ("non-self") glycans on the surface of potentially pathogenic virus, bacteria, and eukaryotic parasites, and function both as pathogen recognition receptors (PRRs) and effector factors in innate immunity. Our studies on a galectin from the kuruma shrimp Marsupenaeus japonicus (MjGal), revealed that it functions as a typical PRR. Expression of MjGal is upregulated by infectious challenge, and can recognize both Gram (+) and Gram (-) bacteria. MjGal also recognizes carbohydrates on the shrimp hemocyte surface, and can cross-link microbial pathogens to the hemocytes, promoting their phagocytosis and clearance from circulation. Therefore, MjGal contributes to the shrimp's immune defense against infectious challenge both as a PRR and effector factor. Our studies on galectins from the bivalve mollusks, however, have shown that although they can function in immune defense as MjGal, protistan parasites take advantage of the recognition roles of the host galectins, for successful attachment and host infection. We identified in the eastern oyster Crassostrea virginica two galectins (CvGal1 and CvGal2) that not only recognize a large variety of bacterial species, but also the protozoan parasite Perkinsus marinus. Like the shrimp MjGal, both oyster galectins function as opsonins, and promote parasite adhesion and phagocytosis. However, P. marinus survives intrahemocytic oxidative killing and proliferates, eventually causing systemic infection and death of the oyster host. In the softshell clam Mya arenaria we identified a galectin (MaGal1) that displays carbohydrate specificity and recognition properties for sympatric Perkinsus species (P. marinus and P. chesapeaki), that are different from CvGal1 and CvGal2. Our results suggest that although galectins from bivalves can function as PRRs, Perkinsus parasites have co-evolved with their hosts to subvert the galectins' immune functions for host infection by acquisition of carbohydrate-based mimicry.

Genome to phenome tools: In vivo and in vitro transfection of Crassostrea virginica hemocytes

The sequencing of the Crassostrea virginica genome has brought back the interest for gene delivery and editing methodologies. Here, we report the expression in oyster hemocytes of two heterologous expression vectors under the CMV promoter delivered with dendrimers. Expression was monitored using confocal microscopy, flow cytometry, and immunofluorescence assay. C. virginica hemocytes were able to express the green fluorescence protein and Crassostrea gigas vascular endothelial growth factor under CMV viral promoter both in vivo and in vitro. These results provide the bases for interrogating the genome and adapting genome editing methodologies.

Haplosporidian host:parasite interactions

The host:parasite interactions of the 3 serious haplosporidian pathogens of oysters, on which most information exists, are reviewed. They are Bonamia ostreae in Ostrea spp. and Crassostrea gigas; Bonamia exitiosa in Ostrea spp.; and Haplosporidium nelsoni in Crassostrea spp. Understanding the haemocytic response to pathogens is constrained by lack of information on haematopoiesis, haemocyte identity and development. Basal haplospridians in spot prawns are probably facultative parasites. H. nelsoni and a species infecting Haliotis iris in New Zealand (NZAP), which have large extracellular plasmodia that eject haplosporosomes or their contents, lyse surrounding cells and are essentially extracellular parasites. Bonamia spp. have small plasmodia that are phagocytosed, haplosporosomes are not ejected and they are intracellular obligate parasites. Phagocytosis by haemocytes is followed by formation of a parasitophorous vacuole, blocking of haemocyte lysosomal enzymes and the endolysosomal pathway. Reactive oxygen species (ROS) are blocked by antioxidants, and host cell apoptosis may occur. Unlike susceptible O. edulis, the destruction of B. ostreae by C. gigas may be due to higher haemolymph proteins, higher rates of granulocyte binding and phagocytosis, production of ROS, the presence of plasma β-glucosidase, antimicrobial peptides and higher levels of haemolymph and haemocyte enzymes. In B.exitiosa infection of Ostrea chilensis, cytoplasmic lipid bodies (LBs) containing lysosomal enzymes accumulate in host granulocytes and in B. exitiosa following phagocytosis. Their genesis and role in innate immunity and inflammation appears to be the same as in vertebrate granulocytes and macrophages, and other invertebrates. If so, they are probably the site of eicosanoid synthesis from arachidonic acid, and elevated numbers of LBs are probably indicative of haemocyte activation. It is probable that the molecular interaction, and role of LBs in the synthesis and storage of eicosanoids from arachidonic acid, is conserved in innate immunity in vertebrates and invertebrates. However, it seems likely that haplosporidians are more diverse than realized, and that there are many variations in host parasite interactions and life cycles.

