Identification and functional characterization of annexin A2 in half-smooth tongue sole (Cynoglossus semilaevis).

Annexin A2 (AnxA2), belonging to the annexin family, plays a crucial role in immune responses. In this study, the cDNA of the AnxA2 gene was identified in half-smooth tongue sole, Cynoglossus semilaevis. The transcript of AnxA2 gene in C. semilaevis (CsAnxA2) showed broad tissue distribution, with the highest expression level observed in the gut. CsAnxA2 expression was significantly up-regulated in the intestine, spleen, and kidney tissues following exposure to Shewanella algae. Immunohistochemical staining revealed that CsAnxA2 was predominantly expressed in epithelial cells and significantly elevated after S. algae challenge. Subcellular localization showed that CsAnxA2 was primarily localized in the cytoplasmic compartment. Moreover, proinflammatory cytokines (IL-6, IL-8 and IL-1ß) exhibited significant upregulation after CsAnxA2 was overexpressed in vivo. One hundred and fifty-eight CsAnxA2-interacting proteins were captured in the intestinal tissue, showing the top two normalized abundance observed for actin beta (ACTB) and protein S100-A10 (p11). Fifty-four high abundance CsAnxA2-interacting proteins (HIPs) were primary enriched in ten pathways, with the top three significantly enriched pathways being Salmonella infection, glycolysis/gluconeogenesis, and peroxisome proliferator-activated receptor (PPAR) signaling pathway. These results provide valuable information for further investigation into the functional mechanism of AnxA2 in C. semilaevis.

Genome-wide identification, evolution of DNA methyltransferases and their expression under salinity stress in Larimichthys crocea.

DNA methyltransferases (Dnmts) are responsible for DNA methylation which influences patterns of gene expression and plays a crucial role in response to environmental changes. In this study, 7 LcDnmt genes were identified in the genome of large yellow croaker (Larimichthys crocea). The comprehensive analysis was conducted on gene structure, protein and location site of LcDnmts. LcDnmt proteins belonged to three groups (Dnmt1, Dnmt2, and Dnmt3) according to their conserved domains and phylogenetic analysis. Although Dnmt3 can be further divided into three sub groups (Dnmt3a, Dnmt3b, and Dnmt3l), there is no Dnmnt3l member in the large yellow croaker. Phylogenetic analysis revealed that the Dnmt family was highly conserved in teleosts. Expression patterns derived from the RNA-seq, qRT-PCR and Western blot analysis revealed that 2 LcDnmt genes (LcDnmt1 and LcDnmt3a2) significantly regulated under salinity stress in the liver, which was found to be dominantly expressed in the intestine and brain, respectively. These two genes may play an important role in the salinity stress of large yellow croaker and represent candidates for future functional analysis. Our results revealed the conservation of Dnmts during evolution and indicated a potential role of Dnmts in epigenetic regulation of response to salinity stress.

In-depth discovery and taste presentation mechanism studies on umami peptides derived from fermented sea bass based on peptidomics and machine learning.

Umami peptides originating from fermented sea bass impart a distinctive flavor to food. Nevertheless, large-scale and rapid screening for umami peptides using conventional techniques is challenging because of problems such as prolonged duration and complicated operation. Therefore, we aimed to screen fermented sea bass using peptidomics and machine learning approaches. The taste presentation mechanism of umami peptides was assessed by molecular docking of T1R1/T1R3. Seventy umami peptides identified in fermented sea bass predominantly originated from 28 precursor proteins, including troponin, myosin, motor protein, and creatine kinase. Six umami peptides with the lowest energies formed stable complexes by binding to T1R3. SER170, SER147, GLN389, and HIS145 are critical binding sites for T1R1/T1R3. Four dominant interacting surface forces were identified: aromatic interactions, hydrogen bonding, hydrophilic bonds, and solvent-accessible surfaces. Our study unveils a method to screen umami peptides efficiently, providing a basis for further exploration of their flavor in fermented sea bass.

Identification of the C1qDC gene family in grass carp (Ctenopharyngodon idellus) and the response of C1qA, C1qB, and C1qC to GCRV infection in vivo and in vitro.

