Effects of dietary n-3 highly unsaturated fatty acids levels on growth, lipid metabolism and innate immunity in juvenile golden pompano (Trachinotus ovatus)

To investigate the effects of dietary n-3 highly unsaturated fatty acids (HUFA) levels on growth, lipid metabolism and innate immunity in juvenile golden pompano Trachinotus ovatus, a marine carnivorous teleost, a total of 450 fish (average body weight: 14.84 g) were randomly distributed into 18 cages at sea, each dietary group with three cages and respectively fed six diets (D1-D6) with 2.30% (D1), 0.64% (D2), 1.00% (D3), 1.24% (D4), 1.73% (D5), or 2.10% (D6) n-3 HUFA. Here, D1 with fish oil as lipid source was set as control, while D2-D6 used a mixed vegetable oil as lipid source and supplemented with docosahexaenoic acid- (DHA) and eicosapentaenoic acid- (EPA) enriched oils to adjust the n-3 HUFA levels. After 8 weeks feeding, the daily growth coefficient (DGC), specific growth rate (SGR) and feed efficiency ratio (FER) showed no significant difference among the six dietary groups (P > 0.05). The levels of EPA and DHA in serum and liver increased with the dietary n-3 HUFA levels. The activity of total superoxide disumutase (T-SOD) in serum of fish fed D4 and D5 were significantly higher than that of the other groups, whereas the opposite was true for serum IL-1β and IL-6 levels as well as liver malondialdehyde (MDA) content. The mRNA levels of genes related to hepatic lipid metabolism including sterol regulatory element-binding protein-1 (srebp-1), fatty acid binding protein 1 (fabp1), peroxisome proliferators-activated receptor alpha (pparα), elongase of very long-chain fatty acids 5 (elovl5) and fatty acyl desaturase 2 (fads2) were down-regulated in fish fed the diets with high n-3 HUFA levels, while those of apolipoprotein b 100 (aprob 100) and carnitine palmitoyl transferase 1 (cpt1) increased significantly as increasing n-3 HUFA levels up to 1.73% (D2-D5), but decreased in the 2.10% n-3 HUFA group (D6). In addition, the expression levels of genes related to innate immunity including interleukin-10 (il-10) and transforming growth factor β1 (tgf-β1) increased significantly when dietary n-3 HUFA increased from 0.64% to 1.73%, whereas the opposite was true for the expression levels of nuclear factor kappa-B (nf-κb), interleukin-1β (il-1β), interleukin-6 (il-6) and interleukin-8 (il-8). Overall, the results indicated that dietary n-3 HUFA at 1.24-1.73% (D4-D5) can effectively improve fatty acid profiles, lipid metabolism, antioxidant capacity and immune response of golden pompano.

Functional characterization, tissue distribution and nutritional regulation of the Elovl4 gene in golden pompano, Trachinotus ovatus (Linnaeus, 1758)

The elongases of very long-chain fatty acids (Elovls) are involved in the rate-limiting of the carbon chain elongation reaction in fatty acid (FA) biosynthesis in vertebrates. One member of the Elovls family, Elovl4, has been regarded as a critical enzyme involved in the biosynthesis pathway of polyunsaturated fatty acids (PUFAs). To explore the role of Elovl4 in PUFA synthesis in Trachinotus ovatus, the cDNA of the Elovl4b gene is cloned from T. ovatus (ToElovl4b). The ORF of ToElovl4b was 918 bp and encoded 305 amino acid (aa) protein sequences. Sequence alignment showed that the deduced amino acids contained significant structural features of the Elovl4 family, such as a histidine box motif (HXXHH), multiple transmembrane domains and an endoplasmic reticulum (ER) retention signal. Moreover, phylogenetic analysis revealed that ToElovl4b was highly conserved with that of Rachycentron canadum Elovl4b. Moreover, heterologous expression in yeast demonstrated that ToElovl4b could efficiently elongate 18:2n-6, 18:3n-6 and 20:5n-3 FAs up to 20:2n-6, 20:3n-6 and 22:5n-3, respectively. Furthermore, the tissue expression profile indicated that mRNA expression of ToElovl4b was higher in the gonads and brain than in other tissues. Additionally, nutritional regulation suggested the highest mRNA levels of ToElovl4b in liver and brain were under feeding with 1:1 FO-SO (fish oil, FO; soybean oil, SO) and 1:1 FO-CO (corn oil, CO)), respectively. These new insights were useful for understanding the molecular basis and regulation of LC-PUFA biosynthesis in fish.

Characterization and functional analysis of liver-expressed antimicrobial peptide-2 (LEAP-2) from golden pompano Trachinotus ovatus (Linnaeus 1758)

The liver-expressed antimicrobial peptide-2 (LEAP-2) is an important component of the innate immune defense system and plays an important role in resisting the invasion of pathogenic microorganisms. In this study, LEAP-2 from golden pompano (Trachinotus ovatus) was characterized and its expression in response to Photobacterium damselae was investigated. The full-length LEAP-2 cDNA was 1758 bp, which comprised a 5'-UTR of 250 bp, an ORF of 321 bp, and a 3'-UTR of 1187 bp, encoding 106 amino acids. LEAP-2 consisted of a conserved saposin B domain and four conserved cysteines that formed two pairs of disulphide bonds. The genomic organization of LEAP-2 was also determined and shown to consisted of three introns and two exons. The predicted promoter region of ToLEAP-2 contained several putative transcription factor binding sites. Quantitative real-time (qRT-PCR) analysis indicated that LEAP-2 was ubiquitously expressed in all examined tissues, with higher mRNA levels observed in the muscle, liver, spleen, and kidney. After P. damselae stimulation, the expression level of LEAP-2 mRNA was significantly upregulated in various tissues of golden pompano. In addition, SDS-PAGE showed that the molecular mass of recombinant LEAP-2 expressed in pET-32a was approximately 23 kDa. The purified recombinant protein showed antibacterial activity against Gram-positive and Gram-negative bacteria. Luciferase reporters were constructed for five deletion fragments of different lengths from the promoter region (-1575 bp to +251 bp), and the results showed that L3 (-659 bp to +251 bp) presented the highest activity, and it was therefore defined as the core region of the LEAP-2 promoter. The seven predicted transcription factor binding sites were deleted by using PCR technology, and the results showed that the mutation of the USF transcription factor binding site caused the activity to significantly decrease. The results indicate that golden pompano LEAP-2 potentially exhibits antimicrobial effects in fish innate immunity.

Toll-Like Receptor 5 of Golden Pompano Trachinotus ovatus (Linnaeus 1758): Characterization, Promoter Activity and Functional Analysis

Toll-like receptors (TLRs), as important pattern recognition receptors, represent a significant component of fish immune systems and play an important role in resisting the invasion of pathogenic microorganisms. The TLR5 subfamily contains two types of TLR5, the membrane form of TLR5 (TLR5M) and the soluble form of TLR5 (TLR5S), whose detailed functions have not been completely elucidated. In the present study, we first identified two genes, TLR5M (ToTLR5M) and TLR5S (ToTLR5S), from golden pompano (Trachinotus ovatus). The full-length ToTLR5M and ToTLR5S cDNA are 3644 bp and 2329 bp, respectively, comprising an open reading frame (ORF) of 2673 bp, encoding 890 amino acids, and an ORF of 1935 bp, encoding 644 amino acids. Both the ToTLR5s possess representative TLR domains; however, only ToTLR5M has transmembrane and intracellular TIR domains. Moreover, the transcription of two ToTLR5s was significantly upregulated after stimulation by polyinosinic:polycytidylic acid (poly (I:C)), lipopolysaccharide (LPS), and flagellin in both immune-related tissues (liver, intestine, blood, kidney, and skin) and nonimmune-related tissue (muscle). Furthermore, the results of bioinformatic and promoter analysis show that the transcription factors GATA-1 (GATA Binding Protein 1), C/EBPalpha (CCAAT Enhancer Binding Protein Alpha), and ICSBP (Interferon (IFN) consensus sequence binding protein) may play a positive role in moderating the expression of two ToTLR5s. Overexpression of ToTLR5M and ToTLR5S notably increases NF-κB (nuclear factor kappa-B) activity. Additionally, the binding assay revealed that two rToTLR5s can bind specifically to bacteria and pathogen-associated molecular patterns (PAMPs) containing Vibrio harveyi, Vibrio anguillarum, Vibrio vulnificus, Escherichia coli, Photobacterium damselae, Staphylococcus aureus, Aeromonas hydrophila, LPS, poly(I:C), flagellin, and peptidoglycan (PGN). In conclusion, the present study may help to elucidate the function of ToTLR5M/S and clarify their possible roles in the fish immune response to bacterial infection.

Insulin-like growth factor binding protein 3 gene of golden pompano (TroIGFBP3) promotes antimicrobial immune defense

Insulin-like growth factor binding protein 3 (IGFBP3), an important member of the IGFBP family, plays an important biological role in regulating cellular proliferation, differentiation, growth, apoptosis, and innate immunity. However, studies concerning IGFBP3 in teleosts are very limited and IGFBP3 function remains unclear. In this study, we conducted both in vivo and in vitro functional analyses of an IGFBP3 (TroIGFBP3) from the teleost fish golden pompano (Trachinotus ovatus). TroIGFBP3 is composed of 286 amino acid residues and shares a high amino acid sequence similarity (50.18%-93.71%) with other IGFBP3 sequences in humans and teleosts. TroIGFBP3 was widely distributed in various tissues, with the highest expression in the liver. TroIGFBP3 expression was significantly upregulated following Vibrio harveyi infection. The results of in vitro assays showed that TroIGFBP3 could stimulate macrophage activation and promote peripheral blood leukocytes (PBLs) proliferation. Meanwhile, TroIGFBP3 overexpression significantly inhibited bacterial infection in fish tissues, whereas TroIGFBP3 knockdown resulted in increased bacterial dissemination and colonization in golden pompano tissues in vivo. Furthermore, recombinant TroIGFBP3 could inhibit cellular proliferation and promote apoptosis of mouse tumor cells. Taken together, these results indicated that TroIGFBP3 plays a significant role in innate antibacterial immunity and provides a theoretical foundation for investigating the function of IGFBP3 in fish immune response.

