Mandarin Fish Siniperca Chuatsi Research Articles

Molecular cloning and functional analyses of C–C motif chemokine ligand 3 (CCL3) in mandarin fish Siniperca chuatsi

Chemokines are critical molecules involved in immune reaction and immune system homeostasis, and some chemokines play a role in antiviral immunity. It is not known if the C–C motif chemokine ligand 3 (CCL3), a member of the CC chemokine family, possesses antiviral properties in fish. In this study, a ccl3 was cloned from the mandarin fish (Siniperca chuatsi), and it has an open reading frame (ORF) of 276 base pairs, which are predicted to encode a 91-amino acid peptide. Mandarin fish CCL3 revealed conserved sequence features with four cysteine residues and closely relationships with the CCL3s from other vertebrates based on the sequence alignment and phylogenetic analysis. The transcripts of ccl3 were notably enriched in immune-related organs, such as spleen and gills in healthy mandarin fish, and the ccl3 was induced in the isolated mandarin fish brain (MFB) cells following infection with infectious spleen and kidney necrosis virus (ISKNV). Moreover, in MFB cells, overexpression of CCL3 induced immune factors, such as IL1β, TNFα, MX, IRF1 and IFNh, and exhibited antiviral activity against ISKNV. This study sheds light on the immune role of CCL3 in immune response of mandarin fish, and its antiviral defense mechanism is of interest for further investigation.

Low-temperature immunization attenuates the residual virulence of orf074r gene-deleted infectious spleen and kidney necrosis virus: a candidate immersion vaccine.

Global aquaculture production yielded a record of 122.9 million tons in 2022. However, ~10% of farmed aquatic animal production is lost each year due to various infectious diseases, resulting in substantial economic waste. Therefore, the development of vaccines is important for the prevention and control of aquatic infectious diseases. Gene-deletion live attenuated vaccines are efficacious because they mimic natural pathogen infection and generate a strong antibody response, thus showing good potential for administration via immersion. However, most gene-deletion viruses still have residual virulence, and thus, gene-deletion immersion vaccines for aquatic viruses are rarely developed. In this study, an orf074r deletion strain (Δorf074r) of ISKNV with residual virulence was constructed, and an immunization process was developed to reduce its residual virulence at 22°C, thereby making it a potential immersion vaccine against ISKNV. Our work will aid in the development of an aquatic gene-deletion live-attenuated immersion vaccine.

Effects of chloride, sulfate, and bicarbonate stress on mortality rate, gill tissue morphology, and gene expression in mandarin fish (Siniperca chuatsi).

The mandarin fish Siniperca chuatsi is a freshwater fish that is endemic to East Asia. To study the different damages and molecular mechanisms caused by different salt (NaCl, Na2SO4, and NaHCO3) on Siniperca chuatsi, the fish were subjected to NaCl, Na2SO4, and NaHCO3 stresses with different concentration for 96 h for mortality assessment, moreover, the fish were exposed to these salt stresses with equal sodium ion concentration (Na+ = 210 mmol/L), then gill morphological changes were observed and gene expression was analyzed by high-throughput transcriptome sequencing and real-time quantitative PCR (qRT-PCR). The results showed that mandarin fish tolerated NaCl and Na2SO4 better than NaHCO3. NaHCO3 stress caused more damage to gill than NaCl and Na2SO4 stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses indicated that differentially expressed genes were enriched in damage and apoptosis upon NaHCO3 stress, whereas they were enriched in energy and immune-related pathways upon NaCl and Na2SO4 stress. Hub genes were different under all three stresses. MAPK pathway genes showed a trend in up-regulated expression under all salt stresses, but the expression patterns varied with time during salt exposure and freshwater recovery stage. Taken together, this study demonstrated the variation in the effects of NaCl, Na2SO4, and NaHCO3 stress on mandarin fish. The MAPK signaling pathway is important for regulating the response to salt stress.

The Inactivated ISKNV-I Vaccine Confers Highly Effective Cross-Protection against Epidemic RSIV-I and RSIV-II from Cultured Spotted Sea Bass Lateolabrax maculatus.

