Immunohistochemical studies on the distribution and the function of the D-galactose-specific lectins in the sponge Axinella polypoides (Schmidt)

An Update of Lectins from Marine Organisms: Characterization, Extraction Methodology, and Potential Biofunctional Applications

Lectins are a unique group of nonimmune carbohydrate-binding proteins or glycoproteins that exhibit specific and reversible carbohydrate-binding activity in a non-catalytic manner. Lectins have diverse sources and are classified according to their origins, such as plant lectins, animal lectins, and fish lectins. Marine organisms including fish, crustaceans, and mollusks produce a myriad of lectins, including rhamnose binding lectins (RBL), fucose-binding lectins (FTL), mannose-binding lectin, galectins, galactose binding lectins, and C-type lectins. The widely used method of extracting lectins from marine samples is a simple two-step process employing a polar salt solution and purification by column chromatography. Lectins exert several immunomodulatory functions, including pathogen recognition, inflammatory reactions, participating in various hemocyte functions (e.g., agglutination), phagocytic reactions, among others. Lectins can also control cell proliferation, protein folding, RNA splicing, and trafficking of molecules. Due to their reported biological and pharmaceutical activities, lectins have attracted the attention of scientists and industries (i.e., food, biomedical, and pharmaceutical industries). Therefore, this review aims to update current information on lectins from marine organisms, their characterization, extraction, and biofunctionalities.

Transdifferentiation and mesenchymal-to-epithelial transition during regeneration in Demospongiae (Porifera)

Origin and early evolution of regeneration mechanisms remain among the most pressing questions in animal regeneration biology. Porifera have exceptional regenerative capacities and, as early Metazoan lineage, are a promising model for studying evolutionary aspects of regeneration. Here, we focus on reparative regeneration of the body wall in the Mediterranean demosponge Aplysina cavernicola. The epithelialization of the wound surface is completed within 2 days, and the wound is completely healed within 2 weeks. The regeneration is accompanied with the formation of a mass of undifferentiated cells (blastema), which consists of archaeocytes, dedifferentiated choanocytes, anucleated amoebocytes, and differentiated spherulous cells. The main mechanisms of A. cavernicola regeneration are cell dedifferentiation with active migration and subsequent redifferentiation or transdifferentiation of polypotent cells through the mesenchymal-to-epithelial transformation. The main cell sources of the regeneration are archaeocytes and choanocytes. At early stages of the regeneration, the blastema almost devoid of cell proliferation, but after 24 hr postoperation (hpo) and up to 72 hpo numerous DNA-synthesizing cells appear there. In contrast to intact tissues, where vast majority of DNA-synthesizing cells are choanocytes, all 5-ethynyl-2'-deoxyuridine-labeled cells in the blastema are mesohyl cells. Intact tissues, distant from the wound, retains intact level of cell proliferation during whole regeneration process. For the first time, the apoptosis was studied during the regeneration of sponges. Two waves of apoptosis were detected during A. cavernicola regeneration: The first wave at 6-12 hpo and the second wave at 48-72 hpo.

Porifera Lectins: Diversity, Physiological Roles and Biotechnological Potential

An overview on the diversity of 39 lectins from the phylum Porifera is presented, including 38 lectins, which were identified from the class of demosponges, and one lectin from the class of hexactinellida. Their purification from crude extracts was mainly performed by using affinity chromatography and gel filtration techniques. Other protocols were also developed in order to collect and study sponge lectins, including screening of sponge genomes and expression in heterologous bacterial systems. The characterization of the lectins was performed by Edman degradation or mass spectrometry. Regarding their physiological roles, sponge lectins showed to be involved in morphogenesis and cell interaction, biomineralization and spiculogenesis, as well as host defense mechanisms and potentially in the association between the sponge and its microorganisms. In addition, these lectins exhibited a broad range of bioactivities, including modulation of inflammatory response, antimicrobial and cytotoxic activities, as well as anticancer and neuromodulatory activity. In view of their potential pharmacological applications, sponge lectins constitute promising molecules of biotechnological interest.

Biological activities of ACL-I and physicochemical properties of ACL-II, lectins isolated from the marine sponge Axinella corrugata

Lectin II from the marine sponge Axinella corrugata (ACL-II) was purified by affinity chromatography on rabbit erythrocytic stroma incorporated into a polyacrylamide gel, followed by gel filtration on Ultrogel AcA 44 column. Purified ACL-II is a lectin with an Mr of 80 kDa and 78 kDa, estimated by SDS-PAGE and by FPLC on Superose 12 HR column, respectively. ACL-II mainly agglutinates native rabbit erythrocytes and this hemagglutinating activity is independent of Ca(2+), Mg(2+) and Mn(2+), but is inhibited by d-galactose, chitin and N-acetyl derivatives, with the exception of GalNAc. ACL-II is stable for up to 65 °C for 30 min, with a better stability at a pH range of 2 to 6. In contrast, ACL-I displays a strong mitogenic and cytotoxic effect.

