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

The gastric mucosa of Atlantic salmon (Salmo salar) is abundant in highly active chitinases

Atlantic salmon (Salmo salar) possesses a genome containing 10 genes encoding chitinases, yet their functional roles remain poorly understood. In other fish species, chitinases have been primarily linked to digestion, but also to other functions, as chitinase-encoding genes are transcribed in a variety of non-digestive organs. In this study, we investigated the properties of two chitinases belonging to the family 18 glycoside hydrolase group, namely Chia.3 and Chia.4, both isolated from the stomach mucosa. Chia.3 and Chia.4, exhibiting 95% sequence identity, proved inseparable using conventional chromatographic methods, necessitating their purification as a chitinase pair. Biochemical analysis revealed sustained chitinolytic activity against β-chitin for up to 24 h, spanning a pH range of 2 to 6. Moreover, subsequent in vitro investigations established that this chitinase pair efficiently degrades diverse chitin-containing substrates into chitobiose, highlighting the potential of Atlantic salmon to utilize novel chitin-containing feed sources. Analysis of the gastric matrix proteome demonstrates that the chitinases are secreted and rank among the most abundant proteins in the gastric matrix. This finding correlates well with the previously observed high transcription of the corresponding chitinase genes in Atlantic salmon stomach tissue. By shedding light on the secreted chitinases in the Atlantic salmon's stomach mucosa and elucidating their functional characteristics, this study enhances our understanding of chitinase biology in this species. Moreover, the observed capacity to effectively degrade chitin-containing materials implies the potential utilization of alternative feed sources rich in chitin, offering promising prospects for sustainable aquaculture practices.

Cross-species opsonic activity of zebrafish fish-egg lectin on mouse macrophages

Zebrafish Fish-egg lectin (zFEL) has been identified and proved to be a maternal factor with antibacterial and opsonic ability in fishes. In this study, we found that zFEL was capable of enhancing the phagocytosis of the bacteria by macrophages of mouse (RAW264.7 and mouse peritoneal macrophages), suggesting a cross-species function of zFEL in higher animals. Further studies showed that zFEL can active the antigen presentation ability by up-regulating the expression of CD80, CD86 and MHC II. Meanwhile, zFEL also promoted the polarization of macrophages to M1-type, which was confirmed by the increase of cytokines TNF-α and IL-6. The expression of p38 gene was up-regulated in macrophages preincubated with zFEL. Taken together, zFEL appears opsonic function in mammal macrophages and has potential application in immunomodulation.

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.

Effect of triploidy on liver gene expression in coho salmon (Oncorhynchus kisutch) under different metabolic states

BACKGROUND

Triploid coho salmon are excellent models for studying gene dosage and the effects of increased cell volume on gene expression. Triploids have an additional haploid genome in each cell and have fewer but larger cells than diploid coho salmon to accommodate the increased genome size. Studying gene expression in triploid coho salmon provides insight into how gene expression may have been affected after the salmonid-specific genome duplication which occurred some 90 MYA. Triploid coho salmon are sterile and consequently can live longer and grow larger than diploid congeners in many semelparous species (spawning only once) because they never reach maturity and post-spawning mortality is averted. Triploid fishes are also of interest to the commercial sector (larger fish are more valuable) and to fisheries management since sterile fish can potentially minimize negative impacts of escaped fish in the wild.

RESULTS

The vast majority of genes in liver tissue had similar expression levels between diploid and triploid coho salmon, indicating that the same amount of mRNA transcripts were being produced per gene copy (positive gene dosage effects) within a larger volume cell. Several genes related to nutrition and compensatory growth were differentially expressed between diploid and triploid salmon, indicating that some loci are sensitive to cell size and/or DNA content per cell. To examine how robust expression between ploidies is under different conditions, a genetic/metabolic modifier in the form of different doses of a growth hormone transgene was used to assess gene expression under conditions that the genome has not naturally experienced or adapted to. While many (up to 1400) genes were differentially expressed between non-transgenic and transgenic fish, relatively few genes were differentially expressed between diploids and triploids with similar doses of the transgene. These observations indicate that the small effect of ploidy on gene expression is robust to large changes in physiological state.

CONCLUSIONS

These findings are of interest from a gene regulatory perspective, but also valuable for understanding phenotypic effects in triploids, transgenics, and triploid transgenics that could affect their utility in culture conditions and their fitness and potential consequences of release into nature.

