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.

Feedback loop regulation between viperin and viral hemorrhagic septicemia virus through competing protein degradation pathways.

Viperin is an antiviral protein that exhibits a remarkably broad spectrum of antiviral activity. Viperin-like proteins are found all kingdoms of life, suggesting it is an ancient component of the innate immune system. However, viruses have developed strategies to counteract viperin's effects. Here, we describe a feedback loop between viperin and viral hemorrhagic septicemia virus (VHSV), a common fish pathogen. We show that Lateolabrax japonicus viperin (Ljviperin) is induced by both IFN-independent and IFN-dependent pathways, with the C-terminal domain of Ljviperin being important for its anti-VHSV activity. Ljviperin exerts an antiviral effect by binding both the nucleoprotein (N) and phosphoprotein (P) of VHSV and induces their degradation through the autophagy pathway, which is an evolutionarily conserved antiviral mechanism. However, counteracting viperin's activity, N protein targets and degrades transcription factors that up-regulate Ljviperin expression, interferon regulatory factor (IRF) 1 and IRF9, through ubiquitin-proteasome pathway. Together, our results reveal a previously unknown feedback loop between viperin and virus, providing potential therapeutic targets for VHSV prevention. Importance: Viral hemorrhagic septicaemia (VHS) is a contagious disease caused by the viral hemorrhagic septicaemia virus (VHSV), which poses a threat to over 80 species of marine and freshwater fish. Currently, there are no effective treatments available for this disease. Understanding the mechanisms of VHSV-host interaction is crucial for preventing viral infections. Here, we found that, as an ancient antiviral protein, viperin degrades the N and P proteins of VHSV through the autophagy pathway. Additionally, the N protein also impacts the biological functions of IRF1 and IRF9 through the ubiquitin-proteasome pathway, leading to the suppression of viperin expression. Therefore, the N protein may serve as a potential virulence factor for the development of VHSV vaccines and screening of antiviral drugs. Our research will serve as a valuable reference for the development of strategies to prevent VHSV infections.

Viruses in deep-sea cold seep sediments harbor diverse survival mechanisms and remain genetically conserved within species.

Deep sea cold seep sediments have been discovered to harbor novel, abundant, and diverse bacterial and archaeal viruses. However, little is known about viral genetic features and evolutionary patterns in these environments. Here, we examined the evolutionary ecology of viruses across active and extinct seep stages in the area of Haima cold seeps in the South China Sea. A total of 338 viral operational taxonomic units are identified and linked to 36 bacterial and archaeal phyla. The dynamics of host-virus interactions are informed by diverse antiviral defense systems across 43 families found in 487 microbial genomes. Cold seep viruses are predicted to harbor diverse adaptive strategies to persist in this environment, including counter-defense systems, auxiliary metabolic genes, reverse transcriptases, and alternative genetic code assignments. Extremely low nucleotide diversity is observed in cold seep viral populations, being influenced by factors including microbial host, sediment depth, and cold seep stage. Most cold seep viral genes are under strong purifying selection with trajectories that differ depending on whether cold seeps are active or extinct. This work sheds light on the understanding of environmental adaptation mechanisms and evolutionary patterns of viruses in the sub-seafloor biosphere.

Methyltransferase-like 3 suppresses red spotted grouper nervous necrosis virus and viral hemorrhagic septicemia virus infection by enhancing type I interferon responses in sea perch.

Methylation at the N6 position of adenosine (m6A) is the most abundant internal mRNA modification in eukaryotes, tightly associating with regulation of viral life circles and immune responses. Here, a methyltransferase-like 3 homolog gene from sea perch (Lateolabrax japonicus), designated LjMETTL3, was cloned and characterized, and its negative role in fish virus pathogenesis was uncovered. The cDNA of LjMETTL3 encoded a 601-amino acid protein with a MT-A70 domain, which shared the closest genetic relationship with Echeneis naucrates METTL3. Spatial expression analysis revealed that LjMETTL3 was more abundant in the immune tissues of sea perch post red spotted grouper nervous necrosis virus (RGNNV) or viral hemorrhagic septicemia virus (VHSV) infection. LjMETTL3 expression was significantly upregulated at 12 and 24 h post RGNNV and VHSV infection in vitro. In addition, ectopic expression of LjMETTL3 inhibited RGNNV and VHSV infection in LJB cells at 12 and 24 h post infection, whereas knockdown of LjMETTL3 led to opposite effects. Furthermore, we found that LjMETTL3 may participate in boosting the type I interferon responses by interacting with TANK-binding kinase. Taken together, these results disclosed the antiviral role of fish METTL3 against RGNNV and VHSV and provided evidence for understanding the potential mechanisms of fish METTL3 in antiviral innate immunity.