Molecular characterization and biological function of a tandem-repeat galectin-9 in Qihe crucian carp Carassius auratus

Galectin-9, as one of the important PRRs in host, could initiate the immune defense responses through recognizing and binding PAMPs on the surface of invading microorganisms. In this study, a new galectin-9 cDNA was identified and characterized in Qihe crucian carp Carassius auratus (named as CaGal-9). The complete cDNA sequence of CaGal-9 was 1318 bp, with an open reading frame (ORF) of 963 bp encoding 320 amino acids. The predicted CaGal-9 protein contained two non-identical carbohydrate recognition domains (CRDs), which possessed the representative motifs H-NPR and WG-EER to bind with β-galactoside. Based on the RT-qPCR detection, CaGal-9 was ubiquitously expressed at mRNA level in various tested tissues, and predominately expressed in spleen. Upon Aeromonas hydrophila and poly I: C challenge, the expressions of CaGal-9 were remarkably up-regulated in liver, spleen, kidney and head kidney in a time-depended manner. The recombinant CaGal-9 (rCaGal-9), purified from Escherichia coli BL21 (DE3), exhibited strong binding ability with lipopolysaccharide (LPS), peptidoglycan (PGN) and β-Glucan, as well as the examined microorganisms including fungus, Gram-negative bacteria, and Gram-positive bacteria. With regard to the agglutinating activity of rCaGal-9, it could agglutinate erythrocytes of rabbit and crucian carp, and the examined microorganisms. Taken together, in this study, it was suggested that CaGal-9 could play an important role in immune defense against pathogenic microorganisms in C. auratus, which functions as an important PRR to recognize PAMPs and agglutinate pathogenic microorganisms.

N-Linked Surface Glycan Biosynthesis, Composition, Inhibition, and Function in Cnidarian-Dinoflagellate Symbiosis

The success of symbioses between cnidarian hosts (e.g., corals and sea anemones) and micro-algal symbionts hinges on the molecular interactions that govern the establishment and maintenance of intracellular mutualisms. As a fundamental component of innate immunity, glycan-lectin interactions impact the onset of marine endosymbioses, but our understanding of the effects of cell surface glycome composition on symbiosis establishment remains limited. In this study, we examined the canonical N-glycan biosynthesis pathway in the genome of the dinoflagellate symbiont Breviolum minutum (family Symbiodiniaceae) and found it to be conserved with the exception of the transferase GlcNAc-TII (MGAT2). Using coupled liquid chromatography-mass spectrometry (LC-MS/MS), we characterized the cell surface N-glycan content of B. minutum, providing the first insight into the molecular composition of surface glycans in dinoflagellates. We then used the biosynthesis inhibitors kifunensine and swainsonine to alter the glycan composition of B. minutum. Successful high-mannose enrichment via kifunensine treatment resulted in a significant decrease in colonization of the model sea anemone Aiptasia (Exaiptasia pallida) by B. minutum. Hybrid glycan enrichment via swainsonine treatment, however, could not be confirmed and did not impact colonization. We conclude that functional Golgi processing of N-glycans is critical for maintaining appropriate cell surface glycan composition and for ensuring colonization success by B. minutum.

Structure-function studies of galectin-14, an important effector molecule in embryology

The expression of prototype galectin-14 (Gal-14) in human placenta is higher than any other galectin, suggesting that it may play a role in fetal development and regulation of immune tolerance during pregnancy. Here, we solved the crystal structure of dimeric Gal-14 and found that its global fold is significantly different from that of other galectins with two β-strands (S5 and S6) extending from one monomer and contributing to the carbohydrate-binding domain of the other. The hemagglutination assay showed that this lectin could induce agglutination of chicken erythrocytes, even though lactose could not inhibit Gal-14-induced agglutination activity. Calorimetry indicates that lactose does not interact with this lectin. Compared to galectin-1, galectin-3, and galectin-8, Gal-14 has two key amino acids (a histidine and an arginine) in the normally conserved, canonical sugar-binding site, which are substituted by glutamine (Gln53) and histidine (His57), thus likely explaining why lactose binding to this lectin is very weak. Lactose was observed in the ligand-binding site of one Gal-14 structure, most likely because ligand binding is weak and crystals were allowed to grow over a long period of time in the presence of lactose. We also found that EGFP-tagged Gal-14 is primarily localized within the nucleus of different cell types. In addition, Gal-14 colocalized with c-Rel (a member of NF-κB family) in HeLa cells. These findings indicate that Gal-14 might regulate signal transduction pathways through NF-κB hubs. Overall, the present study provides impetus for further research into the function of Gal-14 in embryology.