Proteins from the C1q domain-containing (C1qDC) family recognize self-, non-self-, and altered-self ligands and serves as an initiator molecule for the classical complement pathway as well as recognizing immune complexes. In this study, C1qDC gene family members were identified and analyzed in grass carp (Ctenopharyngodon idellus). Members of the C1q subfamily were cloned, and their response to infection with the grass carp virus was investigated. In the grass carp genome, 54 C1qDC genes and 67 isoforms have been identified. Most were located on chromosome 3, with 52 shared zebrafish homologies. Seven substantially differentially expressed C1qDC family genes were identified in the transcriptomes of cytokine-induced killer (CIK) cells infected with grass carp reovirus (GCRV), all of which exhibited sustained upregulation. The opening reading frames of grass carp C1qA, C1qB, and C1qC, belonging to the C1q subfamily, were determined to be 738, 732, and 735 base pairs, encoding 245, 243, and 244 amino acids with molecular weights of 25.81 kDa, 25.63 kDa and 26.16 kDa, respectively. Three genes were detected in the nine collected tissues, and their expression patterns were similar, with the highest expression levels observed in the spleen. In vivo after GCRV infection showed expression trends of C1qA, C1qB, and C1qC in the liver, spleen, and kidney. An N-type pattern in the liver and kidney was characterized by an initial increase followed by a decrease, with the highest expression occurring during the recovering period, and a V-type pattern in the spleen with the lowest expression levels during the death period. In vitro, after GCRV infection showed expression trends of C1qA, C1qB, and C1qC, and this gradually increased within the first 24 h, with a notable increase observed at the 24 h time point. After CIK cells incubation with purified recombinant proteins, rC1qA, rC1qB, and rC1qC for 3 h, followed by GCRV inoculation, the GCRV replication indicated that rC1qC exerted a substantial inhibitory effect on viral replication in CIK cells after 24 h of GCRV inoculation. These findings offer valuable insights into the structure, evolution, and function of the C1qDC family genes and provide a foundational understanding of the immune function of C1q in grass carp.

The antiviral role of largemouth bass STING against iridovirus infection.

Stimulator of interferon gene (STING) plays a crucial role in the innate immune response against viral and bacterial pathogens. However, its function in largemouth bass iridovirus (LMBV) infection remains uncertain. Here, a STING homolog (MsSTING) from largemouth bass (Micropterus salmoides) was cloned and characterized. MsSTING encoded a 407-amino-acid polypeptide, which shared 84.08% and 41.45% identity with golden perch (Perca flavescens) and human (Homo sapiens) homologs, respectively. MsSTING contained four transmembrane domains and a conserved C-terminal domain. The mRNA level of MsSTING was significantly increased in response to LMBV infection in vitro. Subcellular localization observation indicated that MsSTING encoded a cytoplasmic protein, which co-localized predominantly with endoplasmic reticulum (ER) and partially with mitochondria. Moreover, its accurate localization was dependent on the N-terminal transmembrane motif (TM) domains. MsSTING was able to activate interferon (IFN) response, evidenced by the activation of IFN1, IFN3 and ISRE promoters by its overexpression in vitro. Mutant analysis showed that both the N-terminal and C-terminal domain of MsSTING were essential for its activation on IFN response. In addition, overexpression of MsSTING inhibited the transcription and protein levels of viral core genes, indicating that MsSTING exerted antiviral action against LMBV. Consistently, the inhibitory effects were significantly attenuated when the N-terminal or C-terminal domains of MsSTING was deleted. Furthermore, MsSTING overexpression upregulated the transcriptions of interferon-related genes and pro-inflammatory factors, including TANK-binding kinase 1(TBK1), interferon regulatory factor 3 (IRF3), interferon regulatory factor 7 (IRF7), interferon stimulated exonuclease gene 20 (ISG20), interferon-induced transmembrane protein 1(IFITM1), interferon γ (IFN-γ), tumor necrosis factor α (TNF-α), interleukin 1ß (IL-1ß), and interleukin 6 (IL-6). Together, MsSTING exerted antiviral action upon LMBV infection through positive regulation the innate immune response.

Characteristics of hairtail surimi gels treated with myofibrillar protein-stabilized Pickering emulsions.