Molecular characterization, transcriptional regulation of sea perch Moloney leukemia virus 10 and its antiviral function against VHSV.

Moloney leukemia virus 10 (MOV10) is a conserved RNA helicase and has multiple biological functions in mammals, but its role remains poorly understood in bony fish. Here, we cloned a MOV10 homolog from sea perch (Lateolabrax japonicus), which contained 23 exons and 22 introns, with an open reading frame of 3000 bp encoding 1000 amino acids. Tissue distribution analysis showed that MOV10 was high expressed in blood of sea perch. Promoter analysis revealed several putative multiple transcription factors binding sites, including upstream transcription factor 1, GATA-box, transcription initiation factor IIB, activator protein 1 and two interferon (IFN) stimulated response elements. Further analysis found that IFNc, IFNh, and IFNγ could not only activate IFN regulatory factor (IRF) 1 expression which in turn led to the induction of MOV10, but also prompted the expression of IRF10 to hinder excessive MOV10 expression. Moreover, IRF2 also suppressed MOV10 expression that was initiated by IRF1. Viral hemorrhagic septicemia virus (VHSV) infection upregulated MOV10 expression in vivo and in vitro, which in turn, enhanced IFNh expression and exhibited strong antiviral activity against VHSV proliferation. This study provides a basis to investigate the immune escape of VHSV by affecting the biological function of transcription factors in the signaling pathways associated with antiviral molecules.

Ring Finger Protein 34 Facilitates Nervous Necrosis Virus Evasion of Antiviral Innate Immunity by Targeting TBK1 and IRF3 for Ubiquitination and Degradation in Teleost Fish.

Ubiquitination, as one of the most prevalent posttranslational modifications of proteins, enables a tight control of host immune responses. Many viruses hijack the host ubiquitin system to regulate host antiviral responses for their survival. Here, we found that the fish pathogen nervous necrosis virus (NNV) recruited Lateolabrax japonicus E3 ubiquitin ligase ring finger protein 34 (LjRNF34) to inhibit the RIG-I-like receptor (RLR)-mediated interferon (IFN) response via ubiquitinating Lateolabrax japonicus TANK-binding kinase 1 (LjTBK1) and interferon regulatory factor 3 (LjIRF3). Ectopic expression of LjRNF34 greatly enhanced NNV replication and prevented IFN production, while deficiency of LjRNF34 led to the opposite effect. Furthermore, LjRNF34 targeted LjTBK1 and LjIRF3 via its RING domain. Of note, the interactions between LjRNF34 and LjTBK1 or LjIRF3 were conserved in different cellular models derived from fish. Mechanically, LjRNF34 promoted K27- and K48-linked ubiquitination and degradation of LjTBK1 and LjIRF3, which in turn diminished LjTBK1-induced translocation of LjIRF3 from the cytoplasm to the nucleus. Ultimately, NNV capsid protein (CP) was found to bind with LjRNF34, CP induced LjTBK1 and LjIRF3 degradation, and IFN suppression depended on LjRNF34. Our finding demonstrates a novel mechanism by which NNV CP evaded host innate immunity via LjRNF34 and provides a potential drug target for the control of NNV infection. IMPORTANCE Ubiquitination plays an essential role in the regulation of innate immune responses to pathogens. NNV, a type of RNA virus, is the causal agent of a highly destructive disease in a variety of marine and freshwater fish. A previous study reported NNV could hijack the ubiquitin system to manipulate the host's immune responses; however, how NNV utilizes ubiquitination to facilitate its own replication is not well understood. Here, we identified a novel distinct role of E3 ubiquitin ligase LjRNF34 as an IFN antagonist to promote NNV infection. NNV capsid protein utilized LjRNF34 to target LjTBK1 and LjIRF3 for K27- and K48-linked ubiquitination and degradation. Importantly, the interactions between LjRNF34 and CP, LjTBK1, or LjIRF3 are conserved in different cellular models derived from fish, suggesting it is a general immune evasion strategy exploited by NNV to target the IFN response via RNF34.

Evolutionary ecology of microbial populations inhabiting deep sea sediments associated with cold seeps.