Influence of protein (human galectin-3) design on aspects of lectin activity

The concept of biomedical significance of the functional pairing between tissue lectins and their glycoconjugate counterreceptors has reached the mainstream of research on the flow of biological information. A major challenge now is to identify the principles of structure–activity relationships that underlie specificity of recognition and the ensuing post-binding processes. Toward this end, we focus on a distinct feature on the side of the lectin, i.e. its architecture to present the carbohydrate recognition domain (CRD). Working with a multifunctional human lectin, i.e. galectin-3, as model, its CRD is used in protein engineering to build variants with different modular assembly. Hereby, it becomes possible to compare activity features of the natural design, i.e. CRD attached to an N-terminal tail, with those of homo- and heterodimers and the tail-free protein. Thermodynamics of binding disaccharides proved full activity of all proteins at very similar affinity. The following glycan array testing revealed maintained preferential contact formation with N-acetyllactosamine oligomers and histo-blood group ABH epitopes irrespective of variant design. The study of carbohydrate-inhibitable binding of the test panel disclosed up to qualitative cell-type-dependent differences in sections of fixed murine epididymis and especially jejunum. By probing topological aspects of binding, the susceptibility to inhibition by a tetravalent glycocluster was markedly different for the wild-type vs the homodimeric variant proteins. The results teach the salient lesson that protein design matters: the type of CRD presentation can have a profound bearing on whether basically suited oligosaccharides, which for example tested positively in an array, will become binding partners in situ. When lectin-glycoconjugate aggregates (lattices) are formed, their structural organization will depend on this parameter. Further testing (ga)lectin variants will thus be instrumental (i) to define the full range of impact of altering protein assembly and (ii) to explain why certain types of design have been favored during the course of evolution, besides opening biomedical perspectives for potential applications of the novel galectin forms.

Purification and Biochemical Characterization of Selected F-Type Lectins

The purification of fucose-binding lectins from the liver of striped bass (Morone saxatilis), a teleost fish, and the identification of a novel lectin sequence motif led to the identification of a new family of lectins, the F-type lectins (FTLs) (see overview of the FTL family in Chapter 23 ). Isolation and purification of these proteins from liver extracts of striped bass was accomplished by affinity chromatography and size exclusion, and their identification as FTLs, by direct Edman sequencing, and protein, transcript, and gene sequence analysis. The development of specific antibodies against the M. saxatilis FTL provided an additional tool for the identification of FTLs. These methods have been successfully used for the purification of the FTL family members from tissues and body fluids of various animal species. Production and characterization of FTLs has been facilitated by the expression of the recombinant proteins. In this chapter, the biochemical characterization of FTLs is focused on the analysis of their carbohydrate specificity.

A qPCR-Based Survey of Haplosporidium nelsoni and Perkinsus spp. in the Eastern Oyster, Crassostrea virginica in Maine, USA

Eastern oyster (Crassostrea virginica) aquaculture is increasingly playing a significant role in the state of Maine's (USA) coastal economy. Here, we conducted a qPCR-based survey for Haplosporidium nelsoni, Perkinsus marinus, and Perkinsus chesapeaki in C. virginica (n = 1440) from six Maine sites during the summer-fall of 2016 and 2017. In the absence of reported die-offs, our results indicated the continued presence of the three protozoan parasites in the six sites. The highest H. nelsoni qPCR-prevalence corresponded to Jack's Point and Prentiss Island (x=40 and 48% respectively), both located in the Damariscotta River Estuary. Jack's Point, Prentiss Island, New Meadows River, and Weskeag River recorded the highest qPCR-prevalence for P. marinus (32-39%). While the P. marinus qPCR-prevalence differed slightly for the years 2016 and 2017, P. chesapeaki qPCR-prevalence in 2016 was markedly lower than 2017 (<20% at all sites versus >60% at all sites for each of the years, respectively). Mean qPCR-prevalence values for P. chesapeaki over the two-year study were ≥40% for samples from Jack's Point (49%), Prentiss Island (44%), and New Meadows River (40%). This study highlights that large and sustained surveys for parasitic diseases are fundamental for decision making toward the management of the shellfish aquaculture industry, especially for having a baseline in the case that die-offs occur.

Identification and characterization of a novel galectin from the mud crab Scylla paramamosain

Galectins are a family of β-galactoside-binding lectins that play key roles in the invertebrate innate immunity system, but no galectin genes have been identified in the mud crab (Scylla paramamosain) so far. The present study is the first to clone a galectin gene (SpGal) from S. paramamosain, by the rapid amplification of cDNA ends technique based on expressed sequence tags. The full-length cDNA of SpGal was 3142 bp. Its open reading frame encoded a polypeptide of 280 amino acids containing a GLECT/Gal-bind lectin domain and a potential N-glycosylation site. The deduced amino acid sequence and multi-domain organization of SpGal were highly similar to those of invertebrate galectins, and phylogenetic analysis showed that SpGal was closely related to galectin isolated from Portunus trituberculatus. The mRNA transcripts of SpGal were found to be constitutively expressed in a wide range of tissues, with its expression level being higher in the hepatopancreas, gill, and hemocytes. The mRNA expression level of SpGal increased rapidly after the crabs were stimulated by Vibrio alginolyticus, and the maximum expression appeared at 6 h after the challenge. The lipopolysaccharide-binding ability of SpGal was dependent on its concentration, and it also exhibited agglutination activity with three Gram-negative (Aeromonas hydrophila, Chryseobacterium indologenes and Vibrio alginolyticus) and three Gram-positive (Bacillus aquimaris, Staphylococcus aureus and Micrococcus lysodeik) bacterial strains. In addition, hemagglutination activity with rabbit erythrocytes was observed in the absence of d-galactose. These results indicate that SpGal in S. paramamosain acts as a pattern recognition receptor to recognize a broad spectrum of microbes. The findings together indicate that SpGal plays an important role in the innate immune mechanisms of S. paramamosain against pathogenic infection.

