A novel rhamnose-binding lectin family from eggs of steelhead trout (Oncorhynchus mykiss) with different structures and tissue distribution

Leukolectin is expressed in lectophages, a distinct population of zebrafish embryonic macrophages

Leukolectins (LL) belong to the tectonin-family of proteins, with functions in innate immunity. Fish larvae compensating for loss of maternal chorionic protection post-hatching, provide a model-system for studying how lectins contribute to immunity. Atlantic salmon (Ssal) LL-proteins function after secretion in mucus from dermal lectocytes, as this mucus envelops embryos and larvae. The Ssalll-gene possesses multiple putative binding sites for diverse transcription-factors, suggestive of LL-functions in non-epithelial cells. Since zebrafish (zF) perivitelline fluid (PVF) contains LL-proteins, this study aims to characterize zF-leukolectins, their cellular origin, expression and gene structure. Extracts of (10 hpf) zF-embryos contained LL-proteins, and whole mount immuno-histochemistry revealed dispersed LL-positive cells including zF-lectocytes, accounting for exocrine LL-secretion by embryos. Lectocytes are lcp1-negative, but other zF-cells co-expressed LL-proteins and lcp1-transcripts, which (at this stage) identified such non-lectocytes as early macrophages (termed lectophages). In sections, LL-expression characterized large macrophage-progenitors and smaller colonizing macrophages. RT- and RACE-PCR yielded zF-LLcDNA including parts of untranslated regions. ORF encoded 255 AAs including (19 AA) signal peptide. Processing of a primary LL-transcript to (∼1.300 nt) LL-mRNA was suggested by Northern blots. Most zebrafish-egg lectins (zFELs) possess four TECPR-domains, while five TECPR-domains were predicted for zF-LL. Minor sequence variations suggested nearly identical zF-LL isoforms. Alignment of zFEL-proteins predicted a zFEL-tree with a separate leukolectin-branch. LL-amplification using zF-DNA, revealed five exons and four introns. Predicted structures of zF- and Ssal-leukolectins showed strong structural conservation (92% sequence-identity) with shorter zF-introns 2&4, but identical introns 1&3. Non-lectocytic LL-functions were investigated further by dual in situ hybridization, revealing that only some embryonic lcp1-expressing cells in early zF-embryos co-expressed LL-transcripts. Macrophages from erythro-myeloid progenitor (EMP) are known to colonize zebrafish tissues as resident macrophages (TRM), e.g. nervous system (CNS) and epiderm. Unlike Ssal-larvae relying on yolk for months, zF-larvae switch within days to nutrition from the digestive-tract, necessitating additional immuno-protection possibly from TRMs. EMP also gives rise to microglia, the TRM of CNS. The neural tube of zF-embryos exhibited numerous small, LL-positive cells, presumably stemming from lectophage-progenitors. Functions of these LL-positive embryonic microglia (lectoglia) appear more relevant for tissue remodelling than for pathogenic threats. Lectoglia sustaining CNS-neurons suggests physiological LL-roles relevant for adult health and disease. The data focus the need for resolving whether lectophages represent an unrecognized myelogenic lineage, or whether instead, LL-expression occurs in a subpopulation of the early macrophage-lineage.

Leukolectin-proteins are synthesized and secreted by lectocytes, a distinct category of fish embryonic mucus cells

Fish perivitelline fluid (PVF) is a vital extra-embryonic compartment. At hatching, PVF-contents dissolve into the hatching fluid (HF). Analysis of Atlantic salmon HF reveals nearly hundred distinct proteins, most of which were identified by advanced mass-spectometry. However, one entity with apparent molecular weight 26 kDa, necessitated identification from its tryptic peptides. Subsequent cloning and sequencing revealed novel leukolectin-proteins. From bioinformatic analysis, leukolectins (LL) belong in the tectonin protein-family, with recognized functions in innate immunity. This study aims to identify LL-expressing cells in diverse fish species, and to characterize the ll-gene in order to predict bio-functions of leukolectins. LL-proteins were detected in HF from several fish species and one invertebrate, using polyclonal LL-specific IgGs. Embryonic LL-immunoreactive cells were numerous in Atlantic salmon, rainbow trout, fewer in Atlantic cod, and rare in Oikopleura dioica, Atlantic halibut. LL-immunoreactive cells were termed lectocytes, which corresponded to peridermal mucus-cells stained by PAS, but unstained by eosin. Hence, lectocytes and hatching-gland cells were clearly distinguished. Northern blots revealed two salmon LL-transcripts at mid-embryogenesis. Such transcripts were detected in epithelial cells of the periderm, gills and oral cavity. LL-transcripts predominated in the periderm, while choriolysin-transcripts were dominant in the gills. No co-expression of choriolysins and LL-transcripts was detected. BAC-library screening yielded salmon LL's gene-structure with 4 introns, 5 exons, TATA-box, multiple upstream putative transcription-factor binding-sites and polyadenylation site. ll-gene location on chromosome ssa17 was identified in Ssal_v3.1, the 2021-version of the salmon genome. In conclusion, larvae from several fish species are outfitted with mucus enriched by LL-proteins. Mucus cells are present in embryos of all fishes, but embryonic lectocyte-numbers are far higher in species with near total larval survival. When (maternal) chorionic first-line immuno-defence is lost at hatching, leukolectin-enriched mucus may provide vital protection for larvae.

Comparative study of structures and functional motifs in lectins from the commercially important photosynthetic microorganisms

Photosynthetic microorganisms, specifically cyanobacteria and microalgae, can synthesize a vast array of biologically active molecules, such as lectins, that have great potential for various biotechnological and biomedical applications. However, since the structures of these proteins are not well established, likely due to the presence of intrinsically disordered regions, our ability to better understand their functionality is hampered. We embarked on a study of the carbohydrate recognition domain (CRD), intrinsically disordered regions (IDRs), amino acidic composition, as well as and functional motifs in lectins from cyanobacteria of the genus Arthrospira and microalgae Chlorella and Dunaliella genus using a combination of bioinformatics techniques. This search revealed the presence of five distinctive CRD types differently distributed between the genera. Most CRDs displayed a group-specific distribution, except to C. sorokiniana possessing distinctive CRD probably due to its specific lifestyle. We also found that all CRDs contain short IDRs. Bacterial lectin of Arthrospira prokarionte showed lower intrinsic disorder and proline content when compared to the lectins from the eukaryotic microalgae (Chlorella and Dunaliella). Among the important functions predicted in all lectins were several specific motifs, which directly interacts with proteins involved in the cell-cycle control and which may be used for pharmaceutical purposes. Since the aforementioned properties of each type of lectin were investigated in silico, they need experimental confirmation. The results of our study provide an overview of the distribution of CRD, IDRs, and functional motifs within lectin from the commercially important microalgae.