Deep sea cold seep sediments host abundant and diverse microbial populations that significantly influence biogeochemical cycles. While numerous studies have revealed their community structure and functional capabilities, little is known about genetic heterogeneity within species. Here, we examine intraspecies diversity patterns of 39 abundant species identified in sediment layers down to 430 cm below the sea floor across six cold seep sites. These populations are grouped as aerobic methane-oxidizing bacteria, anaerobic methanotrophic archaea and sulfate-reducing bacteria. Different evolutionary trajectories are observed at the genomic level among these physiologically and phylogenetically diverse populations, with generally low rates of homologous recombination and strong purifying selection. Functional genes related to methane (pmoA and mcrA) and sulfate (dsrA) metabolisms are under strong purifying selection in most species investigated. These genes differ in evolutionary trajectories across phylogenetic clades but are functionally conserved across sites. Intrapopulation diversification of genomes and their mcrA and dsrA genes is depth-dependent and subject to different selection pressure throughout the sediment column redox zones at different sites. These results highlight the interplay between ecological processes and the evolution of key bacteria and archaea in deep sea cold seep extreme environments, shedding light on microbial adaptation in the subseafloor biosphere.

A Novel Inovirus Reprograms Metabolism and Motility of Marine Alteromonas.

Members from the Inoviridae family with striking features are widespread, highly diverse, and ecologically pervasive across multiple hosts and environments. However, a small number of inoviruses have been isolated and studied. Here, a filamentous phage infecting Alteromonas abrolhosensis, designated ϕAFP1, was isolated from the South China Sea and represented a novel genus of Inoviridae. ϕAFP1 consisted of a single-stranded DNA genome (5986 bp), encoding eight putative ORFs. Comparative analyses revealed ϕAFP1 could be regarded as genetic mosaics having homologous sequences with Ralstonia and Stenotrophomonas phages. The temporal transcriptome analysis of A. abrolhosensis to ϕAFP1 infection revealed that 7.78% of the host genes were differentially expressed. The genes involved in translation processes, ribosome pathways, and degradation of multiple amino acid pathways at the plateau period were upregulated, while host material catabolic and bacterial motility-related genes were downregulated, indicating that ϕAFP1 might hijack the energy of the host for the synthesis of phage proteins. ϕAFP1 exerted step-by-step control on host genes through the appropriate level of utilizing host resources. Our study provided novel information for a better understanding of filamentous phage characteristics and phage-host interactions. IMPORTANCE Alteromonas is widely distributed and plays a vital role in biogeochemical in marine environments. However, little information about Alteromonas phages is available. Here, we isolated and characterized the biological characteristics and genome sequence of a novel inovirus infecting Alteromonas abrolhosensis, designated ϕAFP1, representing a novel viral genus of Inoviridae. We then presented a comprehensive view of the ϕAFP1 phage-Alteromonas abrolhosensis interactions, elucidating reprogramed host metabolism and motility. Our study provided novel information for better comprehension of filamentous phage characteristics and phage-host interactions.

Sea perch (Lateolabrax japonicus) autophagy related gene 5 promotes RGNNV infection via inhibiting RLRs-interferon signaling pathway.

Autophagy-related gene 5 (Atg5), an essential component of autophagy machinery, is associated with innate immune responses. Here, the Atg5 of sea perch (Lateolabrax japonicus) (LjAtg5) was cloned and its role in regulating autophagy and interferon (IFN) response during red-spotted grouper nervous necrosis virus (RGNNV) infection was investigated. The LjAtg5 cDNA encoded a polypeptide of 275 amino acids with an APG5 domain, and had the closet genetic relationship with Micropterus salmoides Atg5. Autophagic detection showed LjAtg5 was conserved in inducing cell autophagy. Spatial expression analysis revealed LjAtg5 had a higher expression level in liver, brain, and kidney tissues of RGNNV-infected sea perch compared with the control group. In RGNNV-infected LJB cells, overexpression of LjAtg5 significantly increased the mRNA and protein levels of capsid protein, whereas knockdown of LjAtg5 led to the opposite effect, indicating LjAtg5 played a pro-viral role during RGNNV infection. Furthermore, dual luciferase reporter assay revealed LjAtg5 significantly suppressed the activation of sea perch type I IFN promoter in vitro, and overexpression of LjAtg5 strongly weaken the expression of genes related to the RIG-I-like receptors (RLRs) signaling pathway and IFN stimulated genes. These results suggested LjAtg5 promoted RGNNV infection by negatively regulating RLRs-IFN signaling pathway.