Biochemical Characterization of Oyster and Clam Galectins: Selective Recognition of Carbohydrate Ligands on Host Hemocytes and Perkinsus Parasites

Both vertebrates and invertebrates display active innate immune mechanisms for defense against microbial infection, including diversified repertoires of soluble and cell-associated lectins that can effect recognition and binding to potential pathogens, and trigger downstream effector pathways that clear them from the host internal milieu. Galectins are widely distributed and highly conserved lectins that have key regulatory effects on both innate and adaptive immune responses. In addition, galectins can bind to exogenous (“non-self”) carbohydrates on the surface of bacteria, enveloped viruses, parasites, and fungi, and function as recognition receptors and effector factors in innate immunity. Like most invertebrates, eastern oysters (Crassostrea virginica) and softshell clams (Mya arenaria) can effectively respond to most immune challenges through soluble and hemocyte-associated lectins. The protozoan parasite Perkinsus marinus, however, can infect eastern oysters and cause “Dermo” disease, which is highly detrimental to both natural and farmed oyster populations. The sympatric Perkinsus chesapeaki, initially isolated from infected M. arenaria clams, can also be present in oysters, and there is little evidence of pathogenicity in either clams or oysters. In this review, we discuss selected observations from our studies on the mechanisms of Perkinsus recognition that are mediated by galectin-carbohydrate interactions. We identified in the oyster two galectins that we designated CvGal1 and CvGal2, which strongly recognize P. marinus trophozoites. In the clam we also identified galectin sequences, and focused on one (that we named MaGal1) that also recognizes Perkinsus species. Here we describe the biochemical characterization of CvGal1, CvGal2, and MaGal1 with focus on the detailed study of the carbohydrate specificity, and the glycosylated moieties on the surfaces of the oyster hemocytes and the two Perkinsus species (P. marinus and P. chesapeaki). Our goal is to gain further understanding of the biochemical basis for the interactions that lead to recognition and opsonization of the Perkinsus trophozoites by the bivalve hemocytes. These basic studies on the biology of host-parasite interactions may contribute to the development of novel intervention strategies for parasitic diseases of biomedical interest.

How galectins have become multifunctional proteins

Having identified glycans of cellular glycoconjugates as versatile molecular messages, their recognition by sugar receptors (lectins) is a fundamental mechanism within the flow of biological information. This type of molecular interplay is increasingly revealed to be involved in a wide range of (patho)physiological processes. To do so, it is a vital prerequisite that a lectin (and its expression) can develop more than a single skill, that is the general ability to bind glycans. By studying the example of vertebrate galectins as a model, a total of five relevant characteristics is disclosed: i) access to intra- and extracellular sites, ii) fine-tuned gene regulation (with evidence for co-regulation of counterreceptors) including the existence of variants due to alternative splicing or single nucleotide polymorphisms, iii) specificity to distinct glycans from the glycome with different molecular meaning, iv) binding capacity also to peptide motifs at different sites on the protein and v) diversity of modular architecture. They combine to endow these lectins with the capacity to serve as multi-purpose tools. Underscoring the arising broad-scale significance of tissue lectins, their numbers in terms of known families and group members have steadily grown by respective research that therefore unveiled a well-stocked toolbox. The generation of a network of (ga)lectins by evolutionary diversification affords the opportunity for additive/synergistic or antagonistic interplay in situ, an emerging aspect of (ga)lectin functionality. It warrants close scrutiny. The realization of the enormous potential of combinatorial permutations using the five listed features gives further efforts to understand the rules of functional glycomics/lectinomics a clear direction.

Galectins in Host-Pathogen Interactions: Structural, Functional and Evolutionary Aspects

Galectins are a family of ß-galactoside-binding lectins characterized by a unique sequence motif in the carbohydrate recognition domain, and evolutionary and structural conservation from fungi to invertebrates and vertebrates, including mammals. Their biological roles, initially understood as limited to recognition of endogenous ("self") carbohydrate ligands in embryogenesis and early development, dramatically expanded in later years by the discovery of their roles in tissue repair, cancer, adipogenesis, and regulation of immune homeostasis. In recent years, however, evidence has also accumulated to support the notion that galectins can bind ("non-self") glycans on the surface of potentially pathogenic microbes, and function as recognition and effector factors in innate immunity. Thus, this evidence has established a new paradigm by which galectins can function not only as pattern recognition receptors but also as effector factors, by binding to the microbial surface and inhibiting adhesion and/or entry into the host cell, directly killing the potential pathogen by disrupting its surface structures, or by promoting phagocytosis, encapsulation, autophagy, and pathogen clearance from circulation. Strikingly, some viruses, bacteria, and protistan parasites take advantage of the aforementioned recognition roles of the vector/host galectins, for successful attachment and invasion. These recent findings suggest that galectin-mediated innate immune recognition and effector mechanisms, which throughout evolution have remained effective for preventing or fighting viral, bacterial, and parasitic infection, have been "subverted" by certain pathogens by unique evolutionary adaptations of their surface glycome to gain host entry, and the acquisition of effective mechanisms to evade the host's immune responses.