An l-rhamnose-binding lectin from Nile tilapia (Oreochromis niloticus) possesses agglutination activity and regulates inflammation, phagocytosis and respiratory burst of monocytes/macrophages

Rhamnose-binding lectins (RBLs), a Ca²⁺-independent lectin family, are widely present in vertebrates and invertebrates, which involve in the innate immune response. However, the functional characterization and related regulation mechanisms of RBLs remain unclear in teleost fish. In this study, an l-rhamnose-binding lectin-like (OnRBL-L) was identified and functionally characterized from Nile tilapia (Oreochromis niloticus). The open reading frame of OnRBL-L is 678 bp encoding 225 aa. The sequence of OnRBL-L has relatively conservative characteristic peptide motifs, including YGR, DPC, and KYL-motif. Expression analysis showed that OnRBL-L was abundantly distributed in intestine tissue, and widely existed in all detected tissues. Meanwhile, the expression of OnRBL-L increased significantly in vivo (liver, spleen, head kidney, intestine, gills and peripheral blood) and in vitro (monocytes/macrophages) following challenges with two important tilapia pathogenic bacteria Streptococcus agalactiae and Aeromonas hydrophila. In addition, the recombinant OnRBL-L was found to bind and agglutinate S. agalactiae and A. hydrophila. Furthermore, OnRBL-L could participate in non-specific cellular immune defense, including reducing the expression of pro-inflammatory factors (IL-6、IL-8 and TNF-α), and enhancement of the phagocytosis and respiratory burst of MO/MФ. Overall, our results provide new insights into the understanding of RBL as an important pattern recognition molecule and regulator in non-specific cell immunity in an early vertebrate.

Antibacterial functions of a novel fish-egg lectin from spotted knifejaw (Oplegnathus punctatus) during host defense immune responses

Fish-egg lectins (FELs) have been identified in several teleost species and have been proved to play important roles in innate immune system against pathogen infection. In this study a novel fish-egg lectin (OppFEL) was identified from spotted knifejaw (Oplegnathus punctatus), and the expression patterns against bacterial infection was characterized. The amino acid sequence is highly homologous to other teleost FELs, containing five repeats of the conserved TECPR domain. Expression of OppFEL was widely observed in examined tissues, with the most abundant transcripts observed in gill, showing a pattern of tissue specific expression. The OppFEL expression was significantly up-regulated following a Gram-negative bacterium (Vibrio anguillarum) challenge in vivo, suggesting participation in host antibacterial immune responses. Recombinant OppFEL protein (rOppFEL) possessed calcium dependent binding capacities and agglutination to four Gram-negative bacterium and two Gram-positive bacterium. Sugar binding assay revealed that rOppFEL specifically bound to insoluble lipopolysaccharide and peptidoglycan. In addition, rOppFEL was also proved to have hemagglutinating activity against erythrocytes from Mus musculus, O. punctatus, Sebastes schlegelii and Paralichthys olivaceus. Dual-luciferase analysis showed that overexpression of OppFEL could suppress the activity of NF-κB in a dose dependent manner. Taken together, these results suggest that OppFEL is a unique fish-egg lectin that possesses apparent immunomodulating property and is involved in host defense against pathogens invasion.

Phytogenic feed-additive effects on channel catfish rhamnose-binding lectin levels, and susceptibility to Edwardsiella ictaluri

We investigated the effects of a phytogenic feed additive on disease susceptibility to Edwardsiella ictaluri in channel catfish Ictalurus punctatus and regulation of 6 rhamnose-binding lectin (RBL) genes. Juvenile catfish (n = 250, 13.4 ± 0.1 g) were allotted to the following treatments: control (floating diet) or EO (floating diet supplemented with essential oils; Digestarom® P.E.P. MGE). The fish were fed their respective diets for 6 wk. Following subjection to different feed treatments, all fish were exposed to pathogenic E. ictaluri by bath immersion. Another group of fish were not challenged (non-challenged controls, fed control feed). Mucosal tissue samples were taken to quantify gene expression levels of RBL on Days 1 and 2 post-challenge. After challenge, survival was higher (64.4 vs. 48.0%) in fish fed EO compared to controls (p < 0.05). Relative to non-challenged controls, gill RBL1a mRNA was higher in fish fed EO (p < 0.05) on Day 1 while gill RBL3b was higher in fish fed EO (p < 0.01) on Days 1 and 2, respectively. RBL5a in the skin and proximate small intestine did not change significantly relative to non-challenged fish on Days 1 and 2 of the disease challenge. Results demonstrate that Digestarom® P.E.P. MGE improved survival of channel catfish challenged with E. ictaluri. One of the mechanisms through which essential oils may improve survival is through upregulation of RBL1a and RBL3b in the gill.

l-rhamnose-binding lectins (RBLs) in Nile tilapia, Oreochromis niloticus: Characterization and expression profiling in mucosal tissues

Rhamnose-binding lectins (RBLs) are crucial elements associated with innate immune responses to infections and have been characterized from a variety of teleost fishes. Given the importance of RBL in teleost fishes, we sought to study the diversity and expression profiles of RBLs in an important cultured fish, Nile tilapia (Oreochromis niloticus) following experimental infection with Streptococcus agalactiae, a major cause of streptococcosis in farmed tilapia. In this study, four predicted RBL genes were identified from Nile tilapia and were designated as OnRBL3a, OnRBL3b, OnRBL3c, and OnRBL3d. These OnRBLs were composed of two tandem-repeated type five carbohydrate recognition domains (CRDs), classified as type IIIc, and all clustered together phylogenetically. OnRBL-CRDs shared conserved topology of eight cysteine residues, characteristic peptide motifs of -YGR- and -DPC- (or -FGR- and -DTC-), and similar exon/intron organization. OnRBLs had the highest expression in immune-related tissues, gills, intestine or liver. However, the changes of OnRBL expression in the gills and intestine at 2 h, 4 h and 24 h post S. agalactiae challenge were modest, suggesting that tilapia may not mediate the entry or confront the infection of S. agalactiae through induction of RBL genes. The observed expression pattern may be related to the RBL type and CRD composition, S. agalactiae pathogenesis, the accessibility of ligands on the bacterial surface, and/or the species of fish. OnRBLs characterized in this study were the first RBL members identified in Nile tilapia and their characterization will expand our knowledge of RBLs in immunity.

Isolation, Amino Acid Sequences, and Plausible Functions of the Galacturonic Acid-Binding Egg Lectin of the Sea Hare Aplysia kurodai

Egg lectins occur in a variety of animals ranging from mollusks to vertebrates. A few examples of molluscan egg lectins have been reported, including that of the sea hare Aplysia kurodai; however, their biological functions in the egg remain unclarified. We report the isolation, determination of primary structure, and possible functions of A.kurodai lectin (AKL) from the egg mass of A. kurodai. We obtained AKL as an inseparable mixture of isoproteins with a relative molecular mass of approximately 32 kDa by affinity purification. The hemagglutinating activity of AKL against rabbit erythrocytes was inhibited most potently by galacturonic acid and moderately by xylose. Nucleotide sequencing of corresponding cDNA obtained by rapid amplification of cDNA ends (RACE) allowed us to deduce complete amino acid sequences. The mature polypeptides consisted of 218- or 219-amino acids with three repeated domains. The amino acid sequence had similarities to hypothetical proteins of Aplysia spp., or domain DUF3011 of uncharacterized bacterial proteins. AKL is the first member of the DUF3011 family whose function, carbohydrate recognition, was revealed. Treatment of the egg with galacturonic acid, an AKL sugar inhibitor, resulted in deformation of the veliger larvae, suggesting that AKL is involved in organogenesis in the developmental stage of A. kurodai.

