Macrophage migration inhibitory factor (MIF) of golden pompano (Trachinotus ovatus) is involved in the antibacterial immune response

Identification and functional analysis of lysophosphatidic acid phosphatase type 6 (ACP6) gene in golden pompano (Trachinotusovatus)

Golden pompano (Trachinotus ovatus), a marine farmed fish, is economically valuable in China. Lysophosphatidic acid phosphatase type 6 (ACP6) is a type of histidine acid phosphatase and plays an important role in regulating host inflammatory responses and anti-cancer effects in mammals. However, its function in teleost remains unknown. The present study aimed to investigate ACP6 function in golden pompano. ACP6 from golden pompano was identified, cloned, and named TroACP6. The open reading frame of TroACP6 was 1275 bp in length, encoding 424 amino acids. The TroACP6 protein shared high sequence identity (43.32%-90.57 %) with the ACP6 of other species. It contained a histidine phosphatase domain with the active site motif "RHGART" and the catalytic dipeptide HD (histidine and aspartate). Meanwhile, TroACP6 mRNA was widely distributed in the various tissues of healthy golden pompano, with the maximum expression in the head kidney. The function of TroACP6 was analyzed both in vitro and in vivo, and the results revealed that the purified recombinant TroACP6 protein exhibited optimum phosphatase activity at pH 6.0 and 50 °C in vitro. Meanwhile, upon Edwardsiella tarda challenge, TroACP6 expression in tissues increased significantly in vivo. In addition, TroACP6 overexpression enhanced the respiratory burst activity and superoxide dismutase activity of head kidney macrophages in vivo. Furthermore, the overexpression and knockdown of TroACP6 in vivo had a significant effect on bacterial infection. In summary, the study findings indicate that TroACP6 in golden pompano is involved in host defense against bacterial infection.

Larimichthys crocea (large yellow croaker): A bibliometric study

Larimichthys crocea is an important economic fish of East Asia, and numerous studies have been conducted on its breeding, aquaculture, preservation and processing; however, there is no systematic review of the literature on the research of Larimichthys crocea. Derwent Data Analyzer (DDA) was used to analyze 1192 Larimichthys crocea research papers indexed by SCI-E, CSCD and KCI from 2001 to 2023. The number of research publications on Larimichthys crocea has rapidly increased, and institutions and scholars from China, the United States, South Korea, Japan, and Norway have conducted the majority of Larimichthys crocea research. The immune response, Pseudomonas plecoglossicida, gene expression, lipid immune response, transcriptomics and other areas have attracted the most attention. To increase the immunity and disease resistance of Larimichthys crocea and improve its survival, growth, storage and transport, researchers have carried out a large amount of research, which has promoted not only the culture of Larimichthys crocea but also the restoration of wild Larimichthys crocea and the rehabilitation of the ecological environment.

Bacterial infection-biased abundance of proteins in the skin mucus of obscure puffer (Takifugu Obscurus)

The skin mucus of fish is equipped with immunological and antimicrobial peptides that confer protection against invading pathogens. The skin mucus has been studied in fish however information regarding its immunological roles in bacterial infection is rare. This study highlighted the proteins and peptides in the skin mucus of Obscure puffer Takifugu obscurus that quantitatively altered against Aeromonas hydrophila infection. We infected the fish through bath immersion, intraperitonially, and treated with PBS (control) then compared the level of proteins in the skin mucus among the groups using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. The Tandem Mass Tag (TMT) based quantification showed that 4896 proteins were Deferentially Quantified Proteins (DQPs), based on 19,751 unique peptides. Of which 170 were depleted (decreased in abundance) and 69 were abundant in comparison of Bath Treated (BT) vs Control (C) groups. Similarly, 76 DQPs were depleted and 70 were abundant in comparison of Treated (T) vs BT groups. Further, 126 DQPs were depleted, and 34 were abundant in comparison to T vs C groups. The DQPs we report were mostly immunological and were involved in unique biological functions and pathways. The interesting protein we report, where some of the proteins are for the first time in fish, shows the protein-rich structure of the mucus of fish, which may act as a biomarker to be targeted for bacterial disease therapy in fish and ultimately hint to the way of making resistance in fish against bacterial pathogens.

Whole-Genome Sequencing Analyses Reveal the Whip-like Tail Formation, Innate Immune Evolution, and DNA Repair Mechanisms of Eupleurogrammus muticus

Smallhead hairtail (Eupleurogrammus muticus) is an important marine economic fish distributed along the northern Indian Ocean and the northwest Pacific coast; however, little is known about the mechanism of its genetic evolution. This study generated the first genome assembly of E. muticus at the chromosomal level using a combination of PacBio SMRT, Illumina Nova-Seq, and Hi-C technologies. The final assembled genome size was 709.27 Mb, with a contig N50 of 25.07 Mb, GC content of 40.81%, heterozygosity rate of 1.18%, and repetitive sequence rate of 35.43%. E. muticus genome contained 21,949 protein-coding genes (97.92% of the genes were functionally annotated) and 24 chromosomes. There were 143 expansion gene families, 708 contraction gene families, and 4888 positively selected genes in the genome. Based on the comparative genomic analyses, we screened several candidate genes and pathways related to whip-like tail formation, innate immunity, and DNA repair in E. muticus. These findings preliminarily reveal some molecular evolutionary mechanisms of E. muticus at the genomic level and provide important reference genomic data for the genetic studies of other trichiurids.