The sugar code: letters and vocabulary, writers, editors and readers and biosignificance of functional glycan-lectin pairing

Ubiquitous occurrence in Nature, abundant presence at strategically important places such as the cell surface and dynamic shifts in their profile by diverse molecular switches qualifies the glycans to serve as versatile biochemical signals. However, their exceptional structural complexity often prevents one noting how simple the rules of objective-driven assembly of glycan-encoded messages are. This review is intended to provide a tutorial for a broad readership. The principles of why carbohydrates meet all demands to be the coding section of an information transfer system, and this at unsurpassed high density, are explained. Despite appearing to be a random assortment of sugars and their substitutions, seemingly subtle structural variations in glycan chains by a sophisticated enzymatic machinery have emerged to account for their specific biological meaning. Acting as 'readers' of glycan-encoded information, carbohydrate-specific receptors (lectins) are a means to turn the glycans' potential to serve as signals into a multitude of (patho)physiologically relevant responses. Once the far-reaching significance of this type of functional pairing has become clear, the various modes of spatial presentation of glycans and of carbohydrate recognition domains in lectins can be explored and rationalized. These discoveries are continuously revealing the intricacies of mutually adaptable routes to achieve essential selectivity and specificity. Equipped with these insights, readers will gain a fundamental understanding why carbohydrates form the third alphabet of life, joining the ranks of nucleotides and amino acids, and will also become aware of the importance of cellular communication via glycan-lectin recognition.

Differential proteomic profiles and characterizations between hyalinocytes and granulocytes in ivory shell Babylonia areolata

The haemocytes of the ivory shell, Babylonia areolata are classified by morphologic observation into the following types: hyalinocytes (H) and granulocytes (G). Haemocytes comprise diverse cell types with morphological and functional heterogene and play indispensable roles in immunological homeostasis of invertebrates. In the present study, two types of haemocytes were morphologically identified and separated as H and G by Percoll density gradient centrifugation. The differentially expressed proteins were investigated between H and G using mass spectrometry. The results showed that total quantitative proteins between H and G samples were 1644, the number of up-regulated proteins in G was 215, and the number of down-regulated proteins in G was 378. Among them, cathepsin, p38 MAPK, toll-interacting protein-like and beta-adrenergic receptor kinase 2-like were up-regulated in G; alpha-2-macroglobulin-like protein, C-type lectin, galectin-2-1, galectin-3, β-1,3-glucan-binding protein, ferritin, mega-hemocyanin, mucin-17-like, mucin-5AC-like and catalytic subunit of protein kinase A were down-regulated in G. The results showed that the most significantly enriched KEGG pathways were the pathways related to ribosome, phagosome, endocytosis, carbon metabolism, protein processing in endoplasmic reticulum and oxidative phosphorylation. For phagosome and endocytosis pathway, the number of down-regulation proteins in G was more than that of up-regulation proteins. For lysosome pathway, the number of up-regulation proteins in G was more than that of down-regulation proteins. These results suggested that two sub-population haemocytes perform the different immune functions in B. areolata.

Lacking catalase, a protistan parasite draws on its photosynthetic ancestry to complete an antioxidant repertoire with ascorbate peroxidase

Background

Antioxidative enzymes contribute to a parasite’s ability to counteract the host’s intracellular killing mechanisms. The facultative intracellular oyster parasite, Perkinsus marinus, a sister taxon to dinoflagellates and apicomplexans, is responsible for mortalities of oysters along the Atlantic coast of North America. Parasite trophozoites enter molluscan hemocytes by subverting the phagocytic response while inhibiting the typical respiratory burst. Because P. marinus lacks catalase, the mechanism(s) by which the parasite evade the toxic effects of hydrogen peroxide had remained unclear. We previously found that P. marinus displays an ascorbate-dependent peroxidase (APX) activity typical of photosynthetic eukaryotes. Like other alveolates, the evolutionary history of P. marinus includes multiple endosymbiotic events. The discovery of APX in P. marinus raised the questions: From which ancestral lineage is this APX derived, and what role does it play in the parasite’s life history?