Identification of heme oxygenase-1 from golden pompano (Trachinotus ovatus) and response of Nrf2/HO-1 signaling pathway to copper-induced oxidative stress

Heme oxygenase-1(HO-1) is a stress-inducible enzyme that mediates antioxidative and cytoprotective effects to maintain cellular redox homeostasis. In the present study, the full sequence of HO-1 was cloned from golden pompano(Trachinotus ovatus) by RT-PCR and RACE-PCR. The full cDNA sequence of HO-1 was 1349 bp in length which comprised of a 726 bp open reading frame (ORF) preceded by 262 bp 5'-untranslated region (UTR), and followed by a 360 bp 3'UTR, encoding 241 amino acid residues. Phylogenetic analysis revealed that HO-1 showed highest similarity to that of Takifugu rubripes. Tissue distribution analysis showed that the expression level of HO-1 was relatively high in heart, liver and spleen. A trial was conducted to investigate the response of Nrf2/HO-1 signaling pathway to oxidative stress induced by copper. The results showed that mRNA expression of NF-E2-related nuclear factor2 (Nrf2), Kelch-like-ECH-associated protein1 (keap1), superoxide dismutase (SOD), catalase (CAT), HO-1, NAD(P)H quinone oxidoreductase 1 (NQO1) and Glutathione peroxidase (GSH-PX) all significantly increased in copper treated group than that in the control group. This work provides new insight into the molecular mechanism underlying the Nrf2/HO-1 pathway in oxidative response in T. ovatus.

Fish TRAF2 promotes innate immune response to RGNNV infection

Tumour necrosis factor receptor-associated factors (TRAFs) are key regulatory proteins in the NF-κB signaling pathways. TRAF2 participates in the activation of both canonical and non-canonical NF-κB pathways, which are crucial for cell inflammation and cell survival. To elucidate its function in teleost fish, TRAF2 homologues of yellow grouper (Epinephelus awoara) and golden pompano (Trachinotus ovatus) have been cloned and characterized in this study. The open reading frame (ORF) of grouper TRAF2 (EaTRAF2) consists of 1563 nucleotides encoding a 521 amino acid protein with a predicted molecular mass of 58.70 kDa. The ORF of golden pompano TRAF2 (ToTRAF2) consists of 1563 nucleotides encoding a 521 amino acid protein with a predicted molecular mass of 58.66 kDa EaTRAF2 and ToTRAF2 share 99.23% and 99.42% identity with orange-spotted grouper (Epinephelus coioides) TRAF2 (EcTRAF2), respectively. Quantitative real-time PCR analysis indicated that the expression of EaTRAF2 was increased in grouper spleen (GS) cells after Red-spotted grouper nervous necrosis virus (RGNNV) infection; while the expression of ToTRAF2 was decreased in golden pompano brain (TOGB) cells after RGNNV infection. Both EaTRAF2 and ToTRAF2 were identified as a cytosolic protein and suggested to be associated with vesicles scattering in the cytoplasm. Both EaTRAF2 and ToTRAF2 enhanced RGNNV replication during viral infection in vitro. Further studies showed that EaTRAF2 and ToTRAF2 overexpression decreased the expression levels of interferon associated cytokines and pro-inflammatory factors. Taken together, these results are important for better understanding of the function of TRAF2 in fish and reveal its involvement in host response to immune challenges in RGNNV.

Cloning, molecular characterization, and nutritional regulation of fatty acid-binding protein family genes in gold pompanos (Trachinotus ovatus)

Fatty acid-binding protein (Fabp) is an important protein family involved in fatty acid uptake and deposition. Elucidating the function and regulation of fabps could contribute to the efficient production of biologically relevant fatty acids, such as highly unsaturated fatty acids (HUFAs), from fish. Herein, five genes from Trachinotus ovatus named fabp4, fabp6a, fabp6b, fabp7a, and fabp7b coding 133, 127, 118, 132, and 132 amino acid residues were cloned and sequenced. The effect of dietary HUFA on the expression of these genes was also investigated. Multiple protein sequence alignment showed that these Fabps shared high identity to their orthologs from other fish and mammals. Two conserved domains, lipocalin and lipocalin 7, were predicted in the deduced protein sequence of fabp4 and fabp7 paralogs, whereas fabp6 paralogs did not present the lipocalin domain. The adipose tissue, spleen, gill, and intestine showed the highest levels of fabp6b expression. In the brain, fabp6b was weakly expressed, whereas the expression of fabp7a was at its highest. Conversely, fabp7a showed a lower mRNA level than the other fabps in the liver and heart. In the dorsal muscle and kidney, fabp6a was the most abundantly expressed gene. Increasing dietary HUFA from 1.0% to 2.1% increased the gene expression of hepatic fabp4 and fabp6a gene expression but decreased gene expression in the dorsal muscle. Similarly, the expression of fabp7a in the dorsal muscle also declined in the 2.1% HUFA group. This study lays the groundwork for further studies focused on the physiological function and regulation of fish fabps.

Functional characterization of NK-lysin in golden pompano Trachinotus ovatus (Linnaeus 1758)

NK-lysin is an important part of the innate immune defence system and plays an important role in resisting the invasion of pathogenic microorganisms. In this study, NK-lysin from golden pompano (Trachinotus ovatus) was characterized and its expression in response to Photobacterium damselae was investigated. The full-length NK-lysin cDNA was 731 bp, which comprised a 5'-UTR of 63 bp, an ORF of 444 bp, and a 3'-UTR of 224 bp, and encoded 147 amino acids; NK-lysin consisted of a conserved saposin B domain and six conserved cysteines that formed three pairs of disulfide bonds. The genomic organization of NK-lysin was also determined and the gene consisted of four introns and five exons. The predicted promoter region of ToNK-lysin contained several putative transcription factor binding sites. Quantitative real-time (qRT-PCR) analysis indicated that ToNK-lysin was ubiquitously expressed in all examined tissues; the highest mRNA levels were observed in the skin, kidney and intestine, while the lowest expression level was detected in the stomach. After P. damselae stimulation, the expression level of NK-lysin mRNA was significantly upregulated in various tissues of golden pompano. In addition, SDS-PAGE showed that the molecular mass of recombinant NK-lysin expressed in pGEX-6P-1 was approximately 37 kDa. The purified recombinant protein showed antibacterial activity against gram-positive and gram-negative bacteria. The results indicate that golden pompano NK-lysin has potential antimicrobial roles in fish innate immunity.

Functional Analysis of IRF1 Reveals its Role in the Activation of the Type I IFN Pathway in Golden Pompano, Trachinotus ovatus (Linnaeus 1758)

Interferon (IFN) regulatory factor 1 (IRF1), a transcription factor with a novel helix–turn–helix DNA-binding domain, plays a crucial role in innate immunity by regulating the type I IFN signaling pathway. However, the regulatory mechanism through which IRF1 regulates type I IFN in fish is not yet elucidated. In the present study, IRF1 was characterized from golden pompano, Trachinotus ovatus (designated ToIRF1), and its immune function was identified to elucidate the transcriptional regulatory mechanism of ToIFNa3. The full-length complementary DNA (cDNA) of IRF1 is 1763 bp, including a 900-bp open reading frame (ORF) encoding a 299-amino-acid polypeptide. The putative protein sequence has 42.7–71.7% identity to fish IRF1 and possesses a representative conserved domain (a DNA-binding domain (DBD) at the N-terminus). The genomic DNA sequence of ToIRF1 consists of eight exons and seven introns. Moreover, ToIRF1 is constitutively expressed in all examined tissues, with higher levels being observed in immune-relevant tissues (whole blood, gill, and skin). Additionally, Cryptocaryon irritans challenge in vivo increases ToIRF1 expression in the skin as determined by Western blotting (WB); however, protein levels of ToIRF1 in the gill did not change significantly. The subcellular localization indicates that ToIRF1 is localized in the nucleus and cytoplasm with or without polyinosinic/polycytidylic acid (poly (I:C)) induction. Furthermore, overexpression of ToIRF1 or ToIFNa3 shows that ToIRF1 can notably activate ToIFNa3 and interferon signaling molecule expression. Promoter sequence analysis finds that several interferon stimulating response element (ISRE) binding sites are present in the promoter of ToIFNa3. Additionally, truncation, point mutation, and electrophoretic mobile shift (EMSA) assays confirmed that ToIRF1 M5 ISRE binding sites are functionally important for ToIFNa3 transcription. These results may help to illuminate the roles of teleost IRF1 in the transcriptional mechanisms of type I IFN in the immune process.

Genome-wide comparative analysis ofbone morphogenetic proteins: genomic structure, phylogeny, and expression patterns in the golden pompano,Trachinotus ovatus(Linnaeus, 1758)

Bone morphogenetic proteins (BMPs) play important roles in various physiological processes, especially during the formation and maintenance of various organs. In this study, we first obtained and characterized twenty BMP genes from the Trachinotus ovatus genome (designated as ToBMPs). Sequence alignment and phylogenetic analysis both indicated that the predicted amino acid sequences of ToBMP were highly conserved with corresponding homologs of other species. Moreover, a comparative analysis was performed with seven representative vertebrate genomes and found difference in number of BMP3 genes in different species, which three members, BMP3a, BMP3b-1, and BMP3b-2, existed in diploid T. ovatus, but there were four and two members in tetraploidized Cyprinus carpio (BMP3a-1, BMP3a-2, BMP3b-1, and BMP3b-2) and diploid Danio rerio (BMP3a and BMP3b), respectively. The amino acid alignment and genomic structure analysis of ToBMP3 also suggested that the BMP3 gene had expanded in T. ovatus. Furthermore, tissue expression patterns were assessed for the small intestine, liver, white muscle, brain, spleen, fin, gill, head kidney, stomach, blood, and gonads. It was discovered that BMP1, BMP2, BMP3a, BMP4, BMP6, BMP7b, BMP11, and BMP16 were ubiquitously expressed in all the tissues tested. To study the regulatory function of BMP in response to the intake of different types of food, the expression changes in BMP mRNAs were detected by qRT-PCR, and the results showed that the majority of the BMP genes had the highest mRNA levels in the small intestine and liver after ingesting pelleted feed. Our data provide a useful resource for further studies on how paralogous genes may have different expression profiles in T. ovatus.