A recombinant horseshoe crab plasma lectin recognizes specific pathogen-associated molecular patterns of bacteria through rhamnose

Horseshoe crab is an ancient marine arthropod that, in the absence of a vertebrate-like immune system, relies solely on innate immune responses by defense molecules found in hemolymph plasma and granular hemocytes for host defense. A plasma lectin isolated from the hemolymph of Taiwanese Tachypleus tridentatus recognizes bacteria and lipopolysaccharides (LPSs), yet its structure and mechanism of action remain unclear, largely because of limited availability of horseshoe crabs and the lack of a heterogeneous expression system. In this study, we have successfully expressed and purified a soluble and functional recombinant horseshoe crab plasma lectin (rHPL) in an Escherichia coli system. Interestingly, rHPL bound not only to bacteria and LPSs like the native HPL but also to selective medically important pathogens isolated from clinical specimens, such as Gram-negative Pseudomonas aeruginosa and Klebsiella pneumoniae and Gram-positive Streptococcus pneumoniae serotypes. The binding was demonstrated to occur through a specific molecular interaction with rhamnose in pathogen-associated molecular patterns (PAMPs) on the bacterial surface. Additionally, rHPL inhibited the growth of P. aeruginosa PAO1 in a concentration-dependent manner. The results suggest that a specific protein-glycan interaction between rHPL and rhamnosyl residue may further facilitate development of novel diagnostic and therapeutic strategies for microbial pathogens.

L-Rhamnose-binding lectins (RBLs) in channel catfish, Ictalurus punctatus: Characterization and expression profiling in mucosal tissues

Rhamnose-binding lectins (RBLs) have recently emerged as important molecules in the context of innate immunity in teleost fishes. Previously, using RNA-seq technology, we observed marked up-regulation of a RBL in channel catfish (Ictalurus punctatus) gill following a challenge with the bacterial pathogen Flavobacterium columnare. Furthermore, the magnitude of RBL up-regulation positively correlated with disease susceptibility. Moving forward from these findings, we wished to more broadly understand RBL function, diversity, and expression kinetics in channel catfish. Therefore, in the present study we characterized the RBL gene family present in select channel catfish tissues and profiled family member expression after challenge with two different Gram-negative bacterial pathogens. Here, six RBLs were identified from channel catfish and were designated IpRBL1a, IpRBL1b, IpRBL1c, IpRBL3a, IpRBL3b, and IpRBL5a. These RBLs contained carbohydrate recognition domains (CRD) ranging from one to three domains and each CRD contained the conserved motifs of -YGR- and -DPC-. Despite a level of structural conservation, the catfish RBLs showed low full-length identity with RBLs from outside the order Siluriformes. IpRBL expression after bacterial infection varied depending on both pathogen and tissue type, suggesting that IpRBLs may exert disparate functions or exhibit distinct tissue-selective roles in the host immune response to bacterial pathogens.

Domain composition of rhamnose-binding lectin from shishamo smelt eggs and its carbohydrate-binding profiles

Osmerus (Spirinchus) lanceolatus egg lectin (OLL) is a member of the rhamnose-binding lectin (RBL) family which is mainly found in aqueous beings. cDNA of OLL was cloned, and its genomic architecture was revealed. The deduced amino acid (aa) sequence indicated that OLL was composed of 213 aa including 95 aa of domain N and 97 aa of domain C. N and C showed 73 % sequence identity and contained both -ANYGR- and -DPC-KYL-peptide motifs which are conserved in most of the RBL carbohydrate recognition domains. The calculated molecular mass of mature OLL was 20,852, consistent with the result, and 20,677.716, from mass spectrometry. OLL was encoded by eight exons: exons 1 and 2 for a signal peptide; exons 3-5 and 6-8 for N- and C-domains, respectively. Surface plasmon resonance spectrometric analyses revealed that OLL showed comparable affinity for Galα- and β-linkages, whereas Silurus asotus lectin (SAL), a catfish RBL, bound preferentially to α-linkages of neoglycoproteins. The Kd values of OLL and SAL against globotriaosylceramide (Gb3) were 1.69 × 10⁻⁵ M for and 2.81 × 10⁻⁶ M, respectively. Thus, the carbohydrate recognition property of OLL is slightly different from that of SAL. On the other hand, frontal affinity chromatography revealed that both OLL and SAL interacted with only glycolipid-type oligosaccharides such as Gb3 trisaccharides, not with N-linked oligosaccharides. The domain composition of these RBLs and an analytical environment such as the "cluster effect" of a ligand might influence the binding between RBL and sugar chains.

Transcriptomic signatures of attachment, NF-κB suppression and IFN stimulation in the catfish gill following columnaris bacterial infection

Outbreaks of columnaris disease (Flavobacterium columnare) are common in wild and cultured freshwater fish worldwide. Disease occurrences, particularly those caused by virulent genomovar II isolates, in aquaculture species such as channel catfish can be devastating. In contrast to other important aquaculture pathogens, little is known about host immune responses to columnaris. Adhesion of F. columnare to gill tissue has been correlated in some previous studies to virulence and host susceptibility. Here, therefore, we conducted the first transcriptomic profiling of host responses to columnaris following an experimental challenge. We utilized Illumina-based RNA-seq expression profiling to examine transcript profiles at three timepoints (4h, 24h, and 48h) in catfish gill after bath immersion infection. Enrichment and pathway analyses of the differentially expressed genes revealed several central signatures following infection. These included the dramatic upregulation of a rhamnose-binding lectin, with putative roles in bacterial attachment and aggregation, suppression of NF-κB signalling via IκBs, BCL-3, TAX1BP1, and olfactomedin 4, and strong induction of IFN-inducible responses including iNOS2b, IFI44, and VHSV genes. Fifteen differentially expressed genes with varying expression profiles by RNA-seq, were validated by QPCR (correlation coefficients 0.85-0.94, p-value <0.001). Our results highlight several putative immune pathways and individual candidate genes deserving of further investigation in the context of development of therapeutic regimens and laying the foundation for selection of resistant catfish lines against columnaris.

Molecular characterisation and expression analysis of a fish-egg lectin in rock bream, and its response to bacterial or viral infection

A fish-egg lectin, RbFEL, was identified from rock bream (Oplegnathus fasciatus) and its expression analysed. In both vertebrates and invertebrates, carbohydrate-binding proteins (lectins) play an important role in innate immunity against microbial invasion. Here, we report the cloning of a fish-egg lectin from rock bream using a combination of expression sequence tag (EST) analyses. The full-length cDNA of RbFEL is composed of 1512-bp with a 780-bp ORF that encodes 259 amino acid residues. The deduced polypeptide exhibits six conserved residues of the FEL family. All cysteine positions in each domain were completely conserved. Reverse transcription quantitative real-time PCR analysis of the tissues revealed that RbFEL mRNA was abundantly expressed in liver, moderately expressed in head kidney and rarely expressed in other tissues. Expression analyses of time series sampled fertilised eggs showed that expression gradually increased 1, 3, 12, 24 and 36 h after fertilisation. In addition, RbFEL expression was significantly up-regulated in rock bream challenged with Edwardsiella tarda, Streptococcus iniae and red sea bream iridovirus (RSIV). These results suggest that RbFEL is a member of the egg-lectin family and is involved in the innate immune response in rock bream.