Results

Purification of P. marinus cytosolic APX activity identified a 32 kDa protein. Amplification of parasite cDNA with oligonucleotides corresponding to peptides of the purified protein revealed two putative APX-encoding genes, designated PmAPX1 and PmAPX2. The predicted proteins are 93% identical, and PmAPX2 carries a 30 amino acid N-terminal extension relative to PmAPX1. The P. marinus APX proteins are similar to predicted APX proteins of dinoflagellates, and they more closely resemble chloroplastic than cytosolic APX enzymes of plants. Immunofluorescence for PmAPX1 and PmAPX2 shows that PmAPX1 is cytoplasmic, while PmAPX2 is localized to the periphery of the central vacuole. Three-dimensional modeling of the predicted proteins shows pronounced differences in surface charge of PmAPX1 and PmAPX2 in the vicinity of the aperture that provides access to the heme and active site.

Conclusions

PmAPX1 and PmAPX2 phylogenetic analysis suggests that they are derived from a plant ancestor. Plant ancestry is further supported by the presence of ascorbate synthesis genes in the P. marinus genome that are similar to those in plants. The localizations and 3D structures of the two APX isoforms suggest that APX fulfills multiple functions in P. marinus within two compartments. The possible role of APX in free-living and parasitic stages of the life history of P. marinus is discussed.

Electronic supplementary material

The online version of this article (10.1186/s12862-019-1465-5) contains supplementary material, which is available to authorized users.

How altering the modular architecture affects aspects of lectin activity: case study on human galectin-1

Discoveries on involvement of glycan-protein recognition in many (patho)physiological processes are directing attention to exploring the significance of a fundamental structural aspect of sugar receptors beyond glycan specificity, i.e., occurrence of distinct types of modular architecture. In order to trace clues for defining design-functionality relationships in human lectins, a lectin's structural unit has been used as source material for engineering custom-made variants of the wild-type protein. Their availability facilitates comparative analysis toward the stated aim. With adhesion/growth-regulatory human galectin-1 as example, the strategy of evaluating how changes of its design (here, from the homodimer of non-covalently associated domains to (i) linker-connected di- and tetramers and (ii) a galectin-3-like protein) affect activity is illustrated by using three assay systems of increasing degree of glycan complexity. Whereas calorimetry with two cognate disaccharides and array testing with 647 (glyco)compounds disclosed no major changes, galectin histochemical staining profiles of tissue sections that present natural glycome complexity revealed differences between wild-type and linker-connected homo-oligomers as well as between the galectin-3-like variant and wild-type galectin-3 for cell-type positivity, level of intensity at the same site and susceptibility for inhibition by a bivalent glycocompound. These results underscore the strength of the documented approach. Moreover, they give direction to proceed to (i) extending its application to other members of this lectin family, especially galectin-3 and (ii) then analyzing impact of architectural alterations on cell surface lattice formation and ensuing biosignaling systematically, considering the variants' potential for translational medicine.

Identification and characterisation of a novel small galectin in razor clam (Sinonovacula constricta) with multiple innate immune functions

Galectins are lectins possessing an evolutionarily conserved carbohydrate recognition domain (CRD) with affinity for β-galactoside. The key role played by innate immunity in invertebrates has recently become apparent. Herein, a full-length galectin (ScGal) was identified in razor clam (Sinonovacula constricta). The 528 bp open reading frame encodes a polypeptide of 176 amino acids with a single CRD and no signal peptide. ScGal mRNA transcripts were mainly expressed in hemolymph and gill, and were significantly up-regulated following bacterial challenge. Recombinant rScGal protein binds to and aggregates various bacteria, and has affinity for peptidoglycan, lipoteichoic acid and _d-galactose. The protein also stimulates hemocytes to phagocytose invading bacterial pathogens. ScGal is an important immune factor in innate immunity, and a small protein with multiple important functions.

Lectinology 4.0: Altering modular (ga)lectin display for functional analysis and biomedical applications

BACKGROUND

Recognition of glycans by lectins is emerging as (patho)physiologically broadly used mode of cellular information transfer. Whereas the direct ligand-receptor contact is often already thoroughly characterized, the functional relevance of aspects of architecture such as modular design and valence of lectins is less well defined.

SCOPE OF REVIEW

Following an introduction to modular lectin design, three levels of methodology are then reviewed that delineate lectin structure-activity relationships beyond glycan binding, with emphasis on domain shuffling.

MAJOR CONCLUSIONS

Engineering of variants by modular transplantation facilitates versatile Nature-inspired design switches and access to new combinations with translational potential, as exemplified for human adhesion/growth-regulatory galectins.

GENERAL SIGNIFICANCE

To gain an understanding of the functional significance of natural variations in quaternary structure and modular design within a protein family is a current challenge. Strategic application of methods of the described phases is a means to respond to this challenge.