The genus Megalocytivirus of the family Iridoviridae is composed of two distinct species, namely, infectious spleen and kidney necrosis virus (ISKNV) and scale drop disease virus (SDDV), and both are important causative agents in a variety of bony fish worldwide. Of them, the ISKNV species is subdivided into three genotypes, namely, red seabream iridovirus (RSIV), ISKNV, and turbot reddish body iridovirus (TRBIV), and a further six subgenotypes, RSIV-I, RSIV-II, ISKNV-I, ISKNV-II, TRBIV-I, and TRBIV-II. Commercial vaccines derived from RSIV-I , RSIV-II and ISKNV-I have been available to several fish species. However, studies regarding the cross-protection effect among different genotype or subgenotype isolates have not been fully elucidated. In this study, RSIV-I and RSIV-II were demonstrated as the causative agents in cultured spotted seabass, Lateolabrax maculatus, through serial robust evidence, including cell culture-based viral isolation, whole-genome determination and phylogeny analysis, artificial challenge, histopathology, immunohistochemistry, and immunofluorescence as well as transmission electron microscope observation. Thereafter, a formalin-killed cell (FKC) vaccine generated from an ISKNV-I isolate was prepared to evaluate the protective effects against two spotted seabass original RSIV-I and RSIV-II. The result showed that the ISKNV-I-based FKC vaccine conferred almost complete cross-protection against RSIV-I and RSIV-II as well as ISKNV-I itself. No serotype difference was observed among RSIV-I, RSIV-II, and ISKNV-I. Additionally, the mandarin fish Siniperca chuatsi is proposed as an ideal infection and vaccination fish species for the study of various megalocytiviral isolates. IMPORTANCE Red seabream iridovirus (RSIV) infects a wide mariculture bony fish and has resulted in significant annual economic loss worldwide. Previous studies showed that the phenotypic diversity of infectious RSIV isolates would lead to different virulence characteristics, viral antigenicity, and vaccine efficacy as well as host range. Importantly, it is still doubted whether a universal vaccine could confer the same highly protective effect against various genotypic isolates. Our study here presented enough experimental evidence that a water in oil (w/o) formation of inactivated ISKNV-I vaccine could confer almost complete protection against RSIV-I and RSIV-II as well as ISKNV-I itself. Our study provides valuable data for better understanding the differential infection and immunity among different genotypes of ISKNV and RSIV isolates in the genus Megalocytivirus.

Molecular Characterization and Functional Analysis of Hypoxia-Responsive Factor Prolyl Hydroxylase Domain 2 in Mandarin Fish (Siniperca chuatsi).

With increased breeding density, the phenomenon of hypoxia gradually increases in aquaculture. Hypoxia is primarily mediated by the hypoxia-inducible factor 1 (HIF-1) signaling pathway. Prolyl hydroxylase domain proteins (PHD) are cellular oxygen-sensing molecules that regulate the stability of HIF-1α through hydroxylation. In this study, the characterization of the PHD2 from mandarin fish Siniperca chuatsi (scPHD2) and its roles in the HIF-1 signaling pathway were investigated. Bioinformation analysis showed that scPHD2 had the conserved prolyl 4-hydroxylase alpha subunit homolog domains at its C-terminal and was more closely related to other Perciformes PHD2 than other PHD2. Tissue-distribution results revealed that scphd2 gene was expressed in all tissues tested and more highly expressed in blood and liver than in other tested tissues. Dual-luciferase reporter gene and RT-qPCR assays showed that scPHD2 overexpression could significantly inhibit the HIF-1 signaling pathway. Co-immunoprecipitation analysis showed that scPHD2 could interact with scHIF-1α. Protein degradation experiment results suggested that scPHD2 could promote scHIF-1α degradation through the proteasome degradation pathway. This study advances our understanding of how the HIF-1 signaling pathway is regulated by scPHD2 and will help in understanding the molecular mechanisms underlying hypoxia adaptation in teleost fish.

