Cloning of six serpin genes and their responses to GCRV infection in grass carp (Ctenopharyngodon idella)

The survival, gene expression, and DNA methylation of Paralichthys olivaceus impacted by the decay of green tide and bacterial infection in both laboratory and field simulation experiments

The recurring appearance of Ulva prolifera green tides has become a pressing environmental issue, especially for marine transportation, tourism, and aquaculture in the stage of decomposition. An abundance of decaying U. prolifera leads to water acidification, hypoxia and pathogenic microorganism proliferation, threatening marine germplasm resources, particularly benthic organisms with weak escape ability. Epigenetic modification is considered to be one of the molecular mechanisms involved in the plastic adaptive response to environmental changes. However, few studies concerning the specific impact of decaying green tide on benthic animals at the epigenetic level. In this study, decomposing algal effluents of U. prolifera, sediments containing uncorrupted U. prolifera, pathogenic microorganism were considered as impact factors, to reveal the effect of decaying U. prolifera on marine economic benthic species, Paralichthys olivaceus, using both field and laboratory simulation experiments. Field simulation experiment showed higher mortality rates and serious histopathological damage than the laboratory simulation experiment. And both the decaying U. prolifera and the sediment containing U. prolifera were harmful to P. olivaceus. Genome-wide DNA methylation and transcription correlation analyses showed that the response of P. olivaceus to green tide stress and bacterial infection was mainly mediated by immune signaling pathways such as PI3K-Akt signaling pathway. DNA methylation regulates the expression of immune-related genes involved in the PI3K-Akt signaling pathway, which enables P. olivaceus to adapt to the adverse environmental stresses by resisting apoptosis. In summary, this research analyzed the potential role of P. olivaceus in decaying U. prolifera, which is of great significance for understanding the impact of decaying green tide on marine commercial fish and also provides some theoretical guidance for the proliferation and release of fish seedlings.

miR-2188-5p promotes GCRV replication by the targeted degradation of klf2a in Ctenopharyngodon idellus

Studies on host immunity evasion by aquatic viruses have largely focused on coding genes. There is accumulating evidence for the important biological functions of non-coding miRNAs in virus-host interactions. The regulatory functions of non-coding miRNAs in fish reovirus-host interactions remain unknown. Here, miR-2188-5p in grass carp (Ctenopharyngodon idellus), a miRNA specific to teleosts, was predicted to target the 3' UTR of the transcription factor klf2a. A correlation analysis and dual-luciferase reporter assay revealed that miR-2188-5p could induce the degradation of klf2a. The expression of miR-2188-5p induced the degradation of klf2a in a dose-dependent manner, suppressing the type I interferon response and promoting grass carp reovirus (GCRV) replication. As determined by a co-expression analysis, klf2a inhibited viral infection when miR-2188-5p was overexpressed. The targeted degradation of klf2a by miR-2188-5p could inhibit the type I interferon response and promote the replication of GCRV; however, this targeted degradation ability was insufficient to fully inhibit GCRV infection. These results provide novel insights into the regulatory effects and biological functions of non-coding miRNAs in fish-virus interactions.

Krüppel-like factor 2a (KLF2A) suppresses GCRV replication by upregulating serpinc1 expression in Ctenopharyngodon idellus kidney (CIK) cells

Krüppel-like factor 2a (KLF2A), a transcription factor of the krüppel-like family, is involved in regulating the immune molecules and is associated with viral infection. However, the function of KLF2A during viral infections in fish remains unclear. In this study, grass carp (Ctenopharyngodon idellus) was used to predict the target genes regulated by KLF2A. The results showed that the candidate target genes included four members of the serpin gene family (serpinb1l2, serpinc1, serpinh1a, and serpinh1b). Dual-luciferase experiments showed that klf2a positively regulates serpinc1 expression. Dose-dependent klf2a overexpression in C. idellus kidney (CIK) cells significantly upregulated the expression of serpinc1. Overexpressing klf2a or serpinc1 in CIK cells activated interferon responses and suppressed grass carp reovirus (GCRV) replication. Klf2a and serpinc1 co-expression inhibited GCRV replication. These results show that klf2a upregulates serpinc1 mRNA expression, promotes type 1 interferon responses, and suppresses GCRV infection. This study provides insights into the regulatory role and biological functions of KLF2A in host-virus interactions in fish.