Immunohistochemical localization of an N-acetyl amino-carbohydrate specific lectin (ACL-I) of the marine sponge Axinella corrugata

The N-acetyl amino-carbohydrate specific lectin (ACL-I) was previously identified and purified by us from the marine sponge Axinella corrugata (phylum Porifera, class Demospongiae). The distribution of the specific lectin within the tissue of the sponge was studied by bright-field optical microscopy immunohistochemistry in order to better understand its physiological role in the sponge. Polyclonal antibodies were raised against purified ACL-I in mice and tested by Western blot technique. The immunohistochemical analysis of ACL-I in cross sections of A. corrugata showed that this lectin is found inside the denominated spherulous cells, which contain vesicles that store the lectin. Some evidence is shown that ACL-I might also be present in the extracellular matrix. It was not possible to demonstrate by the immunohistochemical technique if ACL-I is colocalized in both the plasma membrane and in the cytoplasm of the spherulous cells.

Cellular localization of debromohymenialdisine and hymenialdisine in the marine sponge Axinella sp. using a newly developed cell purification protocol

Sponges (Porifera), as the best known source of bioactive marine natural products in metazoans, play a significant role in marine drug discovery and development. As sessile filter-feeding animals, a considerable portion of the sponge biomass can be made of endosymbiotic and associated microorganisms. Understanding the cellular origin of targeted bioactive compounds from sponges is therefore important not only for providing chemotaxonomic information but also for defining the bioactive production strategy in terms of sponge aquaculture, cell culture, or fermentation of associated bacteria. The two alkaloids debromohymenialdisine (DBH) and hymenialdisine (HD), which are cyclin-dependent kinase inhibitors with pharmacological activities for treating osteoarthritis and Alzheimer's disease, have been isolated from the sponge Axinella sp. In this study, the cellular localization of these two alkaloids was determined through the quantification of these alkaloids in different cell fractions by high-performance liquid chromatography (HPLC). First, using a differential centrifugation method, the dissociated cells were separated into different groups according to their sizes. The two bioactive alkaloids were mainly found in sponge cells obtained from low-speed centrifugation. Further cell purifications were accomplished by a newly developed multi-step protocol. Four enriched cell fractions (C1, C2, C3, and C4) were obtained and subjected to light and transmission electron microscopy, cytochemical staining, and HPLC quantification. Compared to the low concentrations in other cell fractions, DBH and HD accounted for 10.9% and 6.1%, respectively, of dry weight in the C1 fraction. Using the morphological characteristics and cytochemical staining results, cells in the C1 fraction were speculated to be spherulous cells. This result shows that DBH and HD in Axinella sp. are located in sponge cells and mostly stored in spherulous cells.

Mechanical adaptability of a sponge extracellular matrix: evidence for cellular control of mesohyl stiffness in Chondrosia reniformisNardo

The marine sponge Chondrosia reniformis Nardo consists largely of a collagenous tissue, the mesohyl, which confers a cartilaginous consistency on the whole animal. This investigation was prompted by the incidental observation that, despite a paucity of potentially contractile elements in the mesohyl, intact C. reniformis stiffen noticeably when touched. By measuring the deflection under gravity of beam-shaped tissue samples, it was demonstrated that the flexural stiffness of the mesohyl is altered by treatments that influence cellular activities, including [Ca2+]manipulation, inorganic and organic calcium channel-blockers and cell membrane disrupters, and that it is also sensitive to extracts of C. reniformis tissue that have been repeatedly frozen then thawed. Since the membrane disrupters and tissue extracts cause marked stiffening of mesohyl samples, it is hypothesised that cells in the mesohyl store a stiffening factor and that the physiologically controlled release of this factor is responsible for the touch-induced stiffening of intact animals.

Lectin histochemistry and ultrastructure of microgranular cells in Cinachyra tarentina (Porifera, Demospongiae)

A histochemical study is described that characterizes microgranular cells of the demosponge Cinachyra tarentina (C. tarentina) with the use of routine staining methods for mucosubstances, lectin histochemistry and electron microscopy. Microgranular cells are rare or absent in other species of sponges, but abundant in this species. Microgranular cells are present in both ectosome and mesohyl, particularly along the canal of the aquiferous system and around spicule holes. Inclusions of microgranular cells and the extracellular matrix were particularly positive for acidic glycoproteins with abundant sulfated ester groups and glycosidic residues containing GalNAc and Galbeta1,3GalNAc. Terminal L-fucose bound to the penultimate GalNAc residues and/or difucosylated oligosaccharides were present as well. Our results suggest that soybean lectin (SBA), peanut lectin (PNA), and winged pea lectin (WPA) are valuable markers for identifying microgranular cells of C. tarentina. Electron microscopy revealed some of the microgranular cells to contain small smooth cytoplasmic vesicles originating from the Golgi complex and few electron-dense granules, others were characterized by numerous secretory granules and vacuoles formed by vesicle fusion and connected with the plasma membrane. Our results suggest that microgranular cells in C. tarentina contribute to the synthesis of glycoprotein components of the extracellular matrix.