Structural and expression analysis of golden pompano Trachinotus ovatus IRF5 and its role in regulation of type I IFN

The interferon regulatory factor 5 (IRF5) is a mediator of the type I IFN signalling pathways, thereby playing a key role in innate immunity. However, the detailed mechanism through which IRF5 regulates type I IFN in fish remains unclearly. In the present study, we first describe the identification of IRF5 (ToIRF5) from golden pompano (Trachinotus ovatus) and its features at the genomic sequence and expression level. The genomic DNA sequence consists of eight exons and seven introns. The full-length ToIRF5 cDNA is composed of 2, 059 bp and encodes for 499 amino acid polypeptides. The putative protein sequence shares 66.3%-82.9% identity to fish IRF5 and possesses three representative conserved domains (a DNA-binding domain (DBD) at the N-terminus, an IRF-associated domain (IAD), and a virus-activated domain (VAD) at the C-terminus) and one highly variable domain (middle region (MR)). Furthermore, the ToIRF5 transcript is constitutively expressed in all examined tissues, with higher levels observed in the immune relevant tissues. The mRNA levels of ToIRF5 are increased by polyinosinic: polycytidylic acid [poly (I: C)], lipopolysaccharide (LPS) and flagellin stimulation in the immune- and nonimmune-related tissues. The subcellular localization indicates that ToIRF5 is mainly localized in the cytoplasm with or without poly (I: C) induction. In addition, to explore whether ToIRF5 is a modulator of ToIFNa3, promoter analysis is performed. The region from -200 bp to +1 bp is identified as the core promoter by different truncated mutants of ToIFNa3. Mutation analyse declares that the activity of the ToIFNa3-5 promoter significantly decreases after targeted mutation of M2 binding sites. Moreover, overexpression of ToIRF5 in vitro memorably aggrandizes the expression of some IFN/IRF-based signalling pathway genes. These results provide new insights into the roles of teleost IRF5 in transcriptional mechanisms of type I IFN in the immunity process.

Skeletal anomalies in cultured golden pompano Trachinotus ovatus at early stages of development

Golden pompano Trachinotus ovatus (Linnaeus, 1758) is an important mariculture fish species with high commercial value in China. The present study thoroughly assessed the types and frequencies of skeletal deformities at the early developmental stages of golden pompano in an intensive aquaculture production system. Golden pompano (n = 500) were sampled 30 d posthatch (dph). The specimens were stained with Alcian blue and Alizarin red for the detection of deformities. The results of the study revealed that 77.2% of the specimens showed at least 1 spinal anomaly; most anomalies occurred in the prehemal region, and the most common deformity observed was vertebral fusion (37.4% incidence of deformities). The results of this study provide useful information for the early detection of skeletal deformities and for the optimization of fish fry breeding technologies.

Interferon regulatory factor 2 plays a positive role in interferon gamma expression in golden pompano, Trachinotus ovatus (Linnaeus 1758)

In fish, interferon (IFN) regulatory factor 2 (IRF2) is a regulator of the type I IFN-dependent immune response, thereby playing a crucial role in innate immunity. However, the specific mechanism by which IRF2 regulates type II IFN in fish remains unclear. In the present study, first, to analyse the potential role of golden pompano (Trachinotus ovatus) IRF2 (ToIRF2) in the immune response, the mRNA level of ToIRF2 was detected by quantitative real-time polymerase chain reaction (qRT-PCR) after parasite infection. ToIRF2 was upregulated at early time points in both local infection sites (skin and gill) and system immune tissues (liver, spleen, and head-kidney) after stimulation with Cryptocaryon irritans. Second, to investigate the modulation effect of ToIRF2 on type II IFN (interferon gamma, IFNγ) expression, a promoter analysis was performed using progressive deletion mutations of ToIFNγ. The expression level of IFNγ-5 was highest among the five truncated mutants in response to ToIRF2, indicating that the core promoter region was located from -189 bp to +120 bp, which included the IRF2 binding sites. Mutation analyses showed that the activity of the ToIFNγ promoter dramatically decreased after the targeted mutation of the M1, M2 or M3 binding sites. Additionally, electrophoretic mobile shift assay (EMSA) confirmed that IRF2 interacted with the M1 binding site in the ToIFNγ promoter region to dominate ToIFNγ expression. Finally, overexpressing ToIRF2 in vitro notably increased ToIFNγ and the transcription of several type II IFN/IRF-based signalling pathway genes. These results suggested that ToIRF2 might be involved in the host defence against C. irritans infection and contribute to a better understanding of the transcriptional mechanisms by which ToIRF2 regulates type II IFN in fish.

Genomic structure and characterization of growth hormone receptors from golden pompano Trachinotus ovatus and their expression regulation by feed types

In this study, sequence analysis showed that ToGHR1 and ToGHR2 encoded polypeptides of 577 and 588 amino acids, respectively. Bioinformatics analysis showed that both ToGHR1 and ToGHR2 contain FN3 domains and transmembrane domains, which have glycosylation and phosphorylation sites. The exons of ToGHR1 and exons 4-10 of ToGHR2 are homologous to exons 2 and 4-9 in Homo sapiens genes, respectively. Only 3 SSR sites in ToGHR1 have SSR polymorphisms, and ToGHR2 has no SSR polymorphisms. ToGHR1 and ToGHR2 have high homology with GHR1 and GHR2 of many fish by BLAST. qRT-PCR was used to examine the expression profile of ToGHR mRNA in 12 normal liver and intestine tissue samples from 3 feed-type groups. The results showed that ToGHR is expressed in all 12 tissues, especially liver and muscle tissues, which showed higher ToGHR expression than that in other tissues (p < 0.05). Experiments on feed-type groups may indicate that high levels of LC-PUFA in squid bait can promote ToGHR1 expression and simultaneously inhibit ToGHR2 expression in the liver tissue. In addition, the high levels of LC-PUFA in food could inhibit intestinal ToGHR1 expression, and the intermediate levels may promote intestinal ToGHR1 expression. However, the unsaturated fatty acid content in the food does not affect the expression of intestinal ToGHR2.

Growth, physiological, and molecular responses of golden pompano Trachinotus ovatus (Linnaeus, 1758) reared at different salinities

Golden pompano (Trachinotus ovatus) is a commercially important marine fish and is widely cultured in the coastal area of South China. Salinity is one of the most important environmental factors influencing the growth and survival of fish. The aims of this study are to investigate the growth, physiological, and molecular responses of juvenile golden pompano reared at different salinities. Juveniles reared at 15 and 25‰ salinity grew significantly faster than those reared at the other salinities. According to the final body weights, weight gain rate, and feed conversion ratio, the suitable culture salinity range was 15-25‰ salinity. The levels of branchial NKA activity showed a typical "U-shaped" pattern with the lowest level at 15‰ salinity, which suggested a lower energy expenditure on osmoregulation at this level of salinity. The results of this study showed that the alanine aminotransferase, aspartate aminotransferase, and cortisol of juveniles at 5‰ were higher than those of other salinity groups. Our results showed that glucose-6-phosphate dehydrogenase significantly increased at 5‰ and 35‰ salinity. Our study showed that osmolality had significant differences in each salinity group. GH, GHR1, and GHR2 had a wide range of tissue expression including the liver, intestine, kidneys, muscle, gills and brain. The expression levels of GH, GHR1 and GHR2 in the intestine, kidneys, and muscle at 15‰ salinity were significantly higher than those in other three salinity groups. Based on the growth parameters and physiological and molecular responses, the results of the present study indicated that the optimal salinity for rearing golden pompano was 21.36‰ salinity.

Transcriptome analysis of golden pompano (Trachinotus ovatus) liver indicates a potential regulatory target involved in HUFA uptake and deposition

Promoting highly unsaturated fatty acid (HUFA) uptake and deposition can improve nutritional value of farmed fish and reduce dietary fish oil addition. Previously, we found that the golden pompano Trachinotus ovatus liver HUFA content increased with the increasing of dietary HUFA. Therefore, we examined the common genes and pathways responsible for HUFA uptake and deposition in T. ovatus liver using transcriptome sequencing technology after feeding with either 1.0% or 2.1% HUFA for 8 weeks. Results showed that a total of 140 and 147 genes were significantly upregulated and downregulated, respectively. Five bile acid synthesis-related genes (CYP7A1, CYP8B1, AKR1D1, SCP2 and ACOT8), which are related to dietary fat emulsification were downregulated in 2.1% HUFA group, implying that the cholate synthesized through the classical pathway might be the main bile acid form in fat emulsification. Moreover, fatty acid transport protein (FATP)-6, fatty acid binding protein (FABP)-1, -4, and -6 increased with HUFA deposition, especially FATP6 and FABP4, suggesting that the two genes may be important mediators involved in HUFA uptake and deposition. KEGG analysis showed that most of the differential genes described above were involved in peroxisome proliferator activator receptor (PPAR) signaling pathway, and PPARγ increased with HUFA deposition, indicating that PPARγ might be a key regulator of HUFA uptake and deposition by regulating the genes involved in fatty acid emulsification and transport. This study focused on the liver, which is the center of intermediary metabolism, providing a comprehensive understanding of the molecular regulation of HUFA uptake and deposition in T. ovatus, which should be further investigated to develop potential measures to improve HUFA content.

Functional characterization of IRF8 regulation of type II IFN in golden pompano (Trachinotus ovatus)

Interferon regulatory factor 8 (IRF8) increases type I IFN transcription levels by binding to IFN promoters, thereby playing a role in innate immunity. Nevertheless, the detailed mechanism through which IRF8 regulates type II IFN in fish remains ambiguous. In the present study, two genes from the golden pompano (Trachinotus ovatus), IRF8 (ToIRF8) and IFN gamma (ToIFNγ), were identified in the IFN/IRF-based signalling pathway. The full-length ToIRF8 cDNA was composed of 2,141 bp and encoded a 421 amino acid polypeptide; the genomic DNA was 2,917 bp in length and consisted of 8 exons and 7 introns. The putative protein showed the highest sequence identity (90-92%) with fish IRF8 and possessed a DNA-binding domain (DBD), an IRF-association domain (IAD) and a nuclear localization signal (NLS) motif consistent with those of IRF8 in other vertebrates. Furthermore, the ToIRF8 transcripts were expressed in all examined tissues of healthy fish, with higher levels observed in the central nervous and immune relevant tissues. They were upregulated by polyinosinic acid: polycytidylic acid [poly (I: C)], lipopolysaccharide (LPS) and flagellin treatments in the blood, liver, intestine and kidney. The results from assays of subcellular localization showed that ToIRF8 was localized to the cytoplasm. Moreover, to investigate whether ToIRF8 was a regulator of ToIFNγ, a promoter analysis was performed using progressive deletion mutations of ToIFNγ. The results indicated that the region from -601 bp to -468 bp includes the core promoter. Mutation analyses indicated that the activity of the ToIFNγ promoter significantly decreased after the targeted mutation of the M1-M3 binding sites. Additionally, overexpressed ToIRF8 in vitro notably increased the expression of several IFN/IRF-based signalling pathway genes. These results suggest that IRF8 is vital in the defence of T. ovatus against bacterial infection and contributes to a better understanding of the transcriptional mechanisms of ToIRF8 on type II IFN in fish.