Characterization of SR-B2a and SR-B2b genes and their ability to promote GCRV infection in grass carp (Ctenopharyngodon idellus)

Scavenger receptor class B type 2 (SR-B2) is a pattern recognition receptor involved in innate immunity in mammals; however, the immunological function of SR-Bs in fish remains unclear. In this study, the full-length cDNA sequences of SR-B2a and SR-B2b from grass carp (Ctenopharyngodon idellus) were cloned and designated as CiSR-B2a and CiSR-B2b. Multiple alignments and phylogenetic analyses deduced that CiSR-B2a and CiSR-B2b had the highest evolutionary conservation and were closely related to the zebrafish (Danio rerio) homologs, DrSR-B2a and DrSR-B2b, respectively. Both CiSR-B2a and CiSR-B2b were expressed in all the tested tissues, with the highest expression levels found in the hepatopancreas. In Ctenopharyngodon idellus kidney cells (CIK), CiSR-B2a and CiSR-B2b were mainly located in the cytoplasm, and a small amount located on the plasma membrane. After challenge with Grass Carp Reovirus (GCRV), the expression of CiSR-B2a and CiSR-B2b were significantly upregulated in the spleen (about 10.27 and 27.19 times higher than that at 0 day, p < 0.01). With CiSR-B2a or CiSR-B2b overexpressed in CIK, the relative copy number of GCRV in the cells was both significantly increased compared to that in the control group, indicating that CiSR-B2a and CiSR-B2b may be important proteins during the infection processes of GCRV.

Genome-wide identification, evolution of Krüppel-like factors (klfs) and their expressions during GCRV challenge in grass carp (Ctenopharyngodonidella)

The Krüppel-like factors (KLFs) are a family of transcription factors containing three highly conserved tandem zinc finger structures, and each member participates in multiple physiological and pathological processes. The publication of genome sequences and the application of bioinformatics tools have led to the discovery of numerous gene families in fishes. Here, 24 klf genes were re-annotated in grass carp. Subsequently, the number of klf family members were investigated in some representative vertebrate species. Then, a series of bioinformatics analysis showed that grass carp klfs in the same subfamily had similar genome structure patterns and conserved distribution patterns of motifs, which supported their molecular evolutionary relationships. Furthermore, the mRNA expression profiles showed that 24 grass carp klfs were ubiquitously expressed in 11 different tissues, and some of them displayed tissue-enriched expression patterns. Finally, the expressions of the evolutionarily expanded klf members (klf2a, 2b, 2l, 5a, 5b, 5l, 6a, 6b, 7a, 7b, 11a, 11b, 12a, 12b, 15 and 15l) during GCRV infection were also analyzed. The results suggested that grass carp klf genes with common evolutionary sources may share functional diversity and conservation. In conclusion, this study provides preliminary clues for further researches on grass carp klf members and their underlying transcriptional regulatory mechanisms during GCRV infection.

What Goes Wrong during Early Development of Artificially Reproduced European Eel Anguilla anguilla? Clues from the Larval Transcriptome and Gene Expression Patterns

Simple Summary

Closing the life cycle of the European eel in captivity is urgently needed to gain perspective for the commercial production of juvenile glass eels. Larvae are produced weekly at our facilities, but large variations in larval mortality are observed during the first week after hatching. Although much effort has been devoted to investigating ways to prevent early larval mortality, it remains unclear what the causes are. The aim of this study was to perform a transcriptomic study on European eel larvae in order to identify genes and physiological pathways that are differentially regulated in the comparison of larvae from batches that did not survive for longer than three days vs. larvae from batches that survived for at least a week up to 22 days after hatching (non-viable vs. viable larvae). In contrast to earlier published studies on European eel, we conclude that larvae exhibit immune competency. Non-viable larvae initiated an inflammatory and host protection immune response and tried to maintain osmoregulatory homeostasis. As a perspective, microbial control and salinity reduction might benefit eel larvae in terms of lower mortality and improved development by lowering the costs of immune functioning and osmoregulation.