BACKGROUND: Hairtail (Trichiurus haumela) surimi exhibits poor gelation properties and a dark gray appearance, which hinder its utilization in high-quality surimi gel products. The effect of Pickering emulsions stabilized by myofibrillar proteins (MPE) on the gel properties of hairtail surimi has been unclear. In particular, the impact of MPE under NaCl and KCl treatments on the quality of hairtail surimi gels requires further elucidation. RESULTS: Pickering emulsions stabilized by myofibrillar proteins and treated with NaCl or KCl (Na-MPE, K-MPE) were added to hairtail surimi in amounts of 10-70 g kg-1. The addition of 50 g kg-1 Na-MPE and K-MPE improved the gel strength, textural properties, whiteness, and water-holding capacity (WHC) of hairtail surimi. The relative content of ß-turn and ß-sheet in the surimi gels increased and the relative content of random coils and α-helix decreased with the addition of oil. The addition of Na-MPE and K-MPE did not affect the secondary structure of surimi gels but stimulated the gelation of hairtail surimi gels. Hairtail surimi containing K-MPE demonstrated similar performance in terms of hardness, microstructure, and WHC compared with the addition of Na-MPE. CONCLUSION: The quality of hairtail surimi gels can be improved by the addition of Na-MPE or K-MPE. The K-MPE proved to be an effective option for enhancing the properties of hairtail surimi gels at 50 g kg-1 to replace Na-MPE. © 2024 Society of Chemical Industry.

Effects of Ultrasonic Power on the Structure and Rheological Properties of Skin Collagen from Albacore (Thunnus alalunga).

The effects of ultrasonic power (0, 150, 300, 450, and 600 W) on the extraction yield and the structure and rheological properties of pepsin-soluble collagen (PSC) from albacore skin were investigated. Compared with the conventional pepsin extraction method, ultrasonic treatment (UPSC) significantly increased the extraction yield of collagen from albacore skin, with a maximum increase of 8.56%. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that peptides of low molecular weight were produced when the ultrasonic power exceeded 300 W. Meanwhile, secondary structure, tertiary structure, and X-ray diffraction analyses showed that the original triple helix structure of collagen was intact after the ultrasonic treatment. The collagen solutions extracted under different ultrasonic powers had significant effects on the dynamic frequency sweep, but a steady shear test suggested that the collagen extracted at 150 W had the best viscosity. These results indicate that an ultrasonic power between 150 and 300 W can improve not only the extraction yield of natural collagen, but also the rheological properties of the collagen solution without compromising the triple helix structure.

Based on hydrogen and disulfide-mediated bonds, l-lysine and l-arginine enhanced the gel properties of low-salt mixed shrimp surimi (Antarctic krill and Pacific white shrimp).

This study delved into the effects of l-lysine (Lys) and l-arginine (Arg) on the gel properties and intermolecular interactions of low-salt (NaCl, 1 g/100 g) mixed shrimp surimi (Antarctic krill and Pacific white shrimp). The addition of Lys and Arg improved the gel strength and water holding capacity of low-salt gels, which were superior to the properties of STPP and high-salt (NaCl, 2.25 g/100 g) gels. These results can be attributed to the role of Lys and Arg in enhancing hydrogen and disulfide bonds within the low-salt gel system, promoting the solubilization of myofibrillar proteins (MP) and consequently increasing the number of MP molecules participating in gel formation. Antarctic krill MP did not show gel-forming ability and exerted a diluting effect on low-salt mixed shrimp surimi gels. Molecular docking analysis indicated the stable binding of Lys and Arg to myosin.

Tracking protein aggregation behaviour and emulsifying properties induced by structural alterations in common carp (Cyprinus carpio) myofibrillar protein during long-term frozen storage.

The effect of ultrasound-assisted immersion freezing (UIF), air freezing (AF), and immersion freezing (IF) on the protein structure, aggregation, and emulsifying properties of common carp (Cyprinus carpio) myofibrillar protein during frozen storage were evaluated in the present study. The result showed that, compared with AF and IF samples, UIF sample had higher reactive/total sulfhydryl, protein solubility, and lower protein turbidity (P < 0.05), indicating that UIF was beneficial to inhibit protein oxidation and aggregation induced by frozen storage. UIF inhibited the alteration of secondary structure and tertiary structure during frozen storage. Meanwhile, UIF sample had higher emulsifying activity index, and smaller emulsion droplet diameter than AF and IF samples (P < 0.05), suggesting that UIF was beneficial for maintaining the emulsifying properties of protein during storage. In general, UIF is a potential and effective method to suppress the decrease in protein emulsifying properties during long-term frozen storage.