Comparative analysis of the expression patterns of IL-1β, IL-11, and IL-34 in golden pompano (Trachinotus ovatus) following different pathogens challenge

Interleukins (ILs) are a subgroup of cytokines, which are molecules involved in the intercellular regulation of the immune system. These cytokines have been extensively studied in mammalian models, but systematic analyses of fish are limited. In the current study, 3 IL genes from golden pompano (Trachinotus ovatus) were characterized. The IL-1β protein contains IL-1 family signature motif, and four long helices (αA - αD) in IL-11 and IL-34, which were well conserved. All 3 ILs clustered phylogenetically with their respective IL relatives in mammalian and other teleost species. Under normal physiological conditions, the expression of IL-1β, IL-11, and IL-34 were detected at varied levels in the 11 tissues examined. Most of the 3 ILs examined were highly expressed in liver, spleen, kidney, gill, or skin. Following pathogenic bacterial, viral, or parasitic challenge, IL-1β, IL-11, and IL-34 exhibited distinctly different expression profiles in a time-, tissue-, and pathogen-dependent manner. In general, IL-1β was expressed at higher levels following challenge with all pathogens examined than was observed for IL-11 and IL-34. Furthermore, Streptococcus agalactiae and Cryptocaryon irritans caused higher levels of IL-1β and IL-11 expression than Vibrio harveyi and viral nervous necrosis virus (VNNV). The increased expression of IL-34 caused by VNNV and C. irritans were higher than that caused by V. harveyi and S. agalactiae. These results suggest that these 3 ILs in T. ovatus may play different effect pathogen type specific responses.

Functional characterization of interferon regulatory factor 2 and its role in the transcription of interferon a3 in golden pompano Trachinotus ovatus (Linnaeus 1758)

Similar to mammals, fish possess interferon (IFN) regulatory factor 2 (IRF2)-dependent type I IFN responses. Nevertheless, the detailed mechanism through which IRF2 regulates type I IFNa3 remains largely unknown. In the present study, we first identified two genes from golden pompano (Trachinotus ovatus), IRF2 (ToIRF2) and IFNa3 (ToIFNa3), in the IFN/IRF-based signalling pathway. The open reading frame (ORF) sequence of ToIRF2 encoded 335 amino acids possessing four typical characteristic domains, including a conserved DNA-binding domain (DBD), an interferon association domain 2 (IAD2), a transcriptional activation domain (TAD), and a transcriptional repression domain (TRD). Furthermore, transcripts of ToIRF2 were significantly upregulated after stimulation by polyinosinic: polycytidylic acid [poly (I:C)], lipopolysaccharide (LPS) and flagellin in immune-related tissues (blood, liver, and head-kidney). Moreover, to investigate whether ToIRF2 was a regulator of ToIFNa3, promoter analysis was performed. The results showed that the region from -896 bp to -200 bp is defined as the core promoter using progressive deletion mutations of IFNa3. Additionally, ToIRF2 overexpression led to a clear time-dependent enhancement of ToIFNa3 promoter expression in HEK293T cells. Mutation analyses indicated that the activity of the ToIFNa3 promoter significantly decreased after targeted mutation of M4/5 binding sites. Electrophoretic mobile shift assays (EMSAs) verified that IRF2 interacted with the binding site of the ToIFNa3 promoter region to regulate ToIFNa3 transcription. Last, the promoter activity of ToIFNa3-2 was more responsive to treatment with poly (I:C) than LPS and flagellin. Furthermore, overexpression of ToIRF2 in vitro obviously increased the expression of several IFN/IRF-based signalling pathway genes after poly (I:C) abduction. In conclusion, the present study provides the first evidence of the positive regulation of ToIFNa3 transcription by ToIRF2 and contributes to a better understanding of the transcriptional mechanisms of ToIRF2 in fish.

Effects of dietary lipid sources on the intestinal microbiome and health of golden pompano (Trachinotus ovatus)

Replacement of fish oil (FO) with vegetable oils (VO) in diets is economically desirable for the sustainable development of the aquaculture industry. However, inflammation provoked by FO replacement limited its widely application in fish industry. In order to understand the mechanism of VO-induced inflammation, this study investigated the impact of different dietary vegetable oils on the intestinal health and microbiome in carnivorous marine fish golden pompano (Trachinotus ovatus). Three diets supplemented with fish oil (FO, rich in long-chain polyunsaturated fatty acids), soybean oil (SO, rich in 18:2n-6) and linseed oil (LO, rich in 18:3n-3), respectively, were fed on juvenile golden pompano for 8 weeks, and the intestinal histology, digestive enzymes activities, immunity and antioxidant indices as well as intestinal microbiome were determined. The results showed that dietary SO significantly impaired intestinal health, and decreased the number and height of intestinal folds, and muscle thickness, as well as the zonula occludens-1 (zo-1) mRNA expression in intestine. Moreover, the two dietary VO significantly decreased the amylase and lipase activities in intestine, and reduced the trypsin activity in the dietary SO group. Furthermore, the two VO diets increased intestinal acid phosphatase (ACP) activity, while intestinal lysozyme (LZM) activity and serum diamine oxidase (DAO) activity in the SO group were also significantly increased (P < 0.05). Analysis of the intestinal microbiota showed that the two VO diets significantly increased the abundance of intestinal potentially pathogenic bacteria (Mycoplasma and Vibrio) and decreased proportions of intestinal probiotics (Bacillus and Lactococcus), especially in the dietary SO group. These results indicate that complete replacement of FO with VO in diets would induce intestinal inflammation and impair intestinal function, which might be due to changes in intestinal microbiota profiles, and that dietary SO would have a more negative effect compared to dietary LO on intestinal health in T. ovatus.

(Myxozoa: Ceratomyxidae) infecting the gallbladder of the cultured Trachinotus ovatus (Perciformes: Carangidae) in Batam Island, Indonesia

A new coelozoic myxozoan species, Ceratomyxa batam n. sp., was identified in cultured carangid fish, Trachinotus ovatus (Perciformes: Carangidae), in waters off Batam Island of Indonesia. The bi- and trivalved spores were observed in the gallbladder of T. ovatus. Mature bivalved spores of C. batam n. sp. were transversely elongated and narrowly crescent in shape, 3.8 ± 0.36 (2.7-4.6) μm long and 19.2 ± 1.75 (16.2-22.0) μm thick. Two sub-spherical polar capsules were 2.3 ± 0.18 (2.0-2.8) μm long and 2.6 ± 0.16 (2.3-2.9) μm wide. Prevalence was 72.2% in 72 examined T. ovatus according to evaluations dating from November 2016. The maximum likelihood phylogenetic tree based on small subunit rDNA sequence showed similarity with Ceratomyxa robertsthomsoni and Ceratomyxa thalassomae found in Australia. This is the first report of Ceratomyxa species identified in a seawater fish at Batam Island, Indonesia.

Molecular characterization of toll-like receptor 14 from golden pompano Trachinotus ovatus (Linnaeus, 1758) and its expression response to three types of pathogen-associated molecular patterns

Toll-like receptors (TLRs) play crucial roles in the host immune system, including recognizing invading pathogenic microbes and triggering immune reactions. Toll-like receptor 14 (TLR14) has been identified in several fish species, but its function requires further study. In this study, TLR14 (designed as ToTLR14) from golden pompano (Trachinotus ovatus), was characterized and investigated its expression responses to three types of pathogen-associated molecular patterns. The full-length ToTLR14 cDNA was 3191 bp, and the deduced protein consisted of 876 amino acids. The ToTLR14 protein included 5 leucine rich repeat (LRR) domains, a C-terminal LRR domain in the extracellular region, a transmembrane domain and a Toll/interleukin (IL)-1 receptor (TIR) domain in the cytoplasmic region, which fits with the typical TLR domain architecture. The genomic organization of ToTLR14 was also identified and consisted of four introns and five exons. The predicted promoter region of ToTLR14 contained several putative transcription factor binding sites. Phylogenetic analysis showed that ToTLR14 was clustered into the TLR1 subfamily clade. Quantitative real-time (qRT-PCR) analysis indicated that ToTLR14 were ubiquitously expressed in all examined tissues, with higher mRNA levels observed in the skin, kidney and intestine, while the lowest level was detected in the stomach. After injection with polyinosinic:polycytidylic acid [poly(I:C)], flagellin or lipopolysaccharides (LPS), the expression level of ToTLR14 mRNA were significantly upregulated in various tissues of golden pompano. These results indicate that ToTLR14 may play an important role in systemic as well as mucosal defence after viral and bacterial stimulation.

TroCCL4, a CC chemokine of Trachinotus ovatus, is involved in the antimicrobial immune response

CC chemokines are a large subfamily of chemokines that play an important role in the innate immune system. To date, several CC chemokines have been identified in fish species; however, the activities and functions of these putative chemokines remain ambiguous in teleosts, especially in the golden pompano, Trachinotus ovatus. Here, we characterized CC chemokine ligand 4 from T. ovatus (TroCCL4) and studied its functions. TroCCL4 contains a 294 bp open reading frame that encodes a putative peptide comprising 97 amino acids. TroCCL4 shares a high amino acid sequence similarity of 31.11%-78.35% with other CC chemokines sequences in humans and teleosts and has four cysteine residues that are conserved among other CC chemokines. TroCCL4 is also related to the macrophage inflammatory protein (MIP) group of CC chemokines. TroCCL4 expression was most abundant in immune organs and significantly upregulated in a time-dependent manner following Edwardsiella tarda infection. Recombinant TroCCL4 (rTroCCL4) induced the migration of peripheral blood leukocytes and the cellular proliferation of head kidney lymphocytes. In addition, rTroCCL4 inhibited the growth of Escherichia coli and E. tarda, indicating an antimicrobial function. Furthermore, the results of in vivo analysis showed that TroCCL4 overexpression in T. ovatus significantly enhanced macrophage activation; upregulated the gene expression of interleukin 1-β (IL-1β), interleukin 15 (IL15), interferon-induced Mx protein (Mx), tumor necrosis factor α (TNFα), complement C3, and major histocompatibility complex (MHC) class Iα and class IIα; and protected against bacterial infection in fish tissues. In contrast, knockdown of TroCCL4 expression resulted in increased bacterial dissemination and colonization in fish tissues. Taken together, our results provide evidence indicating that TroCCL4 has the ability to stimulate leukocytes and macrophages and enhance host immunity to defend against bacterial infection.