Comparative investigations on the amino-acid sequences of different isolectins from the sponge Axinella polypoides (Schmidt)

The sponge Axinella polypoides contains four different D-galactose binding lectins and one, termed lectin IV, which is specific for hexuronic acids. Only the D-galactose binding lectins were investigated in this study. The complete amino-acid sequence of lectin I, the main component in the crude extract was determined. Lectin I is a homodimer and each subunit comprises 144 amino acids with a M(r) of 15,847 +/- 10, as calculated from the sequence data and determined by mass spectrometry. Each subunit contains one intrachain disulfide bridge between positions 4 and 46. Of lectin II, only the first 49 amino acids of the NH2-terminal end were analysed. This part has 29 amino acids in common with lectin I, including a cysteine residue at position 4, also suggesting an intrachain loop in a identical position as in lectin I. The molecular mass of its subunit is 16,235 +/- 10 Da. Only the first 15 NH2-terminal amino acids of lectins III and V could be sequenced. Lectin V was identical to lectin II in all positions, whereas lectin III showed only 5 residues identical to lectins I or II. Thus, lectins I, II and III are derived from three different genes, whereas lectin V may either be a proteolytic cleavage product, or result from different splicing events or may be derived also from a separate gene. Neither of the four lectins showed any similarity to known lectin sequences of animal or plant origin.

Control of the aggregation factor-aggregation receptor interaction in sponges by protein kinase C

By means of immunobiochemical and immunocytological techniques it was found that the aggregation factor (AF) from the sponge Geodia cydonium is stored in vesicles of spherulous cells. During the reaggregation process of dissociated cells, the AF which is present extracellularly was determined to be bound to the cell-surface-associated aggregation receptor (AR) only during the initial phase (0-5 h after addition of the AF to the single cell suspension). At later stages (20 h), the AF colocalized with extracellular structures, e.g., collagen and glycoconjugates. Immobilized to nitrocellulose, the AR, a molecule with Mr of 43.5 kDa, displayed its binding affinity to the AF only if it was isolated from early aggregates (5 h). The transition of the AF-susceptible to the AF-deficient state of the plasma membrane was mimicked in vitro by incubation of plasma membranes from early aggregates with purified protein kinase C. This conversion to the AF-deficient state could be prevented by the protein kinase C inhibitor staurosporine. Together with earlier findings, which revealed that the AR is phosphorylated by protein kinase C, we propose that in the sponge system this enzyme controls intercellular processes involved in morphogenesis.

Physicochemical and functional characterization of the polymerization process of the Geodia cydonium lectin

The extracellularly localized, galactose-specific lectin from the sponge Geodia cydonium binds at one class of sites, 40 mol Ca2+/mol lectin with an association constant (Ka) of 0.3 X 10(6)M-1. Stoichiometric calculations reveal that in the extracellular milieu 22 mol Ca2+ (maximum) are complexed per mol lectin. Binding of Ca2+ to the lectin increases its apparent Mr from 44000 to 56000 (electrophoretic determination) or from 36500 to 53500 (high-pressure liquid gel chromatographical determination); the s20, w increases from 4.3 S to 4.5 S if Ca2+ is added to the lectin. In the presence of Ca2+ the lectin undergoes a conformational change perhaps by expanding the carbohydrate side chains which are terminated by galactose. Subsequently the lectin molecules polymerize to large three-dimensional clumps (diameter up to 8 micron). Turbidimetric studies reveal an inhibition of the lectin polymerization by lactose. The Ka of the lectin-lectin polymerization rises from 0.9 X 10(6)M-1 to 14.0 X 10(6)M-1 after increasing the Ca2+ concentration (from 1 microM to 100 microM). Parallel with this increase in affinity, the Ka value of the lectin-aggregation factor binding drops from 41.2 X 10(6)M-1 (1 microM Ca2+) to 1.3 X 10(6)M-1 (100 microM Ca2+). In the absence of Ca2+, the Geodia lectin forms 1-10-micron two-dimensional sheets in the presence of homologous glycoconjugates. Cell binding experiments with polyacrylamide gels, containing covalently bound galactose, show that both homologous (Geodia cydonium) and heterologous cells (L5178y) bind with a higher affinity to the lectin-polymer matrix than to the lectin-monomer one. These data suggest that lectin-polymer structures, together with lectin-glycoconjugate associates, are components of the cell-substrate adhesion system(s) of sponges in vivo.