Shotgun proteomics of rainbow trout ovarian fluid

In the present study we used a shotgun proteomic approach to identify 54 proteins of rainbow trout ovarian fluid. The study has unravelled the identity of several proteins not previously reported in fish ovarian fluid. The proteome of trout ovarian fluid consists of diverse proteins participating in lipid binding and metabolism, carbohydrate and ion transport, innate immunity, maturation and ovulation processes. Most trout ovarian fluid proteins correspond to follicular fluid proteins of higher vertebrates, but 15% of the proteins were found to be different, such as those related to the immune system (precerebellin-like protein), proteolysis (myeloid cell lineage chitinase), carbohydrate and lipid binding and metabolism (vitellogenins), cell structure and shape (vitelline envelope protein gamma) and a protein with unknown functions (UPF0762 protein C6orf58 homologue). The present study could help in the decoding of the biological function of these proteins and in the discovery of potential biomarkers of oocyte quality.

Expression Analysis of Lily Type Lectin Isotypes in the Rock Bream, Oplegnathus fasciatus: in the Tissue, Developmental Stage and Viral Infection

Lectins belong to the pattern-recognition receptors (PRRs) class and play important roles in the recognition and elimination of pathogens via the innate immune system. Recently, it was reported that lily-type lectin-1 is involved when a pathogen attacks in the early immune response of fish. However, this study is limited to information that the lectin is involved in the innate immune response against viral infection. In the present study, the lily-type lectin-2 and -3 of Oplegnathus fasciatus (OfLTL-2 and 3) have been presented to be included B-lectin domain and two D-mannose binding sites in the amino acid sequence that an important feature for the fundamental structure. To investigate the functional properties of OfLTLs, the tissue distribution in the healthy rock bream and temporal expression during early developmental stage analysis are performed using quantitative real-time PCR. OfLTL-2 and 3 are predominantly expressed in the liver and skin, but rarely expressed in other organ. Also, the transcripts of OfLTLs are not expressed during the early developmental stage but its transcripts are increased after immune-related organs which are fully formed. In the challenge experiment with RBIV (rock bream iridovirus), the expression of OfLTLs was increased much more strongly in the late response than the early, unlike previously known. These results suggest that OfLTLs are specifically expressed in the immune-related tissues when those organs are fully formed and it can be inferred that the more intensively involved in the second half to the virus infection.

Molecular cloning and expression analysis of a new lily-type lectin in the rock bream, Oplegnathus fasciatus

A new lily-type lectin RbLTL was identified from rock bream (Oplegnathus fasciatus) and its expression analysed. In this study, a new lily-type lectin gene (RbLTL) was cloned from rock bream using expressed sequence tag (EST) analysis. The full-length RbLTL cDNA was encoding a 117-amino acid protein. The deduced amino acid sequence of RbLTL contained all of the conserved features crucial for its fundamental structure, including B-lectin domain and three d-mannose binding sites. RbLTL mRNA was predominately expressed in the gills, with reduced expression noted in intestine tissue. Expression analysis of time series sampled fertilized eggs revealed that expression gradually increased 1, 3, 12, and 24 h: However, expression decreased at 36 h. RbLTL expression was differentially up-regulated in rock bream gills challenged with Streptococcus iniae, Edwardsiella tarda and RSIV. Our results revealed that novel rock bream lily-type lectin may be an important molecule involved in pattern recognition and pathogen elimination in the innate immunity of rock bream.

Identification of a C-type lectin from tilapia (Oreochromis niloticus) and its functional characterization under low-temperature stress

C-type lectin, which plays an important role in fish innate immunity, was cloned from tilapia and its functional characterization under low-temperature stress is reported. Its ORF is 453 bp, encoding 150 amino acids, and has a 5'UTR of 83 bp, a 3'UTR of 559 bp, and a poly (A) tail. The tilapia C-type lectin genomic DNA was acquired with a length of 5714 bp, containing six exons and five introns. Its promoter sequence was cloned and has a length of 2251 bp. The highest promoter activity occurs in the regulatory region (-900 bp to -450 bp). A hemagglutination assay of recombinant tilapia C-type lectin protein showed positive hemagglutination of rabbit and tilapia erythrocytes. RT-qPCR and western blot assays showed that its expression in the liver, spleen, and intestine were clearly affected by low-temperature stress. Thus, tilapia C-type lectin appear to be affected by abiotic stress, as well as by biological stress.