The Capsid Protein of Nervous Necrosis Virus Antagonizes Host Type I IFN Production by a Dual Strategy to Negatively Regulate Retinoic Acid-Inducible Gene-I-like Receptor Pathways.

Nervous necrosis virus (NNV), a highly pathogenic RNA virus, is a major pathogen in the global aquaculture industry. To efficiently infect fish, NNV must evade or subvert the host IFN for their replication; however, the precise mechanisms remain to be elucidated. In this study, we reported that capsid protein (CP) of red-spotted grouper NNV (RGNNV) suppressed the IFN antiviral response to promote RGNNV replication in Lateolabrax japonicus brain cells, which depended on the ARM, S, and P domains of CP. CP showed an indirect or direct association with the key components of retinoic acid-inducible gene-I-like receptors signaling, L. japonicus TNFR-associated factor 3 (LjTRAF3) and IFN regulatory factor (LjIRF3), respectively, and degraded LjTRAF3 and LjIRF3 through the ubiquitin-proteasome pathway in HEK293T cells. Furthermore, we found that CP potentiated LjTRAF3 K48 ubiquitination degradation in a L. japonicus ring finger protein 114-dependent manner. LjIRF3 interacted with CP through the S domain of CP and the transcriptional activation domain or regulatory domain of LjIRF3. CP promoted LjIRF3 K48 ubiquitination degradation, leading to the reduced phosphorylation level and nuclear translocation of LjIRF3. Taken together, we demonstrated that CP inhibited type I IFN response by a dual strategy to potentiate the ubiquitination degradation of LjTRAF3 and LjIRF3. This study reveals a novel mechanism of RGNNV evading host immune response via its CP protein that will provide insights into the complex pathogenesis of NNV.

Nectin4 antagonises type I interferon production by targeting TRAF3 for autophagic degradation and disrupting TRAF3-TBK1 complex formation.

Autophagy, a conserved cellular degradative process, plays a crucial role in innate immunity during viral infections. Nervous necrosis virus (NNV), a leading cause of fish diseases with morbidity and mortality, triggers cell autophagy to promote viral replication; however, the details of how NNV utilises autophagy to facilitate its own replication remain largely unexplored. Here, we investigated the mechanism by which the sea perch Nectin4 (LjNectin4), a receptor of NNV, regulates autophagy and the innate immune system by targeting TNFR-associated factor 3 (TRAF3). Our data demonstrated that LjNectin4 directly binds to the NNV capsid protein and facilitates NNV entry, indicating that LjNectin4 functions as an NNV receptor. Moreover, LjNectin4 promoted NNV replication by inhibiting key elements of the RLR signalling pathway (MDA5, MAVS, TRAF3, TBK1, and IRF3)-induced IFN response. Mechanistically, LjNectin4 directly interacted with TRAF3 and promoted its autophagy-mediated lysosomal degradation. Domain mapping of the interaction between TRAF3 and LjNectin4 or TBK1 showed that both LjNectin4 and TBK1 interacted with the ZF2 and TRAF-C domains of TRAF3, suggesting that LjNectin4 blocked TRAF3-TBK1 complex formation. Collectively, our study revealed that NNV utilises LjNectin4 to suppress IFN production by mediating TRAF3 autophagic degradation and disrupting the TRAF3-TBK1 complex, thereby promoting NNV replication.

Production of functional sperm from in vitro-cultured premeiotic spermatogonia in a marine fish.

In vitro production of functional gametes can revolutionize reproduction by reducing generation intervals and accelerating genetic breeding in aquaculture, especially in fish with relatively long generations. Nevertheless, functional sperm production from in vitro-cultured spermatogonia remains a challenge in most aquaculture fish. In this study, we isolated and characterized premeiotic spermatogonia from marine four-eyed sleepers ( Bostrychus sinensis), which are prone to ovotesticular or sterile testicular development, and induced the differentiation of the spermatogonia into flagellated sperm in a three-dimensional (3D) culture system. Artificial insemination indicated that the in vitro-derived sperm were capable of fertilizing mature oocytes to develop into normal larvae. Furthermore, melatonin significantly promoted spermatogonia proliferation and differentiation through the ERK1/2 signaling pathway, and thus increased the efficiency in functional sperm production. The 3D culture system and resulting functional sperm hold great promise for improving the genetic breeding of aquaculture fish.