Antibacterial Activity and Mechanisms of TroHepc2-22, a Derived Peptide of Hepcidin2 from Golden Pompano (Trachinotus ovatus)

Hepcidin, a cysteine-rich antimicrobial peptide, has a highly conserved gene structure in teleosts, and it plays an essential role in host immune response against various pathogenic bacteria. Nonetheless, few studies on the antibacterial mechanism of hepcidin in golden pompano (Trachinotus ovatus) have been reported. In this study, we synthesized a derived peptide, TroHepc2-22, from the mature peptide of T. ovatus hepcidin2. Our results showed that TroHepc2-22 has superior antibacterial abilities against both Gram-negative (Vibrio harveyi and Edwardsiella piscicida) and Gram-positive (Staphylococcus aureus and Streptococcus agalactiae) bacteria. Based on the results of a bacterial membrane depolarization assay and propidium iodide (PI) staining assay in vitro, TroHepc2-22 displayed antimicrobial activity by inducing the bacterial membrane depolarization and changing the bacterial membrane permeability. Scanning electron microscopy (SEM) visualization illustrated that TroHepc2-22 brought about membrane rupturing and the leakage of the cytoplasm for the bacteria. In addition, TroHepc2-22 was verified to have hydrolytic activity on bacterial genomic DNA in view of the results of the gel retardation assay. In terms of the in vivo assay, the bacterial loads of V. harveyi in the tested immune tissues (liver, spleen, and head kidney) were significantly reduced in T. ovatus, revealing that TroHepc2-22 significantly enhanced the resistance against V. harveyi infection. Furthermore, the expressions of immune-related genes, including tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin 1-β (IL-1β), IL-6, Toll-like receptor 1 (TLR1), and myeloid differentiation factor 88 (MyD88) were significantly increased, indicating that TroHepc2-22 might regulate inflammatory cytokines and activate immune-related signaling pathways. To summarize, TroHepc2-22 possesses appreciable antimicrobial activity and plays a vital role in resisting bacterial infection. The observation of our present study unveils the excellent application prospect of hepcidin as a substitute for antibiotics to resist pathogenic microorganisms in teleosts.

Effects of cysteine addition to low-fishmeal diets on the growth, anti-oxidative stress, intestine immunity, and Streptococcus agalactiae resistance in juvenile golden pompano (Trachinotus ovatus)

As the precursor of taurine, cysteine serves physiological functions, such as anti-oxidative stress and immune improvement. Investigation of cysteine and its derivatives has made positive progress in avian and mammalian species, yet the study and application of cysteine in aquatic animals are relatively rare. Therefore, we evaluated the effects of supplementing a low-fishmeal diet with various levels of cysteine on the growth, antioxidant capacity, intestine immunity, and resistance against Streptococcus agalactiae of the juvenile golden pompano (Trachinotus ovatus). According to our study, exogenous supplementation with 0.6-1.2% cysteine greatly increased the final body weight (FBW) and specific growth rate (SGR) of golden pompano compared to the control group. Under the present conditions, the optimum dietary cysteine supplementation level for golden pompano was 0.91% based on the polynomial regression analysis of SGR. Meanwhile, we found that the Nrf2/Keap1/HO-1 signaling pathway was notably upregulated with the increase of exogenous cysteine, which increased antioxidant enzyme activity in serum and gene expression in the intestine and reduced the level of reactive oxygen species (ROS) in the serum of golden pompano. In addition, morphological analysis of the midgut demonstrated that exogenous cysteine improved muscle thickness and villi length, which suggested that the physical barrier of the intestine was greatly strengthened by cysteine. Moreover, cysteine increased the diversity and relative abundance of the intestinal flora of golden pompano. Cysteine suppressed intestinal NF-κB/IKK/IκB signaling and pro-inflammatory cytokine mRNA levels. Conversely, intestinal anti-inflammatory cytokine gene expression and serum immune parameters were upregulated with the supplementary volume of cysteine and improved intestine immunity. Further, exogenous cysteine supplementation greatly reduced the mortality rate of golden pompano challenged with S. agalactiae. In general, our findings provide more valuable information and new insights into the rational use of cysteine in the culture of healthy aquatic animals.

Effects of exogenous taurine supplementation on the growth, antioxidant capacity, intestine immunity, and resistance against Streptococcus agalactiae in juvenile golden pompano (Trachinotus ovatus) fed with a low-fishmeal diet

Taurine has various biological functions in fish, playing an essential role in growth, resistance to oxidative stress, and intestine immunity. Here, we evaluated the effects of exogenous taurine added to low-fishmeal diets on the growth, anti-oxidative stress, intestine immunity, and Streptococcus agalactiae resistance in juvenile golden pompano (Trachinotus ovatus). Our study showed that exogenous taurine supplementation of 1.2% (T3 group) greatly enhanced the weight gain rate and specific growth rate (SGR) of juvenile golden pompano, significantly upregulating growth-related factor expression in the brain and liver, as well as the levels of growth-related parameters in the serum. Polynomial regression analysis using SGR estimated the optimal dietary taurine level for golden pompano at 1.18%. Moderate exogenous taurine also increased the muscular thickness and villus length within the intestine, maintained intestinal physical barrier stability, activated the Nrf2/Keap-1/HO-1 signaling pathway, increased intestinal antioxidant enzyme gene expression and antioxidant enzyme activity in the serum, and upregulated immunoglobulin and complement levels in parallel with declining reactive oxygen species (ROS) levels in the serum. Antioxidant factor expression was also upregulated in the intestine. Furthermore, supplementation suppressed NF-κB signaling and intestinal pro-inflammatory cytokine gene expression, increased anti-inflammatory cytokine gene expression, and improved intestine immunity. Finally, taurine supplementation improved the survival rate of golden pompano challenged with S. agalactiae. Overall, our findings provide additional information and support for the rational use of taurine in healthy aquatic animal farming.