A mandarinfish Siniperca chuatsi infection and vaccination model for SDDV and efficacy evaluation of the formalin-killed cell vaccine in yellowfin seabream Acanthopagrus latus

Scale drop disease virus (SDDV) is a distinct member in genus Megalocytivirus. Knowledge underlying pathogenesis of SDDV is still very limited. Here, a mandarinfish Siniperca chuatsi infection and vaccination model for SDDV was established. Artificial infection either by intraperitoneal or by intramuscular injection caused over 80% lethality to various sizes of mandarinfish juveniles. Cohabitation infection also resulted in over 70% lethality in the same infectious recycling water system. All data demonstrated that mandarinfish is a very highly susceptible fish species for SDDV. Real-time quantitative PCR showed that SDDV loads in infected-mandarinfish was the highest in spleen, followed by heart, gill, kidney, liver, muscle, intestines and brain, which was further confirmed by histopathology, immunofluorescence and immunochemistry. Histological analysis showed that although SDDV caused very high mortality to mandarinfish, its histopathology was not so typical as by ISKNV-infected mandarinfish. Formalin-killed cell (FKC) vaccines with 107.2 TCID50/0.1 mL, 106.9 TCID50/0.1 mL and 106.5 TCID50/0.1 mL SDDV antigens were prepared to immunize mandarinfish. As a result, the survivals of immunized fish were 100% (40/40), 97.5% (39/40) and 62.5% (25/40), respectively. By contrast, all un-immunized fish died upon SDDV challenge. Effectiveness of SDDV FKC vaccine was evaluated by immunizing 11,520 and 1038 yellowfin seabream and >90% protective effects were observed in both individual tests at 30 days post vaccination. Collectively, mandarinfish was confirmed as an ideal fish model for studying the infection and vaccination of SDDV, and MFF-1-based FKC vaccine renders highly effective protection against SDDV infection both in mandarinfish and yellowfin seabream.

Fishery Status and Rebuilding of Major Economic Fishes in the Largest Freshwater Lake in China Based on Limited Data

Poyang Lake, the largest freshwater lake in China, possesses abundant fishery resources, but its fish stock status is still unclear. In this work, the stock status of and fishing efforts of nine major economic fishes in the Poyang Lake were estimated from 2000 to 2019 with a catch-based maximum sustainable yield (CMSY) model based on catch and resilience data. It was further predicted whether the biomass of those fishes could be restored to support maximum sustainable yield (Bmsy) under the policy of “Ten years fishing moratorium in the Yangtze River”. The results showed that goldfish Carassius auratus, grass carp Ctenopharyngodon idella, and black carp Mylopharyngodon piceus suffered from higher fishing efforts and low biomass in the past 20 years; bighead carp Hypophthalmichthys nobilis, yellow catfish Tachysurus fulvidraco, and common carp Cyprinus carpio responded differently to their fishing efforts; silver carp Hypophthalmichthys molitrix, Amur catfish Silurus asotus, and mandarin fish Siniperca chuatsi were underexploited. Six species were overfished in 2019, and their biomass would be expected to recover for sustainable exploitation during the fishing moratorium, except for M. piceus. This study provided a case study of feasible freshwater fishery evaluation in limnetic ecosystems.

Molecular characterization and transcriptional conservation of N-myc-interactor, Nmi, by type I and type II IFNs in mandarin fish Siniperca chuatsi

N-myc-interactor (Nmi) belongs to interferon (IFN) stimulated genes (ISGs) and is involved in the regulation of physiological processes including viral infection, inflammatory response, apoptosis and tumorigenesis in mammals. However, the function of Nmi in teleost fish remains to be explored. In this study, an Nmi homologue was characterized from mandarin fish Siniperca chuatsi. The mandarin fish Nmi shares two conserved functional Nmi/IFP35 homology domains (NIDs) with mammalian Nmi protein in its C-terminal domain and a coiled coil region (CC) in its N-terminal domain, with its genomic DNA sequence consisting of nine exons and eight introns. Subcellular localization analysis shows that mandarin fish Nmi is a cytoplasmic protein and that its localization is dependent on the CC and NID1 regions. High and constitutive mRNA level of Nmi was observed in all examined tissues, with the highest level being observed in blood. In addition, the Nmi gene was significantly induced in various organs/tissues following the infection of infectious spleen and kidney necrosis virus (ISKNV), and its mRNA and protein level was also significantly induced in vitro after the treatment of IFNh, IFNc, as well as IFN-γ. The dual luciferase activity analysis indicated that the Nmi promoter was activated by the three type I IFNs through interferon-stimulated response element (ISRE) sites, and it can be also transcriptionally activated by IFN-γ via IRF1 which can activate the expression of Nmi through ISRE. Taken together, it is demonstrated in this study that the transcription of Nmi in mandarin fish can be regulated by type I and type II IFNs, thus confirming that Nmi in fish is also an ISG, and is involved in antiviral and IFN-induced innate immunity.