N Protein of Viral Hemorrhagic Septicemia Virus Suppresses STAT1-Mediated MHC Class II Transcription to Impair Antigen Presentation in Sea Perch, Lateolabrax japonicus.

Upon virus invasion of the host, APCs process Ags to short peptides for presentation by MHC class II (MHC-II). The recognition of virus-derived peptides in the context of MHC-II by CD4+ T cells initiates the adaptive immune response for virus clearance. As a survival instinct, viruses have evolved mechanisms to evade Ag processing and presentation. In this study, we discovered that IFN-γ induced endogenous MHC-II expression by a sea perch brain cell line through the STAT1/IFN regulatory factor 1 (IRF1)/CIITA signaling pathway. Furthermore, viral hemorrhagic septicemia virus infection significantly inhibited the IFN-γ-induced expression of IRF1, CIITA, MHC-II-α, and MHC-II-ß genes. By contrast, although STAT1 transcript was upregulated, paradoxically, the STAT1 protein level was attenuated. Moreover, overexpression analysis revealed that viral hemorrhagic septicemia virus N protein blocked the IFN-γ-induced expression of IRF1, CIITA, MHC-II-α, and MHC-II-ß genes, but not the STAT1 gene. We also found out that N protein interacted with STAT1 and enhanced the overall ubiquitination level of proteins, including STAT1 in Lateolabrax japonicus brain cells. Enhanced ubiquitination of STAT1 through K48-linked ubiquitination led to its degradation through the ubiquitin-proteasome pathway, thereby inhibiting the biological function of STAT1. Our study suggests that aquatic viruses target Ag presentation in lower vertebrates for immune evasion as do mammalian viruses.

Establishment and characterization of a liver cell line, ALL, derived from yellowfin sea bream, Acanthopagrus latus, and its application to fish virology.

Yellowfin sea bream (Acanthopagrus latus) is an important economic fish, which is seriously threatened by various fish viruses. In this study, a cell line designated as ALL derived from the liver of yellowfin sea bream was developed and characterized. The cell line grew well in Dulbecco's modified Eagle's medium containing 10%-20% foetal bovine serum at 28°C. Amplification of the cytochrome B gene indicated that ALL cells originated from yellowfin sea bream. The modal chromosome number of ALL cells was 48. ALL cells were efficiently transfected with pEGFP-N3 plasmids, indicating the potential application of ALL cells in exogenous gene manipulation studies. ALL cells were susceptive to three main fish viruses, including viral haemorrhagic septicaemia virus (VHSV), red-spotted grouper nervous necrosis virus (RGNNV) and largemouth bass virus (LMBV). The replication of VHSV, RGNNV and LMBV in ALL cells was confirmed by quantitative real-time polymerase chain reaction, virus titre and transmission electron microscopy assays. Moreover, ALL cells could respond to VHSV, RGNNV and LMBV infections, as indicated by the differential expression of antiviral genes involving in the innate immune response. In conclusion, the newly established ALL cell line will be an excellent in vitro platform for the study of the virus-yellowfin sea bream interaction.

Capsid protein from red-spotted grouper nervous necrosis virus induces incomplete autophagy by inactivating the HSP90ab1-AKT-MTOR pathway.

As a highly important fish virus, nervous necrosis virus (NNV) has caused severe economic losses to the aquaculture industry worldwide. Autophagy, an evolutionarily conserved intracellular degradation process, is involved in the pathogenesis of several viruses. Although NNV can induce autophagy to facilitate infection in grouper fish spleen cells, how it initiates and mediates autophagy pathways during the initial stage of infection is still unclear. Here, we found that red-spotted grouper NNV (RGNNV) induced autophagosome formation in two fish cell lines at 1.5 and 3 h post infection, indicating that autophagy is activated upon entry of RGNNV. Moreover, autophagic detection showed that RGNNV entry induced incomplete autophagy by impairing the fusion of autophagosomes with lysosomes. Further investigation revealed that binding of the RGNNV capsid protein (CP) to the Lateolabrax japonicus heat shock protein HSP90ab1 (LjHSP90ab1), a cell surface receptor of RGNNV, contributed to RGNNV invasion-induced autophagy. Finally, we found that CP blocked the interaction of L. japonicus protein kinase B (AKT) with LjHSP90ab1 by competitively binding the NM domain of LjHSP90ab1 to inhibit the AKT-mechanistic target of the rapamycin (MTOR) pathway. This study provides novel insight into the relationship between NNV receptors and autophagy, which may help clarify the pathogenesis of NNV.