A β-defensin gene of Trachinotus ovatus might be involved in the antimicrobial and antiviral immune response

Defensins are a group of small cationic and cysteine-rich peptides that are important components of the innate immune system. However, studies on defensins in teleosts are very limited, particularly studies on defensin functions through in vivo assays. In this study, we cloned and identified one β-defensin (TroBD) the golden pompano, Trachinotus ovatus, and analyzed the functions of TroBD in both in vivo and in vitro assays. TroBD is composed of 63 amino acids and shares high sequence identities (27.27-98.41%) with known β-defensins of other teleosts. The protein has a signature motif of six conserved cysteine residues within the mature peptide. The expression of TroBD was most abundant in the head kidney and spleen and was significantly upregulated following infection by Vibrio harveyi and viral nervous necrosis virus (VNNV). Purified recombinant TroBD (rTroBD) inhibited the growth of V. harveyi, and its antimicrobial activity was influenced by salt concentration. TroBD was found to have a chemotactic effect on macrophages in vitro. The results of an in vivo study demonstrated that TroBD overexpression/knockdown in T. ovatus significantly reduced/increased bacterial colonization or viral copy numbers in tissues. Taken together, these results indicate that TroBD plays a significant role in both antibacterial and antiviral immunity and provide new avenues for protection against pathogen infection in the aquaculture industry.

Identification of Fatty Acid Desaturase 6 in Golden Pompano Trachinotus Ovatus (Linnaeus 1758) and Its Regulation by the PPARαb Transcription Factor

Fatty acid desaturases are rate-limiting enzymes in long-chain polyunsaturated fatty acid biosynthesis. The transcription factor peroxisome proliferator-activated receptor alpha b (PPARαb) regulates lipid metabolism in mammals, however, the mechanism whereby PPARαb regulates fatty acid desaturases is largely unknown in fish. In this study, we report the full length cDNA sequence of Trachinotus ovatus fatty acid desaturase, which encodes a 380 amino acid polypeptide, possessing three characteristic histidine domains. Phylogenetic and gene exon/intron structure analyses showed typical phylogeny: the T. ovatus fatty acid desaturase contained a highly conserved exon/intron architecture. Moreover, functional characterization by heterologous expression in yeast indicated that T. ovatus desaturase was a fatty acid desaturase, with Δ4/Δ5/Δ8 Fad activity. Promoter activity assays indicated that ToFads6 desaturase transcription was positively regulated by PPARαb. Similarly, PPARαb RNA interference decreased ToPPARαb and ToFads6 expression at the mRNA and protein levels in a time-dependent manner. Mutation analyses showed that the M2 binding site of PPARαb was functionally important for protein binding, and transcriptional activity of the ToFads6 promoter was significantly decreased after targeted mutation of M2. Electrophoretic mobile shift assays confirmed that PPARαb interacted with the binding site of the ToFads6 promoter region, to regulate ToFads6 transcription. In summary, PPARαb played a vital role in ToFads6 regulation and may promote the biosynthesis of long-chain polyunsaturated fatty acids by regulating ToFads6 expression.

The Transcriptional Factor PPARαb Positively Regulates Elovl5 Elongase in Golden Pompano Trachinotus ovatus (Linnaeus 1758)

The nuclear peroxisome proliferator-activated receptors (PPARs) regulate the transcription of elongases of very long-chain fatty acids (Elovl), which are involved in polyunsaturated fatty acid (PUFA) biosynthesis in mammals. In the present study, we first characterized the function of Elovl5 elongase in Trachinotus ovatus. The functional study showed that ToElovl5 displayed high elongation activity toward C18 and C20 PUFA. To investigate whether PPARαb was a regulator of Elovl5, we also reported the sequence of T. ovatus PPARαb (ToPPARαb). The open reading frame (ORF) sequence encoded 469 amino acids possessing four typical characteristic domains, including an N-terminal hypervariable region, a DNA-binding domain (DBD), a flexible hinge domain and a ligand-binding domain (LBD). Thirdly, promoter activity experiments showed that the region from PGL3-basic-Elovl5-5 (-146 bp to +459 bp) was defined as the core promoter by progressive deletion mutation of Elovl5. Moreover, PPARαb overexpression led to a clear time-dependent enhancement of ToElovl5 promoter expression in HEK 293T cells. Fourth, the agonist of PPARαb prominently increased PPARαb and Elovl5 expression, while PPARαb depletion by RNAi or an inhibitor was correlated with a significant reduction of Elovl5 transcription in T. ovatus caudal fin cells (TOCF). In conclusion, the present study provides the first evidence of the positive regulation of Elovl5 transcription by PPARαb and contributes to a better understanding of the transcriptional mechanism of PPARαb in fish.

Genomic structure and molecular characterization of Toll-like receptors 1 and 2 from golden pompano Trachinotus ovatus (Linnaeus, 1758) and their expression response to three types of pathogen-associated molecular patterns

Toll-like receptors (TLRs) play an essential role in the immune response. Here two Toll-like receptors from golden pompano (Trachinotus ovatus), ToTLR1 and ToTLR2, were characterized, the full-length cDNAs were 3126 bp and 7430 bp, and the deduced proteins consisted of 801 and 825 amino acids, respectively. ToTLR1 and ToTLR2 both contained the typical TLR domain architecture including signal peptide, leucine rich repeat (LRR), C-terminal LRR domain at the extracellular region and Toll/interleukin (IL)-1 receptor (TIR) domain in the cytoplasmic region. ToTLR1 only had one intron and two exons, but ToTLR2 consisted of twelve introns and thirteen exons. The promoters of ToTLR1 and ToTLR2 contained several putative transcription factor binding sites. Phylogenetic analysis showed that ToTLR1 and ToTLR2 were clustered into the clade of TLR1 and TLR2, respectively. Tissues distribution analysis indicated that both genes were ubiquitously expressed in all examined tissues, with higher expression levels observed in blood, head-kidney and spleen. After injection with poly inosinic:cytidylic [poly(I:C)], flagellin and lipopolysaccharides (LPS), ToTLR1 and ToTLR2 mRNAs were significantly up-regulated in the immune related tissues, indicating the possible the role of ToTLR1 and ToTLR2 in defense against pathogenic microbes. Further research should be carried out to identify ligands of fish TLR1 and TLR2 in order to understand the function of these receptors.

MHC class IIα polymorphism and its association with resistance/susceptibility to Vibrio harveyi in golden pompano (Trachinotus ovatus)

The major histocompatibility complex (MHC) plays an important role in the vertebrate immune response to antigenic peptides, and it is essential for recognizing foreign pathogens in organisms. In this study, MHC class IIα (Trov-MHC IIα) from the golden pompano (Trachinotus ovatus) was first cloned and identified. The gene structure of Trov-MHC IIα was contained four exons and three introns. High levels of polymorphism were found in the exon 2 of Trov-MHC IIα. A total of 29 different MHC class IIα alleles with high polymorphism were identified from 80 individuals. The ratio of non-synonymous substitutions (dN) to synonymous substitutions (dS) was 3.157 (>1) in the peptide binding regions (PBRs) of Trov-MHC IIα, suggesting positive balancing selection. Six alleles were selected to analyze the association between alleles and resistance/susceptibility to Vibrio harveyi in golden pompano. The results showed that Trov-DAA*6401 and Trov-DAA*6702 alleles were associated with the resistance to V. harveyi in golden pompano, while alleles Trov-DAA*6304 and Trov-DAA*7301 were associated with the susceptibility to V. harveyi in golden pompano. This study confirmed the association between alleles of MHC class IIα and disease resistance, and also detected some alleles which might be correlated with high V. harveyi-resistance. These disease resistance-related MHC alleles could be used as potential genetic markers for molecular marker-assisted selective breeding in the golden pompano.

Establishment of a new fish cell line from the caudal fin of golden pompano Trachinotus ovatus and its susceptibility to iridovirus

A new cell line derived from the caudal fin of golden pompano Trachinotus ovatus (TOCF) was successfully established and characterized. TOCF cells grew well at 28° C in L-15 medium supplemented with 10% foetal bovine serum (FBS). The cell line has been subcultured in more than 100 passages. Molecular characterization of 18S ribosomal (r)RNA and cytochrome oxidase subunit 1 (COI) confirmed that the TOCF cells were derived indeed from T. ovatus. TOCF cells have a modal chromosome number of 54. It was further showed that TOCF cells were transfected successfully with pEGFP-N3 and pDsRED-N1 plasmid, suggesting that TOCF cells could be used to research gene functions in vitro. Viral susceptibility tests showed that TOCF cells were susceptible to Singapore grouper iridovirus (SGIV), observed by the occurrence of the cytopathic effect (CPE) with the formation of inclusion bodies. In addition, the expression of major capsid protein (MCP) gene of SGIV changed during virus infection in TOCF cells. Thus, our present results described the characteristic of a TOCF cell line that could be a valuable tool for genetic manipulation, as well as isolation and propagation of iridovirus studies.

Genomic structure, expression pattern and polymorphisms of GILT in golden pompano Trachinotus ovatus (Linnaeus 1758)

The interferon-g-inducible lysosomal thiol reductase (GILT) plays a significant character in the processing and presentation of MHC class II restricted antigen (Ag) by catalyzing disulfide bond reduction in mammals. To explore the function of GILT in the immune system of fish, we cloned a GILT gene homologue from Trachinotus ovatus, the full-length cDNA of GILT, which consisted of 2, 747 bp with a 771 bp open reading frame, encoding a protein of 256 amino acids. Moreover, similar to other species GILT gene, 7 exons and 6 introns were identified in T. ovatus, the deduced protein also possessed a representative characteristic of known GILT proteins. The result of real-time quantitative PCR showed that GILT mRNA was dramatically expressed in immune-associated tissues, such as spleen (p < 0.01) and kidney (p < 0.05). Bacterial challenge revealed that GILT mRNA level remarkably up-regulation in liver, spleen, kidney and intestine after induction with Photobacterium damsela. Furthermore, based on cloned sequences and genome BLAST, only one SNP site (ToGILT-S1-g.148C>G) was identified, and the allele C was significantly associated with high-susceptibility (HS) group, nevertheless, the allele G was dramatically associated with high-resistance (HR) group, indicating potential application for disease resistant breeding selection in T. ovatus.