Diversified carbohydrate-binding lectins from marine resources

Marine bioresources produce a great variety of specific and potent bioactive molecules including natural organic compounds such as fatty acids, polysaccharides, polyether, peptides, proteins, and enzymes. Lectins are also one of the promising candidates for useful therapeutic agents because they can recognize the specific carbohydrate structures such as proteoglycans, glycoproteins, and glycolipids, resulting in the regulation of various cells via glycoconjugates and their physiological and pathological phenomenon through the host-pathogen interactions and cell-cell communications. Here, we review the multiple lectins from marine resources including fishes and sea invertebrate in terms of their structure-activity relationships and molecular evolution. Especially, we focus on the unique structural properties and molecular evolution of C-type lectins, galectin, F-type lectin, and rhamnose-binding lectin families.

Molecular cloning of rhamnose-binding lectin gene and its promoter region from snakehead Channa argus

Lectins are sugar-binding proteins that mediate pathogen recognition and cell-cell interactions. A rhamnose-binding lectin (RBL) gene and its promoter region have been cloned and characterized from snakehead Channa argus. From the transcription initiation site, snakehead rhamnose-binding lectin (SHL) gene extends 2,382 bp to the end of the 3' untranslated region (UTR), and contains nine exons and eight introns. The open reading frame (ORF) of the SHL transcript has 675 bp which encodes 224 amino acids. The molecular structure of SHL is composed of two tandem repeat carbohydrate recognition domains (CRD) with 35% internal identity. Analysis of the gene organization of SHL indicates that the ancestral gene of RBL may diverge and evolve by exon shuffling and gene duplication, producing new forms to play their own roles in various organisms. The characteristics of SHL gene 5' flanking region are the presence of consensus nuclear factor of interleukin 6 (NF-IL6) and IFN-gamma activation (GAS) sites. The results provide indirect evidence that up-regulation of SHL expression may be induced in response to inflammatory stimuli, such as lipopolysaccharide (LPS), interleukin 6 (IL-6), and interferon gamma (IFN-gamma). The transcript of SHL mRNA was expressed in the head kidney, posterior kidney, spleen, liver, intestine, heart, muscle, and ovary. No tissue-specific expressive pattern is different from reported STLs, WCLs, and PFLs, suggesting that different types of RBLs exist in species-specific fish that have evolved and adapted to their surroundings.

Comparative analysis of the testis and ovary transcriptomes in zebrafish by combining experimental and computational tools

Studies on the zebrafish model have contributed to our understanding of several important developmental processes, especially those that can be easily studied in the embryo. However, our knowledge on late events such as gonad differentiation in the zebrafish is still limited. Here we provide an analysis on the gene sets expressed in the adult zebrafish testis and ovary in an attempt to identify genes with potential role in (zebra)fish gonad development and function. We produced 10,533 expressed sequence tags (ESTs) from zebrafish testis or ovary and downloaded an additional 23,642 gonad-derived sequences from the zebrafish EST database. We clustered these sequences together with over 13,000 kidney-derived zebrafish ESTs to study partial transcriptomes for these three organs. We searched for genes with gonad-specific expression by screening macroarrays containing at least 2600 unique cDNA inserts with testis-, ovary- and kidney-derived cDNA probes. Clones hybridizing to only one of the two gonad probes were selected, and subsequently screened with computational tools to identify 72 genes with potentially testis-specific and 97 genes with potentially ovary-specific expression, respectively. PCR-amplification confirmed gonad-specificity for 21 of the 45 clones tested (all without known function). Our study, which involves over 47,000 EST sequences and specialized cDNA arrays, is the first analysis of adult organ transcriptomes of zebrafish at such a scale. The study of genes expressed in adult zebrafish testis and ovary will provide useful information on regulation of gene expression in teleost gonads and might also contribute to our understanding of the development and differentiation of reproductive organs in vertebrates.

SUEL-related lectins, a lectin family widely distributed throughout organisms

Glycan-binding proteins are categorized into two groups, lectins and sulfated glycosaminoglycan-binding proteins. SUEL-related lectins are members of a superfamily of proteins containing a carbohydrate-recognition domain (CRD), which is structurally similar to sea urchin egg lectin (SUEL). Here I review the structure and function of this family of proteins.

Evaluation of silica gel-immobilized phosphorylcholine columns for size exclusion chromatography and their application in the analysis of the subunit structures of fish-egg lectins

Columns of phosphorylcholine (PC) immobilized on silica gel were shown to be useful for size exclusion chromatography (SEC) of proteins. The columns provided good separation of proteins in 50mM sodium phosphate buffer (pH 6.9) containing 0.25 M NaCl, and there was a linear relationship between the retention times and the logarithmic values of the molecular weights with a correlation coefficient (R(2)) of 0.978-0.992. The columns were used in analyzing the subunit structures of the rhamnose-binding lectins CSL1, CSL2, and CSL3, isolated from chum salmon (Oncorhynchus keta) eggs. Although the lectins, which are a group of carbohydrate-binding and hydrophobic proteins, behaved anomalously in SEC with conventional matrices, they could be eluted from the immobilized PC columns without non-size-related retention, thereby allowing their molecular weights to be reliably estimated.

Gas-phase scrambling of disulfide bonds during matrix-assisted laser desorption/ionization mass spectrometry analysis

Evidence for photo-induced radical disulfide bond scrambling in the gas phase during matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is described. The phenomenon was observed during the analysis of tryptic peptides from insulin and was confirmed in the determination of disulfide bonds in the rhamnose-binding lectin SEL24K from the Chinook salmon Oncorhynchus tshawytscha. A possible mechanism for this surprising scrambling is proposed. Despite this finding, the disulfide bond pattern in SEL24K was assigned unambiguously by a multi-enzyme digestion strategy in combination with MALDI mass spectrometry. The pattern was found to be symmetrical in the tandem repeat sequence of SEL24K. To the best of our knowledge, this is the first report of disulfide bond scrambling in the gas phase during MALDI-MS analysis. This observation has important ramifications for unambiguous assignment of disulfide bonds.