Abstract

In eels, large variations in larval mortality exist, which would impede the viable production of juvenile glass eels in captivity. The transcriptome of European eel larvae was investigated to identify physiological pathways and genes that show differential regulation between non-viable vs. viable larvae. Expression of genes involved in inflammation and host protection was higher, suggesting that non-viable larvae suffered from microbial infection. Expression of genes involved in osmoregulation was also higher, implying that non-viable larvae tried to maintain homeostasis by strong osmoregulatory adaptation. Expression of genes involved in myogenesis, neural, and sensory development was reduced in the non-viable larvae. Expression of the major histocompatibility complex class-I (mhc1) gene, M-protein (myom2), the dopamine 2B receptor (d2br), the melatonin receptor (mtr1), and heat-shock protein beta-1 (hspb1) showed strong differential regulation and was therefore studied in 1, 8, and 15 days post-hatch (dph) larvae by RT-PCR to comprehend the roles of these genes during ontogeny. Expression patterning of these genes indicated the start of active swimming (8 dph) and feed searching behavior (15 dph) and confirmed immunocompetence immediately after hatching. This study revealed useful insights for improving larval survival by microbial control and salinity reduction.

B subunit of cholera toxin fused with VP7 from GCRV (grass carp reovirus) was expressed in E. coli and folds into an active protein

Grass carp reovirus (GCRV) is one of the most serious pathogens threatening grass carp (Ctenopharyngodon idella) production and results in high mortality in China. To obtain a genetically engineered oral vaccine against GCRV, the cholera toxin B subunit (CTB) of Vibrio cholerae was fused to VP7 (CTB-VP7) and transformed into BL21(DE3) for expression. SDS-PAGE and Western blotting showed that the purified rCTB-VP7 fusion protein (rCTB-VP7) was approximately 49.0 kDa. The monomeric nature of rCTB-VP7 through multistage purification showed a binding affinity for GM1, a receptor for biologically active CTB. rCTB-VP7 is not vulnerable to disassembly by SDS but is vulnerable to disassembly by 2-mercaptoethanol. rCTB-VP7 is stable and highly active at room temperature. The binding affinity experiment between rCTB-VP7 and GM1 also confirms the effects of acid and alkalinity in solution on the structure of rCTB-VP7. rCTB-VP7 bound to GM1 with different affinities under different temperatures and pH values. Prokaryotic expression of rCTB-VP7 was characterized by high expression and easy purification and had a strong binding force with GM1 at 37 °C and pH 7.4. Our results suggest that rCTB-VP7 has the potential as an oral vaccine for protection against GCRV in aquaculture.

Inducible Nitric Oxide Synthase (iNOS) Mediates Vascular Endothelial Cell Apoptosis in Grass Carp Reovirus (GCRV)-Induced Hemorrhage

Hemorrhage is one of the most obvious pathological phenomena in grass carp reovirus (GCRV) infection. The etiology of GCRV-induced hemorrhage is unclear. We found inducible nitric oxide synthase (iNOS) may relate to viral hemorrhage according to the previous studies, which is expressed at high levels after GCRV infection and is related to apoptosis. In this study, we aimed to investigate the mechanism of iNOS on apoptosis and hemorrhage at the cell level and individual level on subjects who were infected with GCRV and treated with S-methylisothiourea sulfate (SMT), an iNOS inhibitor. Cell structure, apoptosis rate, and hemorrhage were evaluated through fluorescence microscopy, Annexin V-FITC staining, and H&E staining, respectively. Cell samples and muscle tissues were collected for Western blotting, NO concentration measure, caspase activity assay, and qRT-PCR. iNOS-induced cell apoptosis and H&E staining showed that the vascular wall was broken after GCRV infection in vivo. When the function of iNOS was inhibited, NO content, apoptosis rate, caspase activity, and hemorrhage were reduced. Collectively, these results suggested iNOS plays a key role in apoptosis of vascular endothelial cells in GCRV-induced hemorrhage. This study is the first to elucidate the relationship between iNOS-induced cell apoptosis and GCRV-induced hemorrhage, which lays the foundation for further mechanistic research of virus-induced hemorrhage.