Proper Balance of Small GTPase rab10 Is Critical for PGC Migration in Zebrafish.

MicroRNAs (miRNAs) play important roles in post-transcriptional repression in nearly every biological process including germ cell development. Previously, we have identified a zebrafish germ plasm-specific miRNA miR-202-5p, which regulates PGC migration through targeting cdc42se1 to protect cdc42 expression. However, knockdown of cdc42se1 could not significantly rescue PGC migration in maternal miR-202 mutant (MmiR-202) embryos, indicating that there are other target genes of miR-202-5p required for the regulation of PGC migration. Herein, we revealed the transcriptional profiles of wild type and MmiR-202 PGCs and obtained 129 differentially expressed genes (DEGs), of which 42 DEGs were enriched cell migration-related signaling pathways. From these DEGs, we identified two novel miR-202-5p target genes prdm12b and rab10. Furthermore, we found that disruption of rab10 expression led to significantly migratory defects of PGC by overexpression of rab10 siRNA, or WT, inactive as well as active forms of rab10 mRNA, and WT rab10 overexpression mediated migratory defects could be partially but significantly rescued by overexpression of miR-202-5p, demonstrating that rab10 is an important factor involved miR-202-5p mediated regulation of PGC migration. Taken together, the present results provide significant information for understanding the molecular mechanism by which miR-202-5p regulates PGC migration in zebrafish.

The CXC Chemokine Receptors in Four-Eyed Sleeper (Bostrychus sinensis) and Their Involvement in Responding to Skin Injury.

CXC Chemokine signaling plays an important role in wound healing. The four-eyed sleeper (Bostrychus sinensis) is a commercially important marine fish, which is prone to suffer skin ulceration at high temperature seasons, leading to mass mortality of fish in aquaculture farms. The genetic background related to skin ulceration and wound healing has remained unknown in this fish. Herein, we identified 10 differentially expressed Bostrychus sinensis CXC chemokine receptors (BsCXCRs) in skin ulcerated fish by de novo transcriptome sequencing. The transcripts of these BsCXCRs were classified in seven types, including BsCXCR1a/1b, BsCXCR2, BsCXCR3a1/3a2, BsCXCR4a/4b, and BsCXCR5-7, and BsCXCR6 was the first CXCR6 homologue experimentally identified in teleost fish. These BsCXCRs were further characterized in gene and protein structures, as well as phylogenetics, and the results revealed that BsCXCRs have expanded to divergent homologues. Our results showed that, in healthy fish, the BsCXCR transcripts was mainly distributed in the muscle and immune related organs, and that BsCXCR1a/1b proteins located in the cytomembrane, BsCXCR4a/4b/5/6 in the cytomembrane and perinuclear region, and BsCXCR3a1/3a2/7 in the cytomembrane, perinuclear region, and nuclear membrane, respectively. In skin injured fish, the transcripts of all BsCXCRs were transiently increased within one hour after injury, suggesting the involvement of BsCXCRs into the early inflammatory response to skin injury in the four-eyed sleeper. These results are valuable for understanding the evolutionary events of fish CXCR genes and provide insights into the roles of CXCR family in fish skin injury.

α-Lipoic Acid Exerts Its Antiviral Effect against Viral Hemorrhagic Septicemia Virus (VHSV) by Promoting Upregulation of Antiviral Genes and Suppressing VHSV-Induced Oxidative Stress.