Stimulation of growth and changes in the hepatic transcriptome by 17β-estradiol in the yellow perch (Perca flavescens)

The effects of dietary 17β-estradiol (E2) on growth and liver transcriptomics were investigated in the yellow perch ( Perca flavescens). After a 3-mo treatment, E2 significantly stimulated an increase in length and weight of juvenile male and female perch relative to control animals. The increase was significantly greater in females compared with males. Separate, unnormalized cDNA libraries were constructed from equal quantities of RNA from 6 male and 6 female livers of E2-treated and control perch, and 3,546 and 3,719 expressed sequence tags (ESTs) were obtained, respectively. To characterize E2-regulated transcripts, EST frequencies between libraries were calculated within contiguous sequences that were assembled from the combined ESTs of both libraries. Frequencies were also determined in EST transcript groupings produced by aligning all of the ESTs from both libraries at the nucleotide level. From these analyses, there were 28 annotated transcripts that were regulated by 75% between libraries and for which there were at least 5 ESTs of the same transcript between libraries. Regulation of a subset ( 14 ) of these transcripts was confirmed by quantitative reverse transcription-polymerase chain reaction (QPCR). Transcripts that were upregulated by E2 included reproduction-related proteins, binding proteins, and proteases and protease inhibitors. While not part of the transcript frequency analysis, QPCR showed significant upregulation of estrogen receptor esr1 and of insulin-like growth factor I (IGF-I) in E2 livers. E2-downregulated transcripts represented a variety of functional categories including components of the respiratory chain, lipid transport and metabolism, glycolysis, amino acid and nitrogen metabolism, binding proteins, a hydrolytic enzyme, and a transcriptional regulator. In perch it appears that exogenous estrogen drastically shifts liver metabolism toward the production of lipoproteins and carbohydrate binding proteins, and that the growth-promoting action may involve an increase in hepatic IGF-I production.

Structure of rhamnose-binding lectin CSL3: unique pseudo-tetrameric architecture of a pattern recognition protein

The crystal structure of the L-rhamnose-binding lectin CSL3 was determined to 1.8 A resolution. This protein is a component of the germline-encoded pattern recognition proteins in innate immunity. CSL3 is a homodimer of two 20 kDa subunits with a dumbbell-like shape overall, in which the N- and C-terminal domains of different subunits form lobe structures connected with flexible linker peptides. The complex structures of the protein with specific carbohydrates demonstrated the importance of the most variable loop region among homologues for the specificity toward oligosaccharides. CSL3 and Shiga-like toxin both use Gb(3) as a cellular receptor to evoke apoptosis. They have very different overall architecture but share the separation distance between carbohydrate-binding sites. An inspection of the structure database suggested that the pseudo-tetrameric structure of CSL3 was unique among the known lectins. This architecture implies this protein might provide a unique tool for further investigations into the relationships between architecture and function of pattern recognition proteins.

The function of rhamnose-binding lectin in innate immunity by restricted binding to Gb3

L-rhamnose-binding lectins (RBLs) have been isolated from various kinds of fish and invertebrates and interact with various kinds of bacteria, suggesting RBLs are involved in various inflammatory reactions. We investigated the effect of RBLs from chum salmon (Oncorhynchus keta), named CSL1, 2 and 3, on the peritoneal macrophage cell line from rainbow trout (Oncorhynchus mykiss) (RTM5) and an established fibroblastic-like cell line derived from gonadal tissue of rainbow trout (RTG-2). CSLs were bound to the surface of RTM5 and RTG-2 cells and induced proinflammatory cytokines, including IL-1beta1, IL-1beta2, TNF-alpha1, TNF-alpha2 and IL-8 in both cells by recognizing globotriaosylceramide (Gb3). In addition, CSLs had an opsonic effect on RTM5 cells and this effect was significantly inhibited by L-rhamnose, indicating that CSLs enhanced their phagocytosis by binding to Gb3 on cell surfaces. This is the first finding that Gb3 plays a role in innate immunity by cooperating with natural ligands, RBLs.

Novel rhamnose-binding lectins from the colonial ascidian Botryllus schlosseri

In a full-length cDNA library from the compound ascidian Botryllus schlosseri, we identified, by BLAST search against UniProt database, five transcripts, each with complete coding sequence, homologous to known rhamnose-binding lectins (RBLs). Comparisons of the predicted amino acid sequences suggest that they represent different isoforms of a novel RBL, called BsRBL-1-5. Four of these isolectins were found in Botryllus homogenate after purification by affinity chromatography on acid-treated Sepharose, analysis by reverse-phase HPLC and mass spectrometry. Analysis of both molecular masses and tryptic digests of BsRBLs indicated that the N-terminal sequence of the purified proteins starts from residue 22 of the putative amino acid sequence, and residues 1-21 represent a signal peptide. Analysis by mass spectrometry of V8-protease digests confirmed the presence and alignments of the eight cysteines involved in the disulphide bridges that characterise RBLs. Functional studies proved the enhancing effect on phagocytosis of the affinity-purified material. Results are discussed in terms of phylogenetic relationships of BsRBLs with orthologous molecules from protostomes and deuterostomes.

Isolation and characterization of l-rhamnose-binding lectin, which binds to microsporidian Glugea plecoglossi, from ayu (Plecoglossus altivelis) eggs

A rhamnose-binding lectin, named SFL, was isolated from the eggs of ayu (sweet fish, Plecoglossus altivelis) by affinity and ion-exchange chromatographies. SFL revealed 287 amino acid residues with 3 tandemly repeated domains, and contained 8 half-Cys residues in each domain. The lectin was shown to have a highly specific binding affinity to globotriaosylceramide (Gb3) by frontal affinity chromatography using 100 oligosaccharides. SFL was localized in several tissues and serum of both male and female ayu, such as gill, liver, ovary, testis, intestine, stomach, brain, kidney and serum. The lectin agglutinated the spores of the microsporidian Glugea plecoglossi, which is a pathogen of ayu. Although SFL bound to glycoproteins and glycolipids of G. plecoglossi spores, Gb3 could not be detected in either of them. The results suggest that SFL could interact with various glycoconjugates of pathogens to play a role in the adhesion of microorganisms invading in the body.

The disulfide bond pattern of salmon egg lectin 24K from the Chinook salmon Oncorhynchus tshawytscha

The disulfide bonds in the galactose-specific lectin SEL 24K from the egg of the Chinook salmon Oncorhynchus tshawytscha were determined by mass spectrometry. Four predictive in silico tools were used to determine the oxidation state of cysteines in the sequence and possible location of the disulfide bonds. A combination of tryptic digestion, HPLC separation, and chemical modifications were used to establish the location of seven disulfide bonds and one pair of free cysteines. After proteolysis, peptides containing one or two disulfide bonds were identified by reduction and mass spectral comparison. MALDI mass spectrometry was supported by chemical modification (iodoacetamide) and in silico digestion. The assignments of disulfide bonds were further confirmed by mass spectral fragmentation studies including in-source dissociation (ISD) and collision-induced dissociation (CID). The experimentally determined disulfide bonds and free Cys residues were only partially consistent with those generated by several automated public-domain algorithms.

Purification, cloning and characterization of egg lectins from the teleost Tribolodon brandti

Three L-rhamnose-binding egg lectins, TBL1, TBL2 and TBL3, were isolated from the eggs of the Far East dace Tribolodon brandti by a combination of affinity chromatography on L-rhamnose-Sepharose 6B gel and reversed-phase HPLC. L-rhamnose is a common inhibitor of the purified lectins and strongly inhibited the hemagglutinating activity of TBL2 and TBL3, but less weakly that of TBL1. L-arabinose, which has the same hydroxyl group orientation at C2 and C4 as L-rhamnose, and D-galactose showed no inhibitory activity against TBL1 but showed weak inhibitory activity against TBL2 and TBL3. The open reading frames of the cDNAs of TBL1, TBL2 and TBL3 encoded for mature proteins of 207, 189, and 293 amino acid residues, respectively. A BLAST homology search showed that the TBLs have about 40% homology to the carbohydrate recognition domains of rhamnose-binding lectins in salmonid eggs. The tandem repeated domains present in TBL1, TBL2 and TBL3 were two, two and three, respectively. TBL2 was exclusively expressed in ovary, while TBL1 and TBL3 were expressed mainly in ovary and weakly in various tissues including gill, heart, kidney, liver, spleen and testis.