Identification and functional characterization of fish-egg lectin in zebrafish

Fish-egg lectins (FELs) are identified in several species of fishes, but their activity and mode of action remain largely unknown in early life stages. Here we showed that zebrafish FEL (zFEL) was a maternal factor, which was capable of interacting with Gram-negative and Gram-positive bacteria and enhancing the phagocytosis of the bacteria by macrophages. Interestingly, microinjection of purified native zFEL into the embryos (resulting in the increase of zFEL in the embryos) markedly promoted the resistance of the embryos to the pathogenic Aeromonas hydrophila. Taken together, zFEL appears a maternal immune-relevant molecule capable of defending the developing embryos/larvae from pathogenic attacks.

Three-dimensional structure and ligand-binding site of carp fishelectin (FEL)

Carp FEL (fishelectin or fish-egg lectin) is a 238-amino-acid lectin that can be purified from fish eggs by exploiting its selective binding to Sepharose followed by elution withN-acetylglucosamine. Its amino-acid sequence and other biochemical properties have previously been reported. The glycoprotein has four disulfide bridges and the structure of the oligosaccharides linked to Asn27 has been described. Here, the three-dimensional structures of apo carp FEL (cFEL) and of its complex withN-acetylglucosamine determined by X-ray crystallography at resolutions of 1.35 and 1.70 Å, respectively, are reported. The molecule folds as a six-bladed β-propeller and internal short consensus amino-acid sequences have been identified in all of the blades. A calcium atom binds at the bottom of the funnel-shaped tunnel located in the centre of the propeller. Two ligand-binding sites, α and β, are present in each of the two protomers in the dimer. The first site, α, is closer to the N-terminus of the chain and is located in the crevice between the second and the third blades, while the second site, β, is located between the fourth and the fifth blades. The amino acids that participate in the contacts have been identified, as well as the conserved water molecules in all of the sites. Both sites can bind the two anomers, α and β, ofN-acetylglucosamine, as is clearly recognizable in the electron-density maps. The lectin presents sequence homology to members of the tachylectin family, which are known to have a function in the innate immune system of arthropods, and homologous genes are present in the genomes of other fish and amphibians. This structure is the first of a protein of this group and, given the degree of homology with other members of the family, it is expected that it will be useful to experimentally determine other crystal structures using the coordinates of cFEL as a search probe in molecular replacement.

Ontogeny of the immune system in Acipenserid juveniles

Sturgeon aquaculture has increased considerably worldwide but little is known about their immunological development and competence in early life stages. Culture of larvae is one of the most critical stages in intensive sturgeon farming, often associated with high mortality rates. The objective of this study was to characterize the developmental morphology (light and transmission electron microscopy, LM and TEM) of the meningeal myeloid tissue, spleen and thymus in Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) from hatching until 5 months old (2895°C·day (dd)). The spleen was first visible on 541 dd larvae LM sections and the other two immune organs in 768 dd samples (approximately 400 and 600 dd after onset of feeding). Generally, younger fish had significantly higher percentages of undifferentiated cells (meningeal myeloid tissue and spleen) and effective adaptive immune competence would not be expected in these fish on the onset of feeding, but further functional immune assessment is needed.

Methylated glycans as conserved targets of animal and fungal innate defense

Effector proteins of innate immune systems recognize specific non-self epitopes. Tectonins are a family of β-propeller lectins conserved from bacteria to mammals that have been shown to bind bacterial lipopolysaccharide (LPS). We present experimental evidence that two Tectonins of fungal and animal origin have a specificity for O-methylated glycans. We show that Tectonin 2 of the mushroom Laccaria bicolor (Lb-Tec2) agglutinates Gram-negative bacteria and exerts toxicity toward the model nematode Caenorhabditis elegans, suggesting a role in fungal defense against bacteria and nematodes. Biochemical and genetic analysis of these interactions revealed that both bacterial agglutination and nematotoxicity of Lb-Tec2 depend on the recognition of methylated glycans, namely O-methylated mannose and fucose residues, as part of bacterial LPS and nematode cell-surface glycans. In addition, a C. elegans gene, termed samt-1, coding for a candidate membrane transport protein for the presumptive donor substrate of glycan methylation, S-adenosyl-methionine, from the cytoplasm to the Golgi was identified. Intriguingly, limulus lectin L6, a structurally related antibacterial protein of the Japanese horseshoe crab Tachypleus tridentatus, showed properties identical to the mushroom lectin. These results suggest that O-methylated glycans constitute a conserved target of the fungal and animal innate immune system. The broad phylogenetic distribution of O-methylated glycans increases the spectrum of potential antagonists recognized by Tectonins, rendering this conserved protein family a universal defense armor.