From the raw bar to the bench: Bivalves as models for human health

Bivalves, from raw oysters to steamed clams, are popular choices among seafood lovers and once limited to the coastal areas. The rapid growth of the aquaculture industry and improvement in the preservation and transport of seafood have enabled them to be readily available anywhere in the world. Over the years, oysters, mussels, scallops, and clams have been the focus of research for improving the production, managing resources, and investigating basic biological and ecological questions. During this decade, an impressive amount of information using high-throughput genomic, transcriptomic and proteomic technologies has been produced in various classes of the Mollusca group, and it is anticipated that basic and applied research will significantly benefit from this resource. One aspect that is also taking momentum is the use of bivalves as a model system for human health. In this review, we highlight some of the aspects of the biology of bivalves that have direct implications in human health including the shell formation, stem cells and cell differentiation, the ability to fight opportunistic and specific pathogens in the absence of adaptive immunity, as source of alternative drugs, mucosal immunity and, microbiome turnover, toxicology, and cancer research. There is still a long way to go; however, the next time you order a dozen oysters at your favorite raw bar, think about a tasty model organism that will not only please your palate but also help unlock multiple aspects of molluscan biology and improve human health.

Molecular cloning and expression analysis of C-type lectin (RpCTL) in Manila clam Ruditapes philippinarum after lipopolysaccharide challenge

The Manila clam, Ruditapes philippinarum, is one of the most commercially important marine bivalves. C-type lectins (CTLs) are pattern recognition receptors (PRRs) that play important roles in the identification and elimination of pathogens by the innate immune system. In this study, a new CTL (RpCTL) was identified in the Manila clam, R. philippinarum. The full-length RpCTL cDNA is 802 bp, with an open reading frame of 591 bp, encoding 196 amino acids, including an N-terminal signal peptide and a carbohydrate recognition domain (CRD). RpCTL contains conserved CRD disulfide bonds involving four cysteine residues (Cys³⁰-Cys¹⁰⁴, Cys¹²⁴, and Cys¹³²), and the EPN (Glu⁹⁴-Pro⁹⁵-Asn⁹⁶) and WND (Trp¹¹⁹-Asn¹²⁰-Asp¹²¹) motifs. Quantitative reverse transcription (RT)-PCR detected RpCTL transcripts mainly in the gill, siphon, and hepatopancreas in three shell-color strains (zebra, white, and white-zebra strains) and two unselected populations of R. philippinarum, and the gene was highly expressed in the hepatopancreas after lipopolysaccharide treatment. Antimicrobial activity assays of recombinant RpCTL against both Gram-positive and Gram-negative bacteria showed that RpCTL inhibits microorganismal growth. In a survival test, RpCTL inhibited and killed Vibrio anguillarum in R. philippinarum. These results suggest that RpCTL participates in the pathogen identification process of R. philippinarum as a PRR and in its immune defense system.

Transcriptome analysis of air-breathing land slug, Incilaria fruhstorferi reveals functional insights into growth, immunity, and reproduction

Background

Incilaria (= Meghimatium) fruhstorferi is an air-breathing land slug found in restricted habitats of Japan, Taiwan and selected provinces of South Korea (Jeju, Chuncheon, Busan, and Deokjeokdo). The species is on a decline due to depletion of forest cover, predation by natural enemies, and collection. To facilitate the conservation of the species, it is important to decide on a number of traits related to growth, immunity and reproduction addressing fitness advantage of the species.

Results

The visceral mass transcriptome of I. fruhstorferi was enabled using the Illumina HiSeq 4000 sequencing platform. According to BUSCO (Benchmarking Universal Single-Copy Orthologs) method, the transcriptome was considered complete with 91.8% of ortholog genes present (Single: 70.7%; Duplicated: 21.1%). A total of 96.79% of the raw read sequences were processed as clean reads. TransDecoder identified 197,271 contigs that contained candidate-coding regions. Of a total of 50,230 unigenes, 34,470 (68.62% of the total unigenes) annotated to homologous proteins in the Protostome database (PANM-DB). The GO term and KEGG pathway analysis indicated genes involved in metabolism, phosphatidylinositol signalling system, aminobenzoate degradation, and T-cell receptor signalling pathway. Many genes associated with molluscan innate immunity were categorized under pathogen recognition receptor, TLR signalling pathway, MyD88 dependent pathway, endogenous ligands, immune effectors, antimicrobial peptides, apoptosis, and adaptation-related. The reproduction-associated unigenes showed homology to protein fem-1, spermatogenesis-associated protein, sperm associated antigen, and testis expressed sequences, among others. In addition, we identified key growth-related genes categorized under somatotrophic axis, muscle growth, chitinases and collagens. A total of 4822 Simple Sequence Repeats (SSRs) were also identified from the unigene sequences of I. fruhstorferi.

Conclusions

This is the first available genomic information for non-model land slug, I. fruhstorferi focusing on genes related to growth, immunity, and reproduction, with additional focus on microsatellites and repeating elements. The transcriptome provides access to greater number of traits of unknown relevance in the species that could be exploited for in-depth analyses of evolutionary plasticity and making informed choices during conservation planning. This would be appropriate for understanding the dynamics of the species on a priority basis considering the ecological, health, and social benefits.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5526-3) contains supplementary material, which is available to authorized users.