Effects of dietary dandelion extract on intestinal morphology, antioxidant status, immune function and physical barrier function of juvenile golden pompano Trachinotus ovatus

Intestinal morphology, antioxidant status, immune function and tight junction proteins mRNA expression were examined in golden pompano (Trachinotus ovatus) that fed respectively six diets containing dandelion extracts (DE) at 0, 0.5, 1, 2, 4 and 10 g kg^-1 after 8 weeks feeding. The study indicated that dietary DE significantly improved intestinal antioxidant abilities by increasing SOD, CAT, T-AOC activities and up-regulating intestinal cat, gpx mRNA levels, but by decreasing MDA content and down-regulating intestinal keap1 mRNA levels in golden pompano. Meanwhile, dietary DE improved intestinal morphology, suggesting that enhances intestinal digestion and absorption, by increasing muscle thickness, villus length, villus width and villus number in the foregut and hindgut; as well as villus number, villus width and muscle thickness in the midgut (P < .05). Dietary DE enhanced intestinal barrier function by increasing intestinal zo-1 and occludin mRNA levels, but by decreasing the mRNA levels of claudin-12 and claudin-15. Furthermore, dietary DE improved intestinal immunity via increasing goblet cells numbers and regulating expression of immune-related genes. In conclusion, dietary DE supplementation promoted intestine health by improving intestine morphology, immunity, antioxidant abilities and intestinal barrier in golden pompano.

Effects of dietary hawthorn extract on growth performance, immune responses, growth- and immune-related genes expression of juvenile golden pompano (Trachinotus ovatus) and its susceptibility to Vibrio harveyi infection

The present study was conducted to investigate the effects of dietary hawthorn extract (HTE) supplementation on growth performance, immune responses, hepatic antioxidant abilities, growth- and immune-related and heat shock protein genes expression and resistance to the pathogen Vibrio harveyi in Trachinotus ovatus. A basal diet supplemented with HTE at 0 (Diet 1), 0.50 (Diet 2), 1.00 (Diet 3), 2.00 (Diet 4), 4.00 (Diet 5) and 10.00 (Diet 6) g kg^-1 were fed to golden pompano for 8 weeks. The highest final body weight, weight gain rate, specific growth rate, feed efficiency ratio and protein efficiency rate were observed in fish fed Diet 2 (P < 0.05). Dietary HTE significantly increased plasma complement 3, complement 4 and immunoglobulin M content (P < 0.05). Hepatic antioxidant enzymes (SOD, T-AOC, CAT, GPx, GR) significantly increased (P < 0.05), whereas MDA content decreased first and then increased in fish fed HTE supplement. After challenge with Vibrio harveyi, significant higher post-challenge survival was observed in fish fed Diet 2 and Diet 3 than the control group (P < 0.05). Transcription levels of growth-related genes (IGF-I and IGF-II) were significantly up-regulated in fish fed HTE supplement (P < 0.05), whereas HSP70 and HSP90 mRNA levels were significantly down-regulated (P < 0.05). With respect to immune-related genes, such as tumour necrosis factor-alpha (TNF-α), interleukin-8 (IL-8) and inhibitor protein κBα (IκB-α), upregulation was observed in the liver of fish fed with the diet supplemented with HTE. In contrast, the expression of antioxidant enzyme genes (CAT, GPx, MnSOD and Keap1) and cytokines (IL-10, TGF-β1 and TOR) was downregulated. These results indicated that golden pompano fed a diet supplemented with 0.50 g kg^-1 HTE could significantly promote growth performance and growth-related genes expression, strengthen immunity, and improve hepatic antioxidative abilities and resistance to Vibrio harveyi infection.

Thymosin β4 is involved in the antimicrobial immune response of Golden pompano, Trachinotus ovatus

Thymosin beta belongs to the thymosin family, which consists of a series of highly conserved peptides involved in various biological processes. In teleosts, understanding of the immunological functions of thymosin beta is limited, particularly in vivo, which is essentially unknown. In the current study, we cloned and identified thymosin beta 4 from the teleost fish Golden pompano (Trachinotus ovatus), which we have named TroTβ4. We investigated the expression patterns and functions of TroTβ4 in both in vivo and in vitro assays. TroTβ4 is composed of 44 amino acids and shares high sequence identities with known thymosin β4 species in other teleosts, which contains a highly conserved actin-binding motif (LKKTET). The expression of TroTβ4 was most abundant in immune organs, and was significantly up-regulated in response to infection bacterial with one of a number of bacteria (including Edwardsiella tarda, Vibrio harveyi, and Streptococcus agalactiae). Purified recombinant TroTβ4 (rTroTβ4) inhibited the growth of bacteria, as measured using an automatic growth curve analyzer, indicating that TroTβ4 has antimicrobial functions. When administered in vivo, overexpression of TroTβ4 in T. ovatus, bacterial colonization of tissues was significantly reduced. In contrast, when a DNA vector-based siRNA technology was used to knock down TroTβ4 expression, bacterial dissemination and colonization of tissues increased significantly. Taken together, these results provide the first in vivo evidence to indicate that teleost thymosin beta 4 plays a significant role in innate antibacterial immune responses in addition to in vitro bacteriostatic activity. This provides valuable information regarding the biological functions of teleost thymosin beta.

Occurrence and dietary exposure assessment of PFOS and PFOA in cultured Trachinotus ovatus in China

In this study, investigation was conducted into concentrations of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in Chinese farmed Trachinotus ovatus between 2014 and 2015 using a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) and ultra fast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS) method. The tissue distribution (muscle, skin, liver, kidney and gill) in Trachinotus ovatus was also assessed. The detection frequencies of PFOS and PFOA in fish were 92% and 3%, respectively, and the mean concentrations were 0.392 and 0.015 μg/kg wet weight. The analysis of PFOS distribution in different tissues in Trachinotus ovatus showed the following trend: skin> gill> kidney> liver> flesh. Results revealeded farmed Trachinotus ovatus in China to generally be contaminated with PFOS. Moreover, the average daily intake for Chinese urban residents calculated on the basis of pollution content was 0.268 ng/kg body weight/d (PFOS) and 0.014 ng/kg body weight /d (PFOA), respectively. Both hazard ratio values were less than 1, indicating that exposure levels of PFOS and PFOA through Trachinotus ovatus consumption may not lead to adverse health effects in the Chinese population.

Molecular cloning, structural modeling, and expression analysis of MyD88 and IRAK4 of golden pompano (Trachinotus ovatus)

MyD88 and IRAK4 are important components of TLR signaling pathways. However, information about MyD88 and IRAK4 is vacant in golden pompano (Trachinotus ovatus), a marine teleost with great commercial value. Thus, in this study the full lengths of trMyD88 and trIRAK4 were cloned from golden pompano using RT-PCR and RACE-PCR methods. trMyD88 was 1213 bp in length, encoding a putative protein of 288 amino acids (aa), consisting of a 99 aa of death domain at its N-terminal and a 137 aa of the TIR domain at its C-terminal. trIRAK4 was 1606 bp in length, encoding a putative protein of 469 aa, including an N-terminal death domain and a central kinase domain, connected by a ProST domain. Other domains or aa residues needed for their functions were also identified in trMyD88 and trIRAK4. Physicochemical features and 3-D structures of trMyD88 and trIRAK4 were also analyzed. Quantitative real-time PCR revealed that the 2 genes were ubiquitously expressed in tissues from healthy pompano, especially highly in the spleen and head kidney, indicating their roles in the immune response. Further, trMyD88 and trIRAK4 were up-regulated at 12 h after the Vibrio alginilyticus and polyI:C challenge and continued to 48 h post challenge. Our results demonstrated that MyD88 and IRAK4 played important roles in the golden pompano innate immune system, providing the basis for further study of the signaling pathways that these 2 genes are involved in.

Identification, polymorphism and expression of MHC class Iα in golden pompano, Trachinotus ovatus

The classical major histocompatibility complex class I (MHC I) plays a vital role in the immune system. In this study, we cloned and identified golden pompano (Trachinotus ovatus) MHC Iα (Trov-MHC Iα), which encodes 351 amino acid residues including a leader peptide, α1, α2, α3 domain, a transmembrane region and a cytoplasmic domain. Twenty six different sequences, which encoded various numbers of amino acid residues ranging from 348 to 354, were obtained from 12 individuals. Highly genetic polymorphism was found in the Trov-MHC Iα, especially in the α1 and α2 domains. Meanwhile, in the α1 and α2 domains, 21 positive selected positions were revealed by site models, indicating the diversity of Trov-MHC Iα may be mainly generated by positive selection. Moreover, quantitative real-time reverse transcription PCR and western blotting analyses demonstrated that Trov-MHC Iα was ubiquitously expressed in the nine tested tissues and more highly expressed in intestine, head kidney, gill, and spleen. In the head kidney and spleen, Trov-MHC Iα was significantly upregulated under LPS or poly I:C stimulation. The results of this study provide valuable insight into molecular polymorphism, evolutionary mechanism, expression and function of MHC Iα in the immune system of golden pompano.

Effects of dietary dandelion extracts on growth performance, body composition, plasma biochemical parameters, immune responses and disease resistance of juvenile golden pompano Trachinotus ovatus

The present study was conducted to investigate the effects of dietary dandelion extracts (DE) supplementation on growth performance, feed utilization, body composition, plasma biochemical indices, immune responses, hepatic antioxidant abilities, and resistance to the pathogen Vibrio harveyi in Trachinotus ovatus. A basal diet supplemented with DE at 0, 0.50, 1.00, 2.00, 4.00 and 10.00 g kg^-1 were fed to golden pompano for 8 weeks. The study indicated that dietary supplementation with DE could significantly improve final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), feed efficiency ratio (FER), feed intake (FI), protein efficiency ratio (PER) and protein deposit rate (PDR) (P < 0.05). The highest FBW, WGR, SGR, FI and PDR were observed in fish fed 1.00 g kg^-1 dietary DE (P < 0.05). The highest FER and PER were recorded at 0.50 g kg^-1 dietary DE (P < 0.05). Condition factor, viscerosomatic index, hepatosomatic index and survival were not significantly different among all groups. Fish fed 1.00 g kg^-1 dietary DE showed significant increase in plasma total protein, complement 4 content and alkaline phosphatase, lysozyme, glutathione reductase (GSR) activity, but significant decrease in triglyceride, low density lipoprotein cholesterol, malondialdehyde (MDA) content and aspartate aminotransferase activities compared to the control group (P < 0.05). Hepatic antioxidant enzymes (SOD, T-AOC, CAT, GSH-Px, GSR) significantly increased whereas MDA content significantly decreased in fish fed 1.00 g kg^-1 DE supplement (P < 0.05). After challenge with Vibrio harveyi, significant higher post-challenge survival was observed in fish fed DE supplement (P < 0.05). These results indicated that golden pompano fed a diet supplemented with DE (especially at 1.00 g kg^-1 of fed supplement) could significantly promote its growth performance, feed utilization, body protein deposit, immune ability, hepatic and plasma antioxidative enzyme activities and improve its resistance to infection by Vibrio harveyi.