Functional characterization of four TIR domain-containing adaptors, MyD88, TRIF, MAL, and SARM in mandarin fish Siniperca chuatsi

Toll/interleukin-1 receptor (TIR) domain-containing adaptors, serve as pivotal signal transduction molecules in Toll-like receptor (TLR) signalling pathway to mediate downstream signalling cascades. In this study, four TIR-domain containing adaptors, MyD88, TRIF, MAL and SARM, were identified in mandarin fish Siniperca chuatsi, and they all contain TIR domains, of which MyD88 and SARM had high sequence homology with their vertebrate homologues. The expression analysis at mRNA level indicated that these genes were ubiquitously distributed in different tissues, being high in immune- and mucosa-related tissues such as head-kidney and intestine. The transcripts of these adaptor genes were up-regulated by poly(I:C) and LPS stimulation in isolated head-kidney lymphocytes (HKLs) of mandarin fish. Fluorescence microscopy revealed that all these molecules were localized in cytoplasm, and further investigations showed that the over-expression of MyD88, TRIF and MAL activated the NF-κB, ISRE or type Ι IFN promoters and inhibited SVCV replication, whereas their antiviral effects were significantly impaired when co-transfected with SARM. It was also confirmed by co-immunoprecipitation (Co-IP) that SARM interacts separately with MyD88, TRIF and MAL, and MAL interacts with MyD88. However, the regulatory mechanisms of these adaptors involved in signalling pathways of different TLRs should be of interest for further research.

Identification and expression analysis of sixteen Toll-like receptor genes, TLR1, TLR2a, TLR2b, TLR3, TLR5M, TLR5S, TLR7−9, TLR13a−c, TLR14, TLR21−23 in mandarin fish Siniperca chuatsi

Toll-like receptors (TLRs), as a family of pattern recognition receptors (PRRs), possess specific pathogen-related molecular pattern (PAMP) recognition spectrum in inducing immune responses. In this study, sixteen TLRs were identified and characterized in mandarin fish (Siniperca chuatsi). All these TLRs consist of leucine-rich repeats (LRRs), a transmembrane domain and a Toll/interleukin-I receptor (TIR) domain, with the exception of TLR5S which lacks TIR domain, and they can be clustered into five branches, i.e. TLR1 subfamily, TLR3 subfamily, TLR5 subfamily, TLR7 subfamily and TLR11 subfamily in phylogenetic tree. These TLR genes were expressed in all tested tissues and had high expression levels in immune-related tissues such as head-kidney and spleen or mucosa-related tissues such as intestine and pyloric caecum. The transcripts of TLR2a, TLR2b, TLR3, TLR13a, TLR14, TLR22 and TLR23 were all significantly up-regulated after stimulation with poly(I:C); TLR1, TLR2a, TLR2b, TLR3, TLR5M, TLR5S, TLR13a and TLR13b transcripts were all significantly up-regulated after stimulation with PGN; and TLR2a, TLR2b, TLR5M, TLR5S, TLR7, TLR8, TLR9, TLR13c, TLR14 and TLR22 transcripts were all significantly up-regulated after stimulation with LPS in isolated head kidney lymphocytes of mandarin fish. The findings in this study may provide a valuable basis for functional study on TLR genes in mandarin fish.

Transcriptome analysis of immune response against Siniperca chuatsi rhabdovirus infection in mandarin fish Siniperca chuatsi.