Molecular characterization, tissue distribution and functional analysis of galectin 1-like 2 in grass carp (Ctenopharyngodon idella)

Galectins, as an evolutionary conserved group of lectin superfamily, has the functions of pathogen recognition, anti-bacteria and anti-virus. In this study, a 405 bp cDNA sequence of galectin 1-like 2 (CiGal1-L2) was obtained from grass carp (Ctenopharyngodon idella), which encoded 134 amino acids with a predicted molecular mass of 15.143 kDa and an isoelectric point of 5.33. The sugar binding motifs (H-N-R, V-N and W--E-R) were detected in carbohydrate-binding domain (CRD). The amino acid sequence similarity showed that CiGal1-L2 was 40.30-42.54% and 66.42-81.20% similarity to mammalian and fish counterparts, respectively. The phylogenetic tree showed that CiGal1-L2 was clustered with fish galectin-1s and closely related to Cyprinus carpio. Real-time quantitative PCR (RT-qPCR) analysis revealed that CiGal1-L2 was widely expressed in all tested tissues. In addition, the expression of CiGal1-L2 was differentially up-regulated challenged with grass carp reovirus (GCRV), lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid (poly I:C). The fluorescence of CiGal1-L2-GFP was distributed in the cytoplasm and nucleus of HEK 293T cells and showed a trend of nuclear translocation after LPS and poly I:C treatment. Finally, the recombinant CiGal1-L2 (rCiGal1-L2) protein showed strong binding ability to LPS. In conclusion, the results provided further insight into the immune roles of galectin-1 in teleost.

The role of serpin protein on the natural immune defense against pathogen infection in Lampetra japonica

Serine protease inhibitors (serpins) are a large protein family that is involved in various physiological processes and is known to regulate innate immunity pathways. However, research for the functional study of serpins in lamprey is limited. In the present study, a serpin gene was cloned and characterized from Lampetra japonica at molecular, protein and cellular levels, named L-serpin which belongs to family F serine protease inhibitors (serpin family). The L-serpin includes a serpin domain in the N-terminus. The mRNA transcript of L-serpin was extensively expressed in kidney, supraneural body, intestine, liver, heart, gill and the highest expression in leukocytes. The mRNA expression level of L-serpin increased significantly after Vibrio anguillarum, Staphylocccus aureus and Poly I:C stimulation and dramatically peak at 8 h. It is demonstrated that the L-serpin protected cells from lethal Gram-negative endotoxemia through associating with inhibition of lipopolysaccharide (LPS)-triggered cell death and inflammatory factors expression. Surface plasmon resonance (SPR) and the microbe binding assay were used to determine that L-serpin interacts directly with LPS (KD = 6.14 × 10^-7 M). Furthermore, we confirmed L-serpin is a major inhibitor of complement activation by inactivating lamprey-C1q protein (KD = 2.06 × 10^-6 M). Taken together, these findings suggest that L-serpin is a endogenous anti-inflammatory factor to defend against Gram-negative bacterial challenge and involved in lamprey innate immunity.

Molecular characterization and functional activity of Prx1 in grass carp (Ctenopharyngodon idella)

Peroxiredoxin (Prx) family are known as an important antioxidant enzyme as the first line of defense against oxidative damage, and also involved in immune responses following viral and bacterial infection. Here, a full-length Prx1 cDNA sequence (CiPrx1) was cloned from grass carp (Ctenopharyngodon idella), which was 1029 bp, including a 5'-terminal untranslated region (UTR) of 121 bp, a 3'-UTR of 272 bp, an open reading frame of 600 bp encoding 199 amino acids with molecular weight of 22.21 kDa and isoelectric point of 6.30. CiPrx1 shares 80.8-99% protein sequence similarity with Prx1 of other fishes. The conserved peroxidase catalytic center "FYPLDFTFVCPTEI" and "GEVCPA" were observed in the sequence of CiPrx1; this indicated that it was a member of 2-Cys Prx. Subcellular localization of CiPrx1 was only strongly distributed in the cytoplasm. Quantitative real-time PCR (RT-qPCR) assays revealed that CiPrx1 mRNA was ubiquitously detected in all tested tissues, and the expression was comparatively high in liver, gill and spleen. Further, the expression of CiPrx1 can be induced by grass carp reovirus (GCRV), lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid (Poly I:C) infection in the different tissues. Moreover, the recombinant CiPrx1 (rCiPrx1) protein was found a potential antioxidant enzyme, that could inhibit DNA damage from oxidants. Altogether, our results imply that CiPrx1 is associated with defending against virus and bacteria pathogens and oxidants in grass carp.