A Brief History of Charcot-Leyden Crystal Protein/Galectin-10 Research

Eosinophils are present in tissues, such as the respiratory tract, spleen, lymph nodes and blood vessels. The significant presence of eosinophils in these tissues are associated with various diseases, including asthma, allergies, acute myeloid leukemia, etc. Charcot-Leyden crystal protein/galectin-10 is overexpressed in eosinophils and has also been identified in basophils and macrophages. In human body, this protein could spontaneously form Charcot-Leyden crystal in lymphocytes or in the lysates of lymphocytes. At present, the role of Charcot-Leyden crystal protein/galectin-10 in lymphocytes is not fully understood. This review summarizes research progress on Charcot-Leyden crystal protein/galectin-10, with emphasis on its history, cellular distributions, relations to diseases, structures and ligand binding specificity.

Galactoside-binding lectin in Solen grandis as a pattern recognition receptor mediating opsonization

Galactoside-binding lectin (galectin) is a type of pathogen recognition molecule that occupies an important position in the invertebrate innate immunity system. Our previous study has identified a galectin gene in mollusk Solen grandis (SgGal-1) and illustrated its potential roles in innate immunity. By the functional study using recombinant protein and specific antibody, here, we confirmed the pivotal roles of SgGal-1 in immune defense of S. grandis. SgGal-1 protein was expressed in many tested tissues including gill, mantle, hepatopancreas and gonad, except hemocytes and muscle. The recombinant SgGal-1 (rSgGal-1) bound PGN and β-glucan instead of LPS in vitro, and it further caused significant agglutination of five different microbes, suggesting SgGal-1 served as a pattern recognition receptor (PRR) involved in immune defense of mollusk. Furthermore, SgGal-1 recruited hemocytes to encapsulate, which was blocked by anti-rSgGal-1 serum. In the meantime, rSgGal-1 as well as promoted the phagocytosis of hemocytes against Escherichia coli in vitro. All these results suggested that SgGal-1 in S. grandis not only acted as a PRR recognizing microbes but also directly participated in the process of immune opsonization to protect the host from pathogenic infection.

Identification of a novel galectin in Sinonovacula constricta and its role in recognition of Gram-negative bacteria

Galectins are soluble lectins that perform a pattern recognition function in invertebrate immunity and specifically recognise β-galactoside residues via conserved carbohydrate recognition domains. However, their function in bivalve molluscs has received little attention. Herein, a galectin (ScGal2) in razor clam (Sinonovacula constricta) consisting of a 507 bp open reading frame encoding a protein of 168 amino acids was identified and characterised. The protein includes a carbohydrate recognition domain (CRD), and several residues involved in dimerisation were found. ScGal2 mRNAs were mainly detected in hemolymph and liver, and expression was upregulated significantly following challenge with Vibrio anguillarum. Recombinant rScGal2 protein displayed strong agglutination activity toward Gram-negative bacteria, and flow cytometry revealed that ScGal2 strongly promoted phagocytosis in hemocytes. These results suggest that ScGal2 plays an indispensable role in innate immunity in razor clam, and likely participates in immune recognition and clearance processes.

Responses of an oyster host (Crassostrea virginica) and its protozoan parasite (Perkinsus marinus) to increasing air temperature

Background

Changes in climate are predicted to influence parasite and pathogen infection patterns in terrestrial and marine environments. Increases in temperature in particular may greatly alter biological processes, such as host-parasite interactions. For example, parasites could differentially benefit from increased reproduction and transmission or hosts could benefit from elevated immune responses that may mediate or even eliminate infections. In the southeastern United States, the Eastern oyster, Crassostrea virginica, is infected by the lethal protozoan parasite, Perkinsus marinus. Under field conditions, intertidal (air-exposed) oysters have been found to have significantly higher P. marinus infection intensity and marginally higher infection prevalence than subtidal (submerged) oysters. During summer, air temperatures are much warmer than water and this exposure of intertidal oysters to higher temperatures is a suggested mechanism for increased infection intensity.

Methods

We simulated intertidal exposure using controlled laboratory experiments to determine how host traits (survival and immune response) and parasite infection intensity will respond to elevated air temperature ranging from 27 °C to 53 °C during emersion at low tide. In Georgia, where our work was conducted, the average summer water temperature is 29 °C and the average maximum high air temperature in July is 33 °C (though oysters have been shown to survive at much higher air temperatures).

Results

Host survival declined as temperature increased, with a definitive drop-off between 39–43 °C. Negative effects of air temperature on host immune response (phagocytic activity) were detectable only at extremely high temperatures (47–50 °C) when hosts were suffering acute mortality. Parasite infection intensity peaked at 35 °C.

Discussion

Our results suggest that an increase in average summer air temperature to 35 °C or higher could affect oyster survival directly through temperature-related impacts in the short-term and indirectly through increased P. marinus infection intensity over the long-term.