As one of the piscine rhabdoviruses, Siniperca chuatsi rhabdovirus (SCRV) has caused considerable losses to mandarin fish aquaculture industry. RNA-seq, as efficient transcriptome research method, has been widely used to study the immune response of fish to pathogens. This study reported the effect of SCRV infection at 0, 24 and 60hr on S.chuatsi at the transcriptome level. A total of 61,527 unigenes with high quality were obtained, and 3,095, 1,854 and 227 differentially expressed genes (DEGs) were labelled between the Sc24 and Sc0 groups, the Sc60 and Sc0 groups and the Sc60 and Sc24 groups, respectively. Genes involved in innate and adaptive immunity were highlighted. In Gene Ontology analysis, the DEGs that participated in immune response, innate immune response and the regulation of apoptotic process were identified as enriched classes. Kyoto Encyclopedia of Genes and Genomes pathway results indicated that most DEGs caused by SCRV infection were identified in the immune system (retinoic acid-inducible gene-I-like receptor/Toll-like receptor/nucleotide-binding oligomerization domain-like receptor/C-type lectin receptor signalling pathway), cellular processes, cell growth and death (p53 signalling pathway, cellular senescence, apoptosis and phagosome), and metabolism. Quantitative real-time PCR was used to further verify the expression levels of 15 immune-related DEGs. The transcriptome database obtained in this study provided further in-depth insight into the immune response of S.chuatsi against SCRV.

Comparative growth, feeding and reproduction of hatchery-reared and wild mandarin fish Siniperca chuatsi in a shallow Yangtze lake, China

Stocking hatchery-reared fish in natural shallow lakes is a common practice in Chinese fisheries. The success of these fisheries depends on the balance between the commercial value of the stock and the growth performance of stocked fish to rapidly reach commercial size. The mandarin fish Siniperca chuatsi has become a commercially important fishery in China. However, the performance of hatchery-reared mandarin fish (HMF) after release into natural environments and their interactions with wild mandarin fish (WMF) have received little attention. In this study, we compared the growth, feeding and reproduction of HMF with WMF in a shallow Yangtze lake. We found that 11 mo after release, the growth of HMF was significantly slower than that of WMF but rapidly caught up after 16-19 mo. This suggests that HMF may experience compensatory growth after 11 mo, which may be a result of a low reproductive investment compared to WMF. In addition, the trophic niche of HMF differed significantly from that of WMF, with a lower diversity of prey and a single dominant prey species. Furthermore, there was no significant diet overlap between HMF and WMF. Our findings demonstrated that the growth performance of HMF can equal or exceeded that of wild conspecifics, and that there was limited diet overlap with WMF, suggesting that the current stock enhancement programmes of releasing HMF can result in fish similar to that of WMF, with limited foraging competition.

Expression and antibacterial analysis of galectin-8 and -9 genes in mandarin fish, Siniperca chuatsi

Galectin-8 and galectin-9 belong to tandem repeat-type galectins, and in the present study, these two genes were cloned in mandarin fish Siniperca chuatsi. The open reading frame (ORF) of the mandarin fish galectin-8 and galectin-9 contains 942, and 1008 bp, encoding 313 and 335 amino acids, respectively. As a conserved feature, an N-terminal carbohydrate recognition domain (CRD), and a C-terminal CRD were observed in each of the two galectins in mandarin fish. In healthy fish, galectin-8 and -9 were constitutively expressed in all organs/tissues examined, and their expression can be induced following the stimulation of LPS and poly(I:C). It is obvious that galectin-8 had a higher increase at mRNA level following the stimulation of poly(I:C). It is further demonstrated that mandarin fish galectin-8 inhibited the growth of Flavobacterium columnare and Streptococcus agalactiae, and in addition to the two species of bacteria, galectin-9 inhibited also the growth of Edwardsiella piscicida, which provides the basis for further understanding their antibacterial role in immune response of mandarin fish.

Transcriptional and subcellular characterization of interferon induced protein-35 (IFP35) in mandarin fish, Siniperca chuatsi

Interferon (IFN)-stimulated genes (ISGs) exert multiple functions in immune system, and IFN-induced protein 35 (IFP35), which is a member of ISG, has been suggested to be involved in numerous cellular activities including the regulation of antiviral immunity in mammals. However, the role of IFP35 in fish innate immunity remains largely unknown. In the present study, we characterized the IFP35 gene in mandarin fish Siniperca chuatsi, which contains two conserved Nmi/IFP35 homology domains (NIDs) at C-terminus, but no leucine zipper motif, with its genomic DNA sequence consisting of eight exons and seven introns. High and constitutive mRNA level of IFP35 was observed in all examined tissues, with the highest level being observed in gills. Moreover, the IFP35 gene was significantly induced in vivo for 120 h following the infection of infectious spleen and kidney necrosis virus (ISKNV), and its mRNA and protein level was also significantly induced in vitro following the treatment of poly I:C, IFNh, IFNc, as well as IFN-γ. The subcellular localization results indicated that exogenous IFP35 protein was mainly located in cytoplasm, while endogenous IFP35 protein was transferred into, or aggregated around, the nucleus with the induction of poly I:C or IFNs. The dual luciferase activity analysis indicated that the IFP35 promoter was activated by type I and type II IFNs through ISRE site. It is considered that IFP35 in fish is involved in antiviral, as well as in IFN-induced innate immunity.