A gene family of putative immune recognition molecules in the hydroid Hydractinia

Animal taxa display a wide array of immune-type receptors that differ in their specificities, diversity, and mode of evolution. These molecules ensure effective recognition of potential pathogens for subsequent neutralization and clearance. We have characterized a family of putative immune recognition molecules in the colonial hydroid Hydractinia symbiolongicarpus. A complementary DNA fragment with high similarity to the sea urchin L: -rhamnose-binding lectin was isolated and used to screen 9.5 genome equivalents of a H. symbiolongicarpus bacterial artificial chromosome library. One of the resulting 19 positive clones was sequenced and revealed the presence of a 5,111-bp gene organized in 13 exons and 12 introns. The gene was predicted to encode a 726-amino acid secreted modular protein composed of a signal peptide, an anonymous serine-rich domain, eight thrombospondin type 1 repeats, and a L: -rhamnose-binding lectin domain. The molecule was thus termed Rhamnospondin (Rsp). Southern hybridization and sequence analyses indicated the presence of a second Rsp gene. The cDNA from both Rsp genes was sequenced in 18 individuals, revealing high levels of genetic polymorphism. Nucleotide substitutions were distributed throughout the molecule and showed a significantly higher number of synonymous substitutions per synonymous sites than its nonsynonymous counterparts. Whole-mount in situ hybridization and semi-quantitative reverse transcription polymerase chain reaction of microorganism-challenged colonies indicated that Rsp molecules were specifically and constitutively expressed in the hypostome of gastrozooids' mouth. Thus, the combination of (1) comparative analysis on domain composition and function, (2) polymorphism, and (3) expression patterns, suggest that Rsp genes encode a family of putative immune recognition receptors, which may act by binding microorganisms invading the colony through the polyp's mouth.

Isolation, characterization and molecular evolution of a novel pearl shell lectin from a marine bivalve, Pteria penguin

A novel lectin, PPL, was isolated from the mantle of penguin wing oyster (Pteria penguin) by affinity chromatography on mucin-Sepharose 4B and cation exchange chromatography on HiTrap SP. This lectin was estimated to be a 21-kDa monomer by gel filtration, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted time of flight (MALDI-TOF) mass spectrometry. However, dynamic light scattering experiments revealed that a non-covalently linked dimer formed under high salt conditions (500 mM NaCl). Interestingly, PPL showed an increasing hemagglutinating activity with increasing salt concentration. The amino acid sequence of PPL was determined by direct protein sequence analysis and cDNA cloning. The 167-amino acid sequence included 24 lysine residues and had two tandemly repeated homologous domains (residues 20-78 and 107-165) with 44% internal homology. PPL showed sequence homology to L-rhamnose-binding lectins from fish eggs and a D-galactose-binding lectin from sea urchin eggs, with sequence identities in the range 37-48%. PPL agglutinated various animal erythrocytes independently of calcium ions. The minimum concentration of PPL needed to agglutinate rabbit erythrocytes was 0.5 micro g/ml, and the most effective saccharides to inhibit the hemagglutination were D-galactose, methyl-D-galactopyranoside and N-acetyl-D-lactosamine. Lactose also inhibited hemagglutination, but L-rhamnose did so only weakly despite the sequence homology with trout egg L-rhamnose-binding lectins. The carbohydrate-binding specificity of PPL was further examined by frontal affinity chromatography using 37 different pyridylaminated oligosaccharides. PPL was found to have strong binding affinity for various oligosaccharides that have Galbeta1-4Glu/GlcNAc, Galbeta1-3GalNAc/GlcNAc and Galalpha 1-4Gal moieties in their structure. PPL had a high thermal stability and retained 50% of its hemagglutinating activity after incubation at 70 degrees C for 100 min. It agglutinated some Gram-negative bacteria by recognizing lipopolysaccharides. Together, these results suggest that PPL is a new member of the trout egg lectin family which participates in the self-defense mechanism against bacteria and pathogens with a distinct carbohydrate-binding specificity. We conclude that the trout egg lectin family proteins, in particular their carbohydrate recognition domains, have acquired diverse carbohydrate-binding specificities during molecular evolution.

Structural characterization of a rhamnose-binding glycoprotein (lectin) from Spanish mackerel (Scomberomorous niphonius) eggs

A rhamnose-binding glycoprotein (lectin), named SML, was isolated from the eggs of Spanish mackerel (Scomberomorous niphonius) by affinity and ion-exchange chromatographies. SML was composed of a non-covalently linked homodimer. The SML subunit was composed of 201 amino acid residues with two tandemly repeated domains, and contained 8 half-Cys residues in each domain, which is highly homologous to the N-terminal lectin domain of calcium-independent alpha-latrotoxin receptor in mammalian brains. Each domain has the same disulfide bonding pattern; Cys10-Cys40, Cys20-Cys99, Cys54-Cys86 and Cys67-Cys73 were located in the N-terminal domain, and Cys108-Cys138, Cys117-Cys195, Cys152-Cys182 and Cys163-Cys169 were in the C-terminal domain. SML was N-glycosylated at Asn168 in the C-terminal domain. The structure of the sugar chain was determined to be NeuAc-Galbeta1-4GlcNAcbeta1-2Manalpha1-6-(NeuAc-Galbeta1-4GlcNAcbeta1-2Manalpha1-3)Manbeta1-4GlcNAcbeta1-4GlcNAc-Asn.

Carbohydrate-binding site of a novel mannose-specific lectin from fugu (Takifugu rubripes) skin mucus

Pufflectin-s, identified in the skin mucus of the fugu Takifugu rubripes, is a novel mannose-specific lectin with similar structure to monocotyledonous plant lectins. In the present study, mutational analysis was used to reveal the mannose-binding sites of pufflectin-s. Putative binding sites were mutated as follows: binding site 1; rPL-D32E (Asp32-->Glu32), rPL-N34S (Asn34-->Ser34) and rPL-V36A (Val36-->Ala36) whereas binding site 2; rPL-D61E (Asp61-->Glu61), rPL-N63S (Asn63-->Ser63) and rPL-V65A (Val65-->Ala65). All recombinant proteins were expressed in Escherichia coli, purified with two chromatographic steps, and then subjected to mannose-binding assay by affinity chromatography. Recombinant wild-type pufflectin-s (rPL-wt) as well as three mutants with changes in binding site 2 could bind to mannose, in contrast to the three mutants with changes in binding site 1 in which mannose-binding activity was completely lost. These results clearly demonstrate that, at the least, binding site 1 is critical to mannose-binding activity in pufflectin-s.

Molecular phenotype of zebrafish ovarian follicle by serial analysis of gene expression and proteomic profiling, and comparison with the transcriptomes of other animals

BACKGROUND

The ability of an oocyte to develop into a viable embryo depends on the accumulation of specific maternal information and molecules, such as RNAs and proteins. A serial analysis of gene expression (SAGE) was carried out in parallel with proteomic analysis on fully-grown ovarian follicles from zebrafish (Danio rerio). The data obtained were compared with ovary/follicle/egg molecular phenotypes of other animals, published or available in public sequence databases.