Sea perch (Lateolabrax japonicus) UBC9 augments RGNNV infection by hindering RLRs-interferon response.

Small ubiquitin-like modifier (SUMO) is a reversible post-translational modification that regulates various biological processes in eukaryotes. Ubiquitin-conjugating enzyme 9 (UBC9) is the sole E2-conjugating enzyme responsible for SUMOylation and plays an important role in essential cellular functions. Here, we cloned the UBC9 gene from sea perch (Lateolabrax japonicus) (LjUBC9) and investigated its role in regulating the IFN response during red-spotted grouper nervous necrosis virus (RGNNV) infection. The LjUBC9 gene consisted of 477 base pairs and encoded a polypeptide of 158 amino acids with an active site cysteine residue and a UBCc domain. Phylogenetic analysis showed that LjUBC9 shared the closest evolutionary relationship with UBC9 from Paralichthys olivaceus. Tissue expression profile analysis demonstrated that LjUBC9 was significantly increased in multiple tissues of sea perch following RGNNV infection. Further experiments showed that overexpression of LjUBC9 significantly increased the mRNA and protein levels of RGNNV capsid protein in LJB cells infected with RGNNV, nevertheless knockdown of LjUBC9 had the opposite effect, suggesting that LjUBC9 exerted a pro-viral effect during RGNNV infection. More importantly, we found that the 93rd cysteine is crucial for its pro-viral effect. Additionally, dual luciferase assays revealed that LjUBC9 prominently attenuated the promoter activities of sea perch type Ⅰ interferon (IFN) in RGNNV-infected cells, and overexpression of LjUBC9 markedly suppressed the transcription of key genes associated with RLRs-IFN pathway. In summary, these findings elucidate that LjUBC9 impairs the RLRs-IFN response, resulting in enhanced RGNNV infection.

Identification of antibacterial activity of liver-expressed antimicrobial peptide 2 (LEAP2) from primitive vertebrate lamprey.

Liver-expressed antimicrobial peptide 2 (LEAP2) is a member of the antimicrobial peptides family and plays a key role in the innate immune system of organisms. LEAP2 orthologs have been identified from a variety of fish species, however, its function in primitive vertebrates has not been clarified. In this study, we cloned and identified Lc-LEAP2 from the primitive jawless vertebrate lamprey (Lethenteron camtschaticum) which includes a 25 amino acids signal peptide and a mature peptide of 47 amino acids. Although sequence similarity was low compared to other species, the mature Lc-LEAP2 possesses four conserved cysteine residues, forming a core structure with two disulfide bonds between the cysteine residues in the relative 1-3 (Cys 58 and Cys 69) and 2-4 (Cys 64 and Cys 74) positions. Lc-LEAP2 was most abundantly expressed in the muscle, supraneural body and buccal gland of lamprey, and was significantly upregulated during LPS and Poly I:C stimulations. The mature peptide was synthesized and characterized for its antibacterial activity against different bacteria. Lc-LEAP2 possessed inhibition of a wide range of bacteria with a dose-dependence, disrupting the integrity of bacterial cell membranes and binding to bacterial genomic DNA, although its inhibitory function is weak compared to that of higher vertebrates. These data suggest that Lc-LEAP2 plays an important role in the innate immunity of lamprey and is of great value in improving resistance to pathogens. In addition, the antimicrobial mechanism of LEAP2 has been highly conserved since its emergence in primitive vertebrates.

Characterization and functional analysis of SOCS9 from orange-spotted grouper (Epinephelus coioides) during virus infection.