Production of neo‐male mandarin fish Siniperca chuatsi by masculinization with orally administered 17α-methyltestosterone

All-female populations of mandarin fish (Siniperca chuatsi) provide economic advantages in production because of the superior growth of females relative to males. The first step to produce all-female populations was artificially induced sex reversal of female mandarin fish; beginning at 10 dph, fish (undifferentiated) were treated with dietary 17α-methyltestosterone (MT) at 50 mg/kg and 100 mg/kg dosages for 2 months. The MT treatments successfully produced all-male stocks (male rate 100%), as compared with the control group (51.11%). The survival rate of MT-treated and control groups was not significantly different. MT did not alter fish growth over the course of the experiment to 240 dph. MT treatment promoted the development of testes, and it initially inhibited gonadosomatic index (GSI) and the levels of serum steroid hormone (T and E2). Nevertheless, at the 180 dph and 240 dph, the GSI and serum steroid hormone (T and E2) levels in MT treatment groups had no significant difference with control groups. The masculinization of mandarin fish was also demonstrated by the expression patterns of sex-specific genes, dmrt1, sox9, foxl2 and cyp19a1a; the gonads of MT-treated fish exclusively expressed male-specific dmrt1 and sox9 with no expression of female-specific foxl2 and cyp19a1a.

IRF11 regulates positively type I IFN transcription and antiviral response in mandarin fish, Siniperca chuatsi

In vertebrates, a total of eleven interferon (IFN) regulatory factors (IRFs), IRF1 to IRF11 are reported, with the conserved presence of IRF1 to IRF9 in all classes of vertebrates. However, IRF10 has been reported only in fish and birds, and IRF11 seems to be a fish specific IRF member. In this study, IRF11 in mandarin fish Siniperca chuatsi was found upregulated following virus infection, and IRF11 was localized constitutively in nucleus as revealed through immunofluorescence test. The overexpression and/or luciferase reporter assays showed that IRF11 can induce transcriptionally the ISRE activity, and the expression of type I IFNs, IFNc and IFNh, as well as the IFN-stimulated gene, Mx, thus inhibiting the Siniperca chuatsi rhabdovirus (SCRV) replication as indicated in the reduced expression of virus protein genes. It is thus suggested that IRF11 in mandarin fish and probably in other teleost fish can exert its antiviral effect through the upregulation of type I IFNs and ISGs.

Morphological and skeletal comparison and ecological adaptability of Mandarin fish Siniperca chuatsi and big-eye Mandarin fish Siniperca kneri

Most of the closely related fish species are similar in appearance, with slight differences. This study evaluated 35 morphological characteristic parameters and the number, shape, and spatial location of bones in the skull and vertebrae of the mandarin fish Siniperca chuatsi and big-eye mandarin fish Siniperca kneri. We can understand their ecological adaptability, compare their morphological and skeletal differences, and elucidate the relationship between their phenotypic trait differences and skeletal characteristics. The results were as follows: 1. The Student's t-test results revealed significant differences between S. chuatsi and S. kneri in terms of head depth, head back length, snout length, interorbital distance, distance of the eyes from the oral fissure, and width between the posterior trunk and base of the caudal fin. Principal component and discriminant analysis showed that the main morphological differences between S. chuatsi and S. kneri were in the eye position, head hump and body shape. 2. There was no significant difference in the number and shape of the skull and vertebrae between S. chuatsi and S. kneri, but they differed in spatial position. The terminus of the maxilla in S. chuatsi is located at the lower border of the postorbital bone, but at the anterior in S. kneri. The size of head hump is closely related to the spatial location of the splanchnocranium in S. chuatsi and S. kneri. The angles between the caudal vertebrae centrum and each of the following: the neural arch and spine; haemal arch and spine of S. chuatsi are larger than those of S. kneri. In conclusion, the morphological differences between S. chuatsi and S. kneri are closely related to the spatial position of skeleton. These phenotypic differences reflect the ecological adaptation of mandarin fish to different natural environments.