RESULTS

Sequencing of 27,486 SAGE tags identified 11,399 different ones, including 3,329 tags with an occurrence superior to one. Fifty-eight genes were expressed at over 0.15% of the total population and represented 17.34% of the mRNA population identified. The three most expressed transcripts were a rhamnose-binding lectin, beta-actin 2, and a transcribed locus similar to the H2B histone family. Comparison with the large-scale expressed sequence tags sequencing approach revealed highly expressed transcripts that were not previously known to be expressed at high levels in fish ovaries, like the short-sized polarized metallothionein 2 transcript. A higher sensitivity for the detection of transcripts with a characterized maternal genetic contribution was also demonstrated compared to large-scale sequencing of cDNA libraries. Ferritin heavy polypeptide 1, heat shock protein 90-beta, lactate dehydrogenase B4, beta-actin isoforms, tubulin beta 2, ATP synthase subunit 9, together with 40 S ribosomal protein S27a, were common highly-expressed transcripts of vertebrate ovary/unfertilized egg. Comparison of transcriptome and proteome data revealed that transcript levels provide little predictive value with respect to the extent of protein abundance. All the proteins identified by proteomic analysis of fully-grown zebrafish follicles had at least one transcript counterpart, with two exceptions: eosinophil chemotactic cytokine and nothepsin.

CONCLUSION

This study provides a complete sequence data set of maternal mRNA stored in zebrafish germ cells at the end of oogenesis. This catalogue contains highly-expressed transcripts that are part of a vertebrate ovarian expressed gene signature. Comparison of transcriptome and proteome data identified downregulated transcripts or proteins potentially incorporated in the oocyte by endocytosis. The molecular phenotype described provides groundwork for future experimental approaches aimed at identifying functionally important stored maternal transcripts and proteins involved in oogenesis and early stages of embryo development.

Tandem repeat L-rhamnose-binding lectin from the skin mucus of ponyfish, Leiognathus nuchalis

Two lactose-binding lectins (PFL-1 and -2) were identified in the skin mucus of ponyfish, Leiognathus nuchalis. The molecular masses of PFL-1 and -2 were estimated to be 24 and 30kDa, respectively. Cloning of the PFL-1 cDNA demonstrated its unique tandem repeat structure composed of two homologous domains with 41.7% internal identity. Furthermore, PFL-1 exhibited homology with L-rhamnose-binding lectins previously purified from the eggs of fish and sea urchins. The N-terminal amino acid sequence of PFL-2 was similar to that of PFL-1, suggesting that this protein is an isotype of PFL-1. The PFL-1 gene was expressed in the skin, an important line of defense against pathogens in fish, but was not expressed in any of the other tissues tested here. PFL-1 is the fourth type of fish skin mucus lectin to be identified, suggesting that different species of fish express different types of lectin in their skin mucus.

Transcriptome analysis of zebrafish embryogenesis using microarrays

Zebrafish (Danio rerio) is a well-recognized model for the study of vertebrate developmental genetics, yet at the same time little is known about the transcriptional events that underlie zebrafish embryogenesis. Here we have employed microarray analysis to study the temporal activity of developmentally regulated genes during zebrafish embryogenesis. Transcriptome analysis at 12 different embryonic time points covering five different developmental stages (maternal, blastula, gastrula, segmentation, and pharyngula) revealed a highly dynamic transcriptional profile. Hierarchical clustering, stage-specific clustering, and algorithms to detect onset and peak of gene expression revealed clearly demarcated transcript clusters with maximum gene activity at distinct developmental stages as well as co-regulated expression of gene groups involved in dedicated functions such as organogenesis. Our study also revealed a previously unidentified cohort of genes that are transcribed prior to the mid-blastula transition, a time point earlier than when the zygotic genome was traditionally thought to become active. Here we provide, for the first time to our knowledge, a comprehensive list of developmentally regulated zebrafish genes and their expression profiles during embryogenesis, including novel information on the temporal expression of several thousand previously uncharacterized genes. The expression data generated from this study are accessible to all interested scientists from our institute resource database (http://giscompute.gis.a-star.edu.sg/~govind/zebrafish/data_download.html).

Isolation of the salmonid rhamnose-binding lectin STL2 from spores of the microsporidian fish parasite Loma salmonae

The microsporidian parasite, Loma salmonae, is the causative agent of gill disease in both wild and netpen-reared salmonids worldwide. In this paper we report the finding of a rhamnose-binding lectin from steelhead trout, Oncorhynchus mykiss, which was found bound in high concentration to the surface coat of L. salmonae spores. SDS-PAGE, immunoblot, N-terminal sequencing and mass spectrometric analyses were used to determine that the dominant 24 kDa protein lectin observed on SDS-PAGE analysis of intact spore extracts is the O. tshawytscha variant of the previously identified rhamnose-binding lectin STL2 from rainbow trout, O. mykiss. Although the physiological role of these lectins has not been clearly delineated, they have been implicated in a variety of functions, including inhibition of pathogenic bacteria by opsonization and macrophage-mediated tumour lysis.

Isolation and characterization of a glucose/mannose/rhamnose-specific lectin from the knife bean Canavalia gladiata

A lectin with specificity toward mannose, glucose, and rhamnose has been isolated from the legumes of the knife bean Canavalia gladiata. The lectin is composed of two identical 30-kDa subunits with substantial N-terminal sequence similarity to Concanavalin A (Con A). It was purified by affinity chromatography on Affi-gel blue gel, ion exchange chromatography on Mono S, and gel filtration by fast protein liquid chromatography on Superdex 200. Compared with Con A, knife bean lectin started to stimulate [methyl-(3)H]thymidine uptake by mouse splenocytes at a lower concentration, and more potently inhibited proliferation of L1210 leukemia cells. In contrast to Con A, the mitogenic activity of knife bean lectin toward mouse splenocytes, but not its antiproliferative activity toward tumor cells, could be abrogated by 250 mM glucose. Both mitogenic and antiproliferative activities of Con A were abolished by glucose. The lectin inhibited HIV-1 reverse transcriptase with an IC(50) of 35 microM and cell-free translation in a rabbit reticulocyte lysate system with an IC(50) of 2.08 microM. The lectin did not exhibit antifungal activity.

Genome-wide identification of female-enriched genes in zebrafish

Characteristic differences in morphology, physiology, and behavior between a male and female are correlated to the differential selection of sex-dependent transcriptomes. By using a cDNA array carrying approximately 9,000 zebrafish unique genes, we identified a group of genes whose expression are enriched in the female fish. A subset of these genes have been confirmed and further grouped as egg-enriched genes, as both somatic- and egg-enriched genes or as somatic-enriched genes by means of RNA gel blot hybridization. Most importantly, a significant proportion of these genes are either functionally unknown or are novel genes. Thus, future studies of this group of genes will help us greatly to understand more about sex-determination and sex-related physiology and behavior. In addition, comparison of zebrafish female-enriched genes with that in Drosophila, we found that only germline genes are shared between vertebrate and invertebrate, suggesting that the process of oogenesis is highly conserved during the evolution.