Viral hemorrhagic septicemia virus (VHSV), belonging to the genus Novirhabdovirus, Rhabdoviridae family, is a causative agent of high mortality in fish and has caused significant losses to the aquaculture industry. Currently, no effective vaccines, Food and Drug Administration-approved inhibitors, or other therapeutic intervention options are available against VHSV. α-Lipoic Acid (LA), a potent antioxidant, has been proposed to have antiviral effects against different viruses. In this study, LA (CC50 = 472.6 µmol/L) was repurposed to exhibit antiviral activity against VHSV. In fathead minnow cells, LA significantly increased the cell viability post-VHSV infection (EC50 = 42.7 µmol/L), and exerted a dose-dependent inhibitory effect on VHSV induced-plaque, cytopathic effects, and VHSV glycoprotein expression. The time-of-addition assay suggested that the antiviral activity of LA occurred at viral replication stage. Survival assay revealed that LA could significantly upregulated the survival rate of VHSV-infected largemouth bass in both co-injection (38.095% vs. 1.887%, P < 0.01) and post-injection manner (38.813% vs. 8.696%, P < 0.01) compared with the control group. Additional comparative transcriptome and qRT-PCR analysis revealed LA treatment upregulated the expression of several antiviral genes, such as IRF7, Viperin, and ISG15. Moreover, LA treatment reduced VHSV-induced reactive oxygen species production in addition to Nrf2 and SOD1 expression. Taken together, these data demonstrated that LA suppressed VHSV replication by inducing antiviral genes expression and reducing VHSV-induced oxidative stress. These results suggest a new direction in the development of potential antiviral candidate drugs against VHSV infection.

MicroRNA expression profiling of sea perch brain cells reveals the roles of microRNAs in autophagy induced by RGNNV infection.

Nervous necrosis virus (NNV) is one of the most destructive fish viruses and affects more than 120 marine and freshwater teleost species. However, the pathogenesis of NNV has not been made clear. MicroRNAs (miRNAs) play important roles in the regulation of viral infection. To understand the roles and regulation patterns of miRNAs in NNV infection, high-throughput sequencing was carried out in Lateolabrax japonicus brain (LJB) cells with or without red-spotted grouper NNV (RGNNV) infection at 12 and 24 hr. Here, we identified 59 known and 61 novel differentially expressed miRNAs (DE miRNAs) between mock and RGNNV-infected LJB cells. KEGG pathway analysis showed that the target genes of DE miRNAs were significantly enriched in immune-related signalling pathways, such as autophagy, mitophagy and TGF-beta signalling pathways. The expression patterns of four DE miRNAs (lja-miR-145, lja-miR-182, lja-miR-183 and lja-miR-187) were verified by qRT-PCR both in vivo and in vitro. We found that lja-miR-145 promoted RGNNV proliferation, while lja-miR-183 suppressed RGNNV proliferation. Furthermore, lja-miR-145 facilitated RGNNV-induced autophagy activation, whereas lja-miR-183 repressed autophagy in LJB cells as measured by LC3B-II/I and p62 protein levels. All these results indicate the involvement of lja-miR-145 and lja-miR-183 in RGNNV-induced autophagy. In conclusion, this study provides evidence for the important roles of miRNAs in NNV infection and a basis for uncovering the molecular regulation mechanism of NNV-induced autophagy.

E3 Ubiquitin Ligase RNF114 Inhibits Innate Immune Response to Red-Spotted Grouper Nervous Necrosis Virus Infection in Sea Perch by Targeting MAVS and TRAF3 to Mediate Their Degradation.

RIG-I-like receptor (RLR)-mediated antiviral signaling is critical to trigger the immune response to virus infection; however, the antiviral responses are also tightly regulated to avoid uncontrolled production of type I IFN by various mechanisms, including ubiquitination. In this study, an E3 ubiquitin ligase ring finger protein 114 (RNF114) from sea perch (Lateolabrax japonicus) (LjRNF114) was identified as a suppressor of RLR signaling pathways during red-spotted grouper nervous necrosis virus (RGNNV) infection. RGNNV infection promoted the expression of LjRNF114. Overexpression of LjRNF114 enhanced RGNNV replication, whereas knockdown of LjRNF114 led to opposite effects. Type I IFN production induced by RGNNV was suppressed by LjRNF114, which is dependent on its ubiquitin ligase activity. Moreover, LjRNF114 inhibited IFN promoter activation induced by key signaling molecules in RLR signaling pathways. We observed the interactions between LjRNF114 and both sea perch mitochondrial antiviral signaling protein (MAVS) and TNFR-associated factor 3 (TRAF3). Domain mapping experiments indicated that the RING and ubiquitin interacting motif domains of LjRNF114 were required for its interaction with TRAF3 and MAVS. We found that LjRNF114 targeted MAVS and TRAF3 for K27- and K48-linked ubiquitination and degradation, resulting in the inhibition of IFN production. Taken together, our study reveals, to our knowledge, a novel mechanism that LjRNF114 targets and promotes K27- and K48-linked ubiquitination of MAVS and TRAF3 to negatively regulate the RLR signaling pathways, promoting viral infection.