Molecular characterization and function of EGFR during viral infectionprocess in Mandarin fishSiniperca chuatsi

Epidermal growth factor receptor (EGFR) is a tyrosine kinase protein and plays a critical role in virus infection by modulating innate immunity. In this study, we cloned and sequenced the EGFR coding sequence of mandarin fish, designed as scEGFR, and explored its characteristics. scEGFR mRNA was widely expressed in the tested tissues of mandarin fish, and the higher mRNA levels were expressed in kidney and spleen. scEGFR expression was up-regulated in spleen and CPB cells at early stage of ISKNV and SCRV infection. Gefitinib (EGFR inhibitor) inhibited ISKNV and SCRV replication, and increased the expression of the interferon-stimulated genes (ISG). However the EGF (EGFR activator) promoted ISKNV and SCRV replication, and decreased the interferon-stimulated genes. Those results indicated that scEGFR and its signaling involved in ISKNV and SCRV infection, and EGFR activation negatively regulated the interferon response, providing a potential target for the development of new therapic strategy against ISKNV and SCRV.

GC-MS metabolomics reveals metabolic differences of the farmed Mandarin fish Siniperca chuatsi in recirculating ponds aquaculture system and pond

Siniperca chuatsi is currently one of the most important economic farmed freshwater fish in China. The aim of this study was to evaluate the metabolic profile of recirculating ponds aquaculture system (RAS)-farmed S. chuatsi. Gas Chromatography-Mass Spectrophotometry (GC-MS) metabolomic platform was used to comprehensively analyze the effects of recirculating ponds aquaculture system (RAS) on the Mandarin fish S. chuatsi metabolism. Database searching and statistical analysis revealed that there were altogether 335 metabolites quantified (similarity > 0) and 205 metabolites were identified by mass spectrum matching with a spectral similarity > 700. Among the 335 metabolites quantified, 33 metabolites were significantly different (VIP > 1 and p < 0.05) between RAS and pond groups. In these thirty-three metabolites, taurine, 1-Hexadecanol, Shikimic Acid, Alloxanoic Acid and Acetaminophen were higher in the pond group, while 28 metabolites were increased notably in the RAS group. The biosynthesis of unsaturated fatty acids, lysosome, tryptophan metabolism were recommended as the KEGG pathway maps for S. chuatsi farmed in RAS. RAS can provide comprehensive benefits to the effects of Siniperca chuatsi metabolism, which suggest RAS is an efficient, economic, and environmentally friendly farming system compared to pond system.

The roles of mandarin fish STING in innate immune defense against Infectious spleen and kidney necrosis virus infections

The mandarin fish Siniperca chuatsi is a cultured freshwater fish species that is popular in China because of its high market value. With the development of high-density cultural mode in mandarin fish, viral diseases such as Infectious spleen and kidney necrosis virus (ISKNV) are becoming increasingly serious. Stimulator of interferon genes (STING) is a central component in the innate immune response to cytosolic DNA and RNA derived from different pathogens. However, the roles of STING in innate immune response of mandarin fish remain unknown. In the present study, S. chuatsi STING (scSTING)-mediated host immune response against ISKNV infection was investigated. ScSTING transcription level increased remarkably in response to ISKNV infection, LPS, PMA, or poly (I:C) stimulation in mandarin fish fry (MFF-1) cells. Immunofluorescence results showed that scSTING localized majorly in the endoplasmic reticulum. scSTING overexpression remarkably increased the expression levels of scIFN-h, scMx, scISG15, scPKR, scViperin, scIL-1β, scIL-18, and scTNF-α genes. IFN-β-luciferase report assay results showed that the relative expressions of luciferin were remarkably increased in MFF-1 cells. Site mutation of serine (S) on C-terminus of scSTING showed that both S388 and S396 were important for mediated signaling. Furthermore, scSTING overexpression inhibited ISKNV infection, and knockdown of scSTING promoted ISKNV infection, indicating that scSTING could suppress ISKNV infection in MFF-1 cells. These observations suggested that the scSTING played an important role in innate immune against ISKNV infection. Our work would help elucidate the roles of teleost fish STING in innate immunity.