The suppressor of cytokine signaling (SOCS) proteins family have twelve members including eight known mammalian SOCS members (CISH, SOCS1-7) and four new discovery members (SOCS3b, SOCS5b, SOCS8 and SOCS9) that is regarded as a classic feedback inhibitor of cytokine signaling. Although the function of the mammalian SOCS proteins have been well studied, little is known about the roles of SOCS in fish during viral infection. In this study, the molecular characteristics of SOCS9 from orange-spotted grouper (Epinephelus coioides, EcSOCS9) is investigated. The EcSOCS9 protein encoded 543 amino acids with typical SH2 (389-475aa) and SOCS_box (491-527aa), sharing high identities with reported fish SOCS9. EcSOCS9 was expressed in all detected tissues and highly expressed in kidney. After red-spotted grouper nervous necrosis virus (RGNNV) infection, the expression of EcSOCS9 was significantly induced in vitro. Furthermore, EcSOCS9 overexpression enhanced RGNNV replication, promoted virus-induced mitophagy that evidenced by the increased level of LC3-Ⅱ, BCL2, PGAM5 and decreased level of BNIP3 and FUNDC1. Besides, EcSOCS9 overexpression suppressed the expression levels of ATP6, CYB, ND4, ATP level and induced ROS level. The expression levels of interferon (IFN) related factors (IRF1, IRF3, IRF7, P53), inflammatory factors (IL1-ß, IL8, TLR2, TNF-α) and IFN-3, ISRE, NF-κB, AP1 activities were also reduced by overexpressing EcSOCS9. These date suggests that EcSOCS9 impacts RGNNV infection through modulating mitophagy, regulating the expression levels of IFN- related and inflammatory factors, which will expand our understanding of fish immune responses during viral infection.

Involvement of tumor necrosis factor receptor-associated factor 6 (TRAF6) in NF-κB activation and antiviral immunity: Molecular and functional characterization of TRAF6 in red-spotted grouper (Epinephelus akaara).

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a member of the TRAF family of adaptor proteins involved in the signal transduction pathways of both TNF receptor and interleukin-1 receptor/Toll-like receptor superfamilies. In this study, red-spotted grouper (Epinephelus akaara) TRAF6 (EaTraf6) was identified and characterized. The open reading frame of EaTraf6, 1713 bp in length, encodes a putative protein of 570 amino acids and has a predicted molecular weight and theoretical isoelectric point of 64.11 kDa and 6.07, respectively. EaTraf6 protein contains an N-terminal RING-type zinc finger domain, two TRAF-type zinc finger domains, a coiled-coil region (zf-TRAF), and a conserved C-terminal meprin and TRAF homology (MATH) domain. EaTraf6 shared the highest amino acid sequence identity with its ortholog from Epinephelus coioides, and phylogenetic analysis showed all fish TRAF6s clustered together and apart from other species. qRT-PCR results revealed that EaTraf6 was ubiquitously expressed in all examined tissues, with the highest level detected in the blood. In the immune challenge, EaTraf6 exhibited modulated mRNA expression levels in the blood and spleen. The subcellular localization analysis revealed that the EaTraf6 protein was predominantly present in the cytoplasm; however, it could translocate into the nucleus following poly (I:C) stimulation. The antiviral function of EaTraf6 was confirmed by analyzing the expression of host antiviral genes and viral genomic RNA during viral hemorrhagic septicemia virus infection. Additionally, luciferase reporter assay results indicated that EaTraf6 is involved in the activation of the NF-κB signaling pathway upon poly (I:C) stimulation. Finally, the effect of EaTraf6 on cytokine gene expression and its role in regulating macrophage M1 polarization were demonstrated. Collectively, these findings suggest that EaTraf6 is a crucial immune-related gene that significantly contributes to antiviral functions and regulation of NF-κB activity in the red-spotted grouper.

Insights into the potential mechanism of liquid nitrogen spray freezing's influence on volatile compounds in surimi gels with different cross-linking degrees: Focus on oxidation, protein structure, intermolecular force and free amino acid alterations.

This study revealed the variations in odor characteristics and underlying mechanisms of different cross-linked surimi gels under liquid nitrogen (LN) spray freezing. The results demonstrated that LN spray freezing had an essential effect on the gels' odor. The odor changes in the -80 °C LN spray freezing group were closer to the control group, while -35 °C LN spray freezing treatment had the greatest impact on the aroma quality of gels. Freezing reduced gels' texture properties, intensified lipid and protein oxidation, altered protein conformation, increased surface hydrophobicity and hydrophobic interactions. These changes affected the gels' odor characteristics, leading to a reduction in fish aroma and an increase in fishy and oil odors after freezing. These tendencies were more pronounced at -35 °C LN spray freezing with lower cross-linking degrees, and reducing the freezing temperature to -80 °C and increasing the cross-linking degree to 62.99% mitigated the extent of deterioration in gel flavor quality.

Characterization of type II IFNs and their receptors in a cyprinid fish, the blunt snout bream Megalobrama amblycephala.