Molecular characterization and expression of interleukin-10 and interleukin-22 in golden pompano (Trachinotus ovatus) in response to Streptococcus agalactiae stimulus

In the present study, members of the interleukin (IL)-10 family of cytokines, including IL-10 (TOIL-10) and IL-22 (TOIL-22) of golden pompano (Trachinotus ovatus), were cloned for the first time, and their expression patterns and 3D structures analyzed. The full-length cDNA sequences of TOIL-10 and TOIL-22 contained open reading frames of 564 and 567 bp, respectively. TOIL-10 and TOIL-22 shared higher homology (78%-89%) with the corresponding genes from various fish relative to other species (25%-34%) and contained the IL-10 family signature and four cysteine residues that are well conserved in other vertebrate IL-10 members. Phylogenetic tree analysis of our sequences alongside other IL-10 family proteins revealed that TOIL-10 and TOIL-22 cluster together with other teleost IL-10 and IL-22 molecules. Expression of TOIL-10 and TOIL-22 genes was ubiquitous in all tissues examined. The TOIL-10 gene was also highly expressed in skin, heart, gill, spleen, kidney, brain and liver, and lower levels were detected in intestine and muscle. High expression of the TOIL-22 gene was observed in gill, intestine, kidney, spleen, with the lowest levels in liver. TOIL-10 and TOIL-22 were rapidly activated after SAΔphoB immunization and significantly increased to peak levels at 12 h and 4 d in golden pompano kidney and spleen respectively following challenge. Expression in the brain reached peak levels at 4 d and 3 d respectively after post-immunization. Our results collectively indicate that TOIL-10 and TOIL-22 participate in the host immune response to bacterial infection. Moreover, TOIL-22 plays a potentially important role in mucosal immunity.

Establishment and characterization of a cell line from the head kidney of golden pompano Trachinotus ovatus and its application in toxicology and virus susceptibility

A cell line derived from the head kidney of golden pompano Trachinotus ovatus (TOHK) was established and characterized in this study. The TOHK cells grew most rapidly at 28° C and the optimum foetal bovine serum concentration in L-15 medium was 10%. The TOHK cells have a diploid chromosome number of 2N = 54. The transfection efficiency of TOHK cells was 7·5% at the 15th passage and 72% at the 40th passage. The transfection efficiency in TOHK cells was high, so these cells are suitable for foreign gene expression. The cytotoxic effects of heavy metals and extracellular products from Vibrio anguillarum and Vibrio alginolyticus were demonstrated in TOHK cells, so this TOHK cell line could also be applied in environmental monitoring of heavy metals and pathogenic bacteria. TOHK cell line showed high virus susceptibility, such as grouper nervous necrosis virus (GNNV) and Singapore grouper iridovirus (SGIV). Then, TOHK cell line could be used for the study of viral pathogenesis and the development of antiviral strategies.

Molecular cloning and expression analysis of toll-like receptor genes (TLR7, TLR8 and TLR9) of golden pompano (Trachinotus ovatus)

Toll like receptor (TLR) 7, 8 and 9 are intracellular TLRs which play important roles in host immune defense against bacterial or virus pathogens. In this study, TLR7, 8 and 9 were identified from golden pompano (Trachinotus ovatus), a marine teleost with great economic values. Sequence analysis revealed that the three TLRs contained several conserved characteristic features, including signal peptides, 25 leucine-rich repeat (LRR) motifs, a transmembrane domain and a TIR motif. These three TLRs shared high sequence identity and similarity with their counterparts from other teleosts. The phylogenetic tree analysis showed the three TLRs were clustered well with their piscine counterparts, confirming the correctness of their nomenclatures and closed relationships during evolution. Quantitative real-time PCR revealed that the three TLRs were ubiquitously expressed in all the tested tissues from normal pompano, with high expression in spleen and head kidney, indicating their role in immune reaction. Further, pompano TLR7 and TLR8 was up-regulated in spleen and head kidney from 12 h to 48 h following polyI:C challenge, but remained no changes to Vibrio alginilyticus infection. In contrast, pompano TLR9 could be induced by V. alginilyticus infection but remained apathetic to polyI:C challenge. These results indicated that pompano TLR7, 8 and 9 might have distinct roles in response to bacterial or virus pathogens. Our results provided the basis for further study on ligand specificity and signaling pathways of fish TLRs which are required for elucidating the immune functions of fish TLRs.

Establishment and characterization of a mid-kidney cell line derived from golden pompano Trachinotus ovatus, a new cell model for virus pathogenesis and toxicology studies

Golden pompano Trachinotus ovatus, a popularly cultured and commercially important marine fish worldwide, has been recognized as a promising candidate for mariculture. However, outbreaks of infectious bacterial or viral diseases and environmental deterioration have led to great economic losses in T. ovatus aquaculture recently. In our research, we established a new mid-kidney cell line, designated as TOK, from golden pompano, T. ovatus. The optimized growth temperature and working concentration of fetal bovine serum (FBS) were 28°C and 10-20%, respectively. Foreign genes could express well in TOK cells. The modal number of TOK cells was 54. The TOK cells were susceptive to Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV), and the virus could propagate in cells. Propagation was verified by qRT-PCR, and virions were observed under electron microscopy. Cytotoxicity analysis revealed that TOK cells were sensitive to different concentrations of extracellular products (ECPs) from Vibrio alginolyticus and V. anguillarum. Moreover, heavy metals (Cd, Cu, and Hg) also showed dose-dependent cytotoxicity to the TOK cell line. We established a mid-kidney cell line from T. ovatus which could be applied to cytotoxicity assays of heavy metals. The newly established TOK cell line possesses great application potential in genetic manipulation, virus-host interaction studies, and toxicity assays of bacterial extracellular products and heavy metals.

Dietary β-glucan improved growth performance, Vibrio counts, haematological parameters and stress resistance of pompano fish, Trachinotus ovatus Linnaeus, 1758

This study evaluated effects of graded levels of dietary β-glucan (0, 0.5, 1, 2 and 4 g kg(-1)) on growth performance, haematological parameters, intestinal Vibrio counts, dose requirement and salinity stress resistance in pompano fish Trachinotus ovatus (6.45 g ± 0.06 (SEM)). After 8-weeks of diet feeding, growth was significantly higher in fish fed diets with 0.10% β-glucan compared to fish fed control diet (no β-glucan). Survival increased significantly in fish fed 0.05 and 0.10% β-glucan compared to control diet. There were significant increases in red blood cells (in 0.20% β-glucan diet), in total leukocytes (in 0.05-0.20% β-glucan diet), in both lymphocyte and monocyte count in fish fed 0.10%-0.40% β-glucan diet. However, dietary β-glucan did not affect neutrophil, eosinophil and basophil counts. Intestinal Vibrio counts were reduced in fish fed any level of β-glucan compared to control. In addition, dietary β-glucan levels highly correlated with growth, survival, intestinal Vibrio counts and haematological index. Optimal β-glucan levels for maximal growth of fish were predicted to be 0.122% at day 21 (R(2) = 98.53%), 0.120% at day 28 (R(2) = 78.55%), 0.115% at day 42 (R(2) = 62.21%) and 0.090% at day 56 (R(2) = 75.18%), showing a decreasing β-glucan requirement with increasing fish size. Furthermore, optimal β-glucan levels for maximal haematological parameters based on lymphocyte count, was estimated to be 0.120% (R(2) = 98.53%) at day 56. Also, fish fed 0.05%-0.20% β-glucan showed better resistance against salinity stress. In conclusion, β-glucan supplementation is effective for improving growth, intestinal Vibrio counts and boosted stress resistance of the pompano fish, T. ovatus.

Effects of dietary soybean isoflavones on non-specific immune responses and hepatic antioxidant abilities and mRNA expression of two heat shock proteins (HSPs) in juvenile golden pompano Trachinotus ovatus under pH stress

This study determined the effect of dietary soybean isoflavones on non-specific immunity and on mRNA expression of two HSPs in juvenile golden pompano Trachinotus ovatus under pH stress. Six diets were formulated to contain 0, 10, 20, 40, 60 and 80 mg/kg of soybean isoflavones. Each diet was fed to triplicate groups of fish in cylindrical tanks. After 56 days of feeding, 15 fish per tank were exposed to pH stress (pH ≈ 9.2) for 24 h. Serum total protein (TP), respiratory burst activity (RBA), alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (AKP), lysozyme (LYZ), complement 3 (C3), complement 4 (C4), cortisol, hepatic total antioxidant capacity (T-AOC), superoxide dismutase (SOD), malondialdehyde (MDA), catalase (CAT) and the relative mRNA expression of heat shock protein 70 (HSP70) and 90 (HSP90) were investigated. The results showed that after pH stress, serum TP, RBA, LYZ, C4, hepatic T-AOC and CAT levels were significantly reduced (P < 0.05) while serum ALT, hepatic MDA and HSP70 and HSP90 mRNA expression levels were significantly increased (P < 0.05). On the other hand, supplementation with soybean isoflavones significantly reduced levels of serum ALT (20, 40, 60 mg/kg soybean isoflavones groups) and hepatic MDA (40, 60 and 80 mg/kg soybean isoflavones groups). Supplemented groups had increased serum TP content (40 mg/kg soybean isoflavones groups), RBA (20 and 40 mg/kg soybean isoflavones groups), LYZ (40 and 60 mg/kg soybean isoflavones groups), C3(20, 40, 60 and 80 mg/kg soybean isoflavones groups), hepatic SOD activity (40, 60 and 80 mg/kg soybean isoflavones groups) as well as increased relative mRNA expression of hepatic HSP70 (40, 60 and 80 mg/kg soybean isoflavones groups) and HSP90 (40 and 60 mg/kg soybean isoflavones groups) (P < 0.05). These results indicate that ingestion of a basal diet supplemented with 40-60 mg/kg soybean isoflavones could enhance resistance against pH stress in T. Ovatus to some degree.