The immunostimulatory activity and stability of grass carp (Ctenopharyngodon idellus) roe lectin

A hexameric rhamnose-specific lectin with a molecular mass of 205kDa and exhibiting some N-terminal sequence similarity to other fish lectins was isolated from roe of the grass carp (Ctenopharyngodon idellus) by affinity chromatography on rhamnose-Sepharose and ion exchange chromatography by fast protein liquid chromatography on a Mono S column. The lectin exhibited mitogenic activity toward murine splenocytes with a potency lower than that of the plant lectin ConA. It exerted a stimulatory effect at a concentration of 10 micro g/ml on the phagocytic activity of seabream (Sparus sarba) macrophages. It was unstable toward heat (temperature > or =40 degrees C), acid (0.1M HCl), alkali (0.1M NaOH), trypsin and succinylation.

Purification and characterization of a rhamnose-binding lectin with immunoenhancing activity from grass carp (Ctenopharyngodon idellus) ovaries

A rhamnose-specific lectin was isolated from ovaries of the grass carp (Ctenopharyngodon idellus). The grass carp lectin possesses a molecular mass of 205 kDa. It is composed of six subunits each with a molecular mass of 35 kDa. The N-terminal amino acid sequence of the grass carp shows similarity to those of other fish species with 26-35% amino acid identity. It is mitogenic toward murine splenocytes and peritoneal exudate cells.

Expressed sequence tag analysis of expression profiles of zebrafish testis and ovary

In the present study, two gonad cDNA libraries from zebrafish testes and ovaries were constructed and a total of 1025 expressed sequence tag (EST) clones were generated from the two libraries: 501 from the testis library and 524 from the ovary library. A total of 641 of the EST clones were identified to share significant sequence identity with known sequences in GenBank, representing at least 478 different zebrafish genes. In order to understand the molecular compositions of the two gonad organs, the expression profiles of the identified clones in these two gonad cDNA libraries were analyzed. Both gonad libraries have a higher portion of clones for nuclear proteins and a lower portion for proteins in translational machinery, cytoskeleton and mitochondria than our previously characterized whole-adult cDNA library. Most abundant cDNA clones in the two gonad libraries were identified and over 10% of ovary clones were found to encode egg membrane proteins (zona pellucida or ZP proteins). Furthermore, the testis library showed a more even distribution of cDNA clones with relatively fewer abundant clones that tend to contribute redundant clones in EST projects; thus, the testis library can supply more unique and novel cDNA sequences in a zebrafish EST project. Another aim of this study is to identify cDNA clones that can be used as molecular markers for the analysis of the gonad development in zebrafish. Eleven potential clones were selected to analyze their expression patterns by Northern blot hybridization. Most of them showed a specific or predominant expression in the expected testis or ovary tissue. At last, four of the clones were found, by section in situ hybridization, to be expressed specifically in the germ cells of the testis or ovary and thus they are suitable molecular markers for analyses of spermatogenesis and oogenesis.

Immunohistochemical localization of rhamnose-binding lectins in the steelhead trout (Oncorhynchus mykiss)

The localization of three -rhamnose-binding lectins named STL1, STL2, and STL3 from eggs of steelhead trout (Oncorhynchus mykiss) was analyzed by indirect immunohistochemical staining with specific antisera against individual lectins. In early previtellogenic oocyte, STL1 was localized not only in the cortical vesicles, but also in the plasma membrane and germinal vesicle. On the other hand, STL2 and STL3 were localized only in the cortical vesicles. In pre-fertilization mature egg, STLs were localized in a thin layer of cortical granules at the cytoplasmic side of the plasma membrane. STLs were accumulated on the surface of cytoplasm and inner membrane 30 min after fertilization. The strong staining with anti-STL1 antiserum was observed in several tissues and cells of the steelhead trout, such as spleen, thrombocytes, and blood leukocytes, but not erythrocytes. STL1 was also identified in exocrine cells, such as goblet cells of intestine and mucous cells of gill. These results indicate that the multiple lectins found in eggs of the steelhead trout play physiological roles not only in eggs, but also in various cells related to the innate immunity.

Tissue-specific expression of rhamnose-binding lectins in the steelhead trout (Oncorhynchus mykiss)

Tissue-specific expression of three L-rhamnose-binding lectins, named STL1, STL2, and STL3, in the steelhead trout (Oncorhynchus mykiss) was investigated. STL2 and STL3 mRNAs were restricted in the oocytes. In contrast, STL1 mRNA was detected only in the liver. The transcription of STL2 and STL3 started in previtellogenic oocytes. These results showed distinct expression profiles of rhamnose-binding lectins in the fish.

Distribution and molecular evolution of rhamnose-binding lectins in Salmonidae: isolation and characterization of two lectins from white-spotted Charr (Salvelinus leucomaenis) eggs

L-Rhamnose-binding lectins were isolated from white-spotted charr (Salvelinus leucomaenis) eggs to understand the distribution and molecular evolution of the lectins in Salmonidae. Only two L-rhamnose-binding lectins, named WCL1 and WCL3, were isolated from white-spotted charr eggs, though three lectins, named STL1, STL2, and STL3, had been obtained from steelhead trout (Oncorhynchus mykiss) eggs. The cDNAs of WCL1 and WCL3 included 1,245 and 838 bp nucleotides with open reading frames of 933 and 651 nucleotides, respectively, and encoded for the complete amino acid sequences of mature proteins consisted of 288 (WCL1) and 195 (WCL3) residues, and signal sequences of 23 and 22 residues, respectively. WCLs were composed of three (for WCL1) or two (for WCL3) tandemly repeated homologous domains, which consisted of about 95 amino acid residues, and showed 91 and 93% sequence identities to STL1 and STL3, respectively. The mRNAs of WCL1 and WCL3 were detected exclusively in liver and ovary, respectively, however, neither a protein nor mRNA corresponding to STL2 could be identified in white-spotted charr. The phylogenetic tree of the sequences encoding carbohydrate recognition domains of 7 lectins from 4 species shows 5 functional clusters and their evolutional process. These results indicate that multiple L-rhamnose-binding isolectins have diverged by gene duplication and exon shuffling to play various biological roles in each species.

Rhamnose-binding lectins from steelhead trout (Oncorhynchus mykiss) eggs recognize bacterial lipopolysaccharides and lipoteichoic acid

The interaction between bacteria and three L-rham-nose-binding lectins, named STL1, STL2, and STL3, from steelhead trout (Oncorhynchus mykiss) eggs was investigated. Although STLs bound to most Gram-negative and Gram-positive bacteria, they agglutinated only Escherichia coli K-12 and Bacillus subtilis among the bacteria tested. The binding was inhibited by L-rhamnose. STLs bound to distinct serotypes of lipopolysaccharides (LPSs), and showed much higher binding activities to smooth-type LPSs of Escherichia coli K-12 and Shigella flexneri 1A than to their corresponding rough-type LPSs. STLs also bound to lipoteichoic acid (LTA) of Bacillus subtilis. These results indicate that STLs bound to bacteria by recognizing LPSs or LTA on the cell surfaces.