Type II interferons (IFNs) are a key class of molecules regulating innate and adaptive immunity in vertebrates. In the present study, two members of the type II IFNs, IFN-γ and IFNγ-rel, were identified in the blunt snout bream (Megalobrama amblycephala). The open reading frame (ORF) of IFN-γ and IFNγ-rel was found to have 564 bp and 492 bp, encoding 187 and 163 amino acids, with the first 26 and 24 amino acids being the signal peptide, respectively. IFN-γ and IFNγ-rel genes showed a high degree of similarity to their zebrafish homologues, being 76.9 % and 58.9 %, respectively. In the phylogenetic tree, IFN-γ and IFNγ-rel were clustered with homologous genes in cyprinids. In blunt snout bream, IFN-γ and IFNγ-rel were constitutively expressed in trunk kidney, head kidney, spleen, liver, heart, muscle, gill, intestine and brain and were significantly up-regulated by poly (I:C) induction in head kidney, spleen, liver, gill and intestine. Using recombinant proteins of IFN-γ and IFNγ-rel, the surface plasmon resonance (SPR) results showed that IFN-γ was bound to CRFB6, CRFB13 and CRFB17, but mainly to CRFB6 and CRFB13, whereas IFN-γrel bound mainly to CRFB17 and had no affinity with CRFB6. These results contribute to a better understanding on type II IFNs and their receptor usage in teleost fish.

A CD6 homolog of Nile tilapia (Oreochromis niloticus) conserved binding bacteria involved in the regulation of Streptococcus agalactiae induced inflammation.

As a lymphocyte-specific surface receptor belonging to the cysteine-rich superfamily of scavenger receptors, CD6 acts as a pattern recognition receptor for microbial components and is involved in the regulation of inflammatory responses. However, the characteristics and functions of CD6 molecules in lower vertebrates represented by teleost fish are unknown. In this study, a CD6 homolog (designated OnCD6) was characterized from Nile tilapia (Oreochromis niloticus), and establishing its role as a PRRs that participates in immune recognition. OnCD6 contains an open reading frame of 1872 bp that encodes a peptide of 623 amino acids, and contains two conserved SR domain. Multiple sequence alignment revealed that OnCD6 shares a relatively high level of identity with those of other species. Transcriptional expression analysis revealed that OnCD6 was constitutively expressed in immunes tissues such as head kidney and thymus. The expression level of OnCD6 in mainly immune tissues were found significantly upregulated after the injection of Streptococcus agalactiae (S. agalactiae). Moreover, OnCD6 protein was located in the head kidney and brain, mainly over the plasma membrane of lymphocytes in these immune tissues. In vitro experiments showed that CD6 extracellular protein bound to and aggregated several Gram-positive and -negative bacterial strains through the recognition of bacterial surface conserved components LPS and LTA etc. In vivo experiments demonstrated that overexpression OnCD6 before S. agalactiae challenge significantly improved tilapia survival, and this was concomitant with reduced bacterial load and pro-inflammatory cytokines (IL-1ß and TNF-α). Taken together, our results illustrated the function of CD6 molecular pattern recognition receptors (PRRs) is conserved and plays an important role in antibacterial infection.

Cloning, expression and functional characterization of recombinant tumor necrosis factor α1 (TNFα1) from white crucian carp in gut immune regulation.

TNFα is one of important cytokines belonging to TNF superfamily, which can exhibit a pleiotropic effect in immune modulation, homeostasis as well as pathogenesis. However, its immunoregulatory function on mucosal immunity in fish gut are still unclear. In this study, we aimed to investigated the immunoregulatory role of TNFα1 in midgut of white crucian carp (WCC). WCC-TNFα1 sequence and its deduced structure were firstly identified in WCC. Then, tissue-specific analysis revealed that high-level WCC-TNFα1 expression was detected in gill. After Aeromonas hydrophila and lipopolysaccharide (LPS) stimulated, increased trends of WCC-TNFα1 expressions were detected in immune-related tissues and cultured fish cells, respectively. WCC anal-intubated with WCC-TNFα1 fusion protein showed the increased levels of edema and fuzzy appearance in impaired villi, along with atrophy and reduction of goblet cells (GC). Moreover, the expression levels of tight junction (TJ) genes and mucin genes were consistently lower than those of the control (P < 0.05). WCC-TNFα1 treatment could sharply decrease antioxidant status in midgut, while the expression levels of caspase (CASP) genes, unfolded protein response (UPR) genes and redox response genes increased dramatically. Our results suggested that WCC-TNFα1 could exhibit a detrimental effect on antioxidant and mucosal immune regulation in midgut of WCC.