Thioredoxin of golden pompano involved in the immune response to Photobacterium damselae

Thioredoxin (TRX) is one of the key systems responsible for keeping the intracellular environment in a highly reduced state. In this study, a full-length TRX cDNA sequence (ToTRX) from golden pompano Trachinotus ovatus was identified after pyrosequencing of golden pompano cDNA library. ToTRX cDNA is comprised of 786 bp, and contained a 324 bp open reading frame (ORF) encoding a 107 amino acid polypeptide, a 5' untranslated region (UTR) of 116 bp, and a long 3'- UTR of 346 bp. Multiple sequence alignment revealed that ToTRX contained the highly conserved redox active disulphide/dithiol site (CGPC) of the thioredoxin active family, and phylogenetic tree showed that ToTRX had a closer evolution relationship with TRX from Oplegnathus fasciatus and Anoplopoma fimbria. ToTRX mRNA is ubiquitously expressed in all detected tissues with the higher expression levels in the stomach, gill and fin tissues. The expression of ToTRX mRNA was significantly up-regulated in liver, kidney, intestine and spleen of golden pompano injected with Photobacterium damselae. The recombinant ToTRX protein (rToTRX) was expressed in Escherichia coli BL21 (DE3), and then purified and refolded. The insulin disulfides assay was performed to investigate the enzymatic oxidoreductase activity of rToTRX, and the results demonstrated that rToTRX exhibited a high reducing activity in presence of DTT, while no activity was observed in the regroup without DTT and blank control group. Over all, the study provided the useful information to help further understand the functional mechanism of TRX in marine fish immunity.

Molecular characterization and functional analysis of a peroxiredoxin 1 cDNA from golden pompano (Trachinotus ovatus)

Peroxiredoxin 1 (Prx 1) is an important antioxidant protein that can protect organisms against the toxicity of reactive oxygen species. In this study, a full-length Prx 1 cDNA sequence (ToPrx 1) was identified from golden pompano (Trachinotus ovatus). The ToPrx 1 cDNA was 1049 base pairs (bp) long and contained a 5'-untranslated region (UTR) of 127 nucleotides, a 3'-UTR of 328 nucleotides, and a 594 bp open reading frame (ORF) encoding a 197 amino acid polypeptide. The ToPrx 1 protein showed strong homology (79-91%) with Prx 1 proteins from other species and contained the conserved Prx domain and the signature of the peroxidase catalytic center. Phylogenetic analysis revealed that ToPrx 1 was in the fish Prx 1 subgroup, which suggests that ToPrx 1 could belong to the 2-Cys Prx subgroup. ToPrx 1 mRNA was ubiquitously detected in all tested tissues, and its expression was comparatively high in the fin, spleen, kidney, intestine, eye, gill, and blood. The expression levels of ToPrx 1 mRNA were significantly up-regulated in liver, spleen, kidney, and intestine of golden pompano injected with Photobacterium damselae. The recombinant ToPrx 1 protein (rToPrx 1) was expressed and purified through affinity chromatography and refolded successfully using ion-exchange chromatography. The antioxidant activity assay of rToPrx 1 showed that it could reduce insulin in the presence of dithiothreitol, which suggests that the antioxidant function of rToPrx 1 is thiol dependent. This study provides useful information to help further understand the functional mechanism of Prx 1 in marine fish immunity.

The effects of dietary soybean isoflavones on growth, innate immune responses, hepatic antioxidant abilities and disease resistance of juvenile golden pompano Trachinotus ovatus

The present study was conducted to investigate the effects of dietary soybean isoflavones (SI) supplementation on growth performance, innate immune responses, hepatic antioxidant abilities, heat shock protein 70 (HSP70) gene expression and resistance to the pathogen Vibrio harveyi in Trachinotus ovatus. A basal diet was supplemented with SI at 0, 10, 20, 40, 60, 80 mg kg(-1) feed for 8 weeks. Significantly maximum weight gain (WG) and specific growth rate (SGR) were observed in treatment with 40 mg kg(-1) SI supplement (P < 0.05). Feed conversion ratio (FCR), feeding rate (FR) and survival rate were not significantly different among treatments. Fish fed a diet with 40 mg kg(-1) SI showed significant increase in plasma total protein content, complement 3 content, lysozyme activity as well as respiratory burst activity, but decrease in alanine aminotransferase and aspartate aminotransferase activities (P < 0.05). Increased plasma alkaline phosphatase activity, hepatic total antioxidative capacity, catalase activity and superoxide dismutase activity were also noticed in fish fed SI at 40 or 60 mg kg(-1) (P < 0.05). On the contrary, the lowest hepatic malondialdehyde (MDA) content was observed in fish fed SI at 40 mg kg(-1) (P < 0.05). Compared with the control, the relative level of HSP70 mRNA in fish fed SI at 40-80 mg kg(-1) were significantly increased, respectively (P < 0.05). After challenge with V. harveyi, significant higher post-challenge survival was observed in fish fed diets with 40-80 mg kg(-1) SI supplement than that in control group (P < 0.05). These results indicated that dietary intake containing SI could enhance the immune ability of fish and improve its resistance to infection by V. harveyi. Especially supplementation with 40 mg kg(-1) SI to the fish for 8 weeks showed remarkable improvement in the growth, non-specific immune responses, hepatic antioxidant abilities and HSP70 gene expression.

Effect of dietary carbohydrate on non-specific immune response, hepatic antioxidative abilities and disease resistance of juvenile golden pompano (Trachinotus ovatus)

The present study was conducted to investigate the effects of dietary carbohydrate (CHO) levels on non-specific immune responses, hepatic antioxidative status and disease resistance of juvenile golden pompano. Fish were fed six isonitrogenous and isoenergetic diets containing various CHO levels for 8 weeks. After the feeding trial, fish were challenged by Vibrio harveyi and survival rate was recorded for the next 12 days. Plasma total protein and albumin content, respiratory burst activity, alkaline phosphatase, slightly increased with dietary starch level from 0% to 16.8%, but significantly decreased at dietary starch levels of 16.8%-28%. Plasma lysozyme, complement 3 and complement 4 levels increased with increasing dietary carbohydrate up to 11.2% and then declined (P < 0.05). Contrary to glutamic-oxalacetic transaminase and triiodothyronine, plasma cortisol content increased with increasing dietary carbohydrate up to 22.4%, and then levelled off. The hepatic total antioxidative capacity, reduced glutathione and catalase levels reached the peak at the fish fed diet with 16.8% carbohydrate (P < 0.05). This also held true for hepatic superoxide dismutase activities, whereas the hepatic malondialdehyde content of fish fed dietary starch level of 16.8% was significantly lower than that of fish fed no CHO diet, but showed little difference (P > 0.05) with those of the other treatments. After challenge, fish fed 11.2% and 16.8% dietary CHO showed higher survival rate than that of fish in 0% CHO group (P < 0.05). However, survival rate showed little difference among 0%, 5.6%, 22.4% and 28% CHO groups (P > 0.05). The results of this study suggest that ingestion of 11.2-16.8% dietary CHO can enhance the non-specific immune responses, increase the hepatic antioxidant abilities, and improve resistance to V. harveyi infection of juvenile golden pompano.

Complete mitochondrial genome sequence of golden pompano Trachinotus ovatus

The complete mitochondrial genome of Trachinotus ovatus was determined by the polymerase chain reaction (PCR). The mitogenome is 16,564 bp long and has the typical vertebrate mitochondrial gene arrangement, including 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and one control region. The overall base composition of mitogenome is estimated to be 29.0% for A, 28.9% for C, 26.2% for T, 15.9% for G, respectively, with a high A + T content (55.2%). With the exception of ND6 and eight tRNA genes, all other mitochondrial genes are encoded on the heavy strand. The control region contains a dinucleotide repeat motif, (AT)5. This mitogenome sequence would play an important role in population genetics and the molecular taxonomy of T. ovatus.

Dietary supplementation of Bacillus subtilis and fructooligosaccharide enhance the growth, non-specific immunity of juvenile ovate pompano, Trachinotus ovatus and its disease resistance against Vibrio vulnificus

A feeding trial was conducted to investigate the effects of dietary administration of probiotic Bacillus subtilis and prebiotic fructooligosaccharide (FOS) on growth performance, immune responses and disease resistance of juvenile ovate pompano, Trachinotus ovatus. One thousand six hundred and twenty individuals (initial body weight: 10.32 ± 0.46 g, mean ± S.E) were fed nine practical diets according to a 3 × 3 factorial design: the basal diet as the control diet supplemented with three levels of B. subtilis (0, 1.05 × 10(7) or 5.62 × 10(7) CFU g(-1) diet), crossed with 0, 0.2% or 0.4% FOS. After an 8-week feeding experimental period, six fish per cage were sampled for immunity determination. Then 18 fish of each cage left were challenged by Vibrio vulnificus. The results showed that fish fed with 5.62 × 10(7) CFU B. subtilis g(-1) in combination with 0.2% FOS produced the highest specific growth rate, and were significantly higher than the groups fed with 0 and 0.2% FOS without B. subtilis supplementation (P < 0.05). Feed efficiency ratio significantly increased with the increasing doses of dietary FOS without B. subtilis added (P < 0.05). The immune assay showed that fish fed with the control diet produced the lowest respiratory burst activity and was significantly different from the groups fed the diets containing 0.2% FOS at each B. subtilis level and containing 0.4% FOS single (P < 0.05). Phagocytic activity was significantly decreased with the increasing doses of dietary B. subtilis at 0.4% FOS level (P < 0.05). Alternative complement pathway activity of the fish fed with 0.2% FOS single was significantly lower than those fed with 5.62 × 10(7) CFU B. subtilis g(-1) diet supplemented at each FOS level (P < 0.05). Fish fed with the control diet had the lowest lysozyme activity, and were significantly different from those fed with 0.2 or 0.4% FOS at 1.05 and 5.62 × 10(7) CFU B. subtilis g(-1) diet level. Moreover, fish fed with diets supplemented with 0.2% and 0.4% FOS at each B. subtilis level had notably lower cumulative mortality after 10 days following V. vulnificus infection (P < 0.05). Under the experimental conditions, dietary B. subtilis and FOS had a significant interaction on enhancing the immune responses and disease resistance of juvenile ovate pompano (P < 0.05).