Improvement of gelation properties of Penaeus vannamei surimi by magnetic field-assisted freezing in combination with curdlan.

Traditional methods of freezing and thawing may harm the quality of meat products. In order to reduce the negative impact of freezing on surimi products, the magnetic field-assisted freezing method is combined with various curdlan ratios to enhance the gelation characteristics of Penaeus vannamei surimi in this study. The results showed that the magnetic field-assisted freezing technique significantly improved the quality of thawed surimi compared with soaking freezing (SF), whereas the addition of curdlan further improved the gelation properties, and the gel strength, water-holding capacity, textural properties, whiteness, and G' value were significantly improved when its content was increased to 0.6 %. However, excessive amounts of curdlan interfered with protein covalent cross-linking, leading to a decrease in gel quality. Additionally, the addition of magnetic field and curdlan encouraged the shift of the α-helix to the random coil and ß-sheet transition, which stimulated the growth of myofibril molecules, exposed the hydrophobic groups and thiols, improved protein-molecule interactions, and promoted systematic gathering of proteins, leading to the formation of the microstructure of dense and small pores. It also resulted in a drop in water release, an increase in the proton density and a shift in the water condition from free water to more immobile water, which had higher sensory qualities. These effects together resulted in a reduction in thawing and cooking loss to 11.41 % and 13.83 %, respectively. These results also help to clarify the gelation process of shrimp surimi and help to regulate the gelation characteristics of shrimp surimi products.

Identification of antimicrobial peptide genes from transcriptomes in Mandarin fish (Siniperca chuatsi) and their response to infection with Aeromonas hydrophila.

Mandarin fish (Siniperca chuatsi) is a valuable freshwater fish species widely cultured in China. Its aquaculture production is challenged by bacterial septicaemia, which is one of the most common bacterial diseases. Antimicrobial peptides (AMPs) play a critical role in the innate immune system of fish, exhibiting defensive and inhibitory effects against a wide range of pathogens. This study aimed to identify the antimicrobial peptide genes in mandarin fish using transcriptomes data obtained from 17 tissue in our laboratory. Through nucleotide sequence alignment and protein structural domain analysis, 15 antimicrobial peptide genes (moronecidin, pleurocidin, lysozyme g, thymosin ß12, hepcidin, leap 2, ß-defensin, galectin 8, galectin 9, apoB, apoD, apoE, apoF, apoM, and nk-lysin) were identified, of which 9 antimicrobial peptide genes were identified for the first time. In addition, 15 AMPs were subjected to sequence characterization and protein structure analysis. After injection with Aeromonas hydrophila, the number of red blood cells, hemoglobin concentration, and platelet counts in mandarin fish showed a decreasing trend, indicating partial hemolysis. The expression change patterns of 15 AMP genes in the intestine after A. hydrophila infection were examined by using qRT-PCR. The results revealed, marked up-regulation (approximately 116.04) of the hepcidin gene, down-regulation of the piscidin family genes expression. Moreover, most AMP genes were responded in the early stages after A. hydrophila challenge. This study provides fundamental information for investigating the role of the different antimicrobial peptide genes in mandarin fish in defense against A. hydrophila infection.

Insight into the effect of large yellow croaker roe phospholipids on the physical properties of surimi gel and their interaction mechanism with myofibrillar protein.

BACKGROUND: The present study aimed to investigate the effects of large yellow croaker roe phospholipids (LYCRPLs) on the physical properties of surimi gels and to clarify their interaction mechanism with myofibrillar proteins (MPs) in terms of chemical forces and the spatial conformation. RESULTS: LYCRPLs could improve the gel strength, textural properties, rheological properties and water-holding capacity of surimi gels. Moreover, the interaction mechanism between LYCRPLs with MPs was revealed through intermolecular forces, Fourier transform infrared spectroscopy and ultraviolet visible absorption spectroscopy. The findings demonstrated that LYCRPLs enhanced the surface hydrophobicity and particle size of MPs, facilitating expansion and cross-linking of MPs. CONCLUSION: These results provide a theoretical basis for improving the characteristics of surimi gels and thus facilitate the application of LYCRPLs in the aquatic food industry. © 2023 Society of Chemical Industry.