Innate immune response of channel catfish Ictalurus punctatus mannose-binding lectin to channel catfish virus (CCV)

Effect of Agaricus bisporus Polysaccharides (ABPs) on anti-CCV immune response of channel catfish

Herein, the effects of Agaricus bisporus Polysaccharides (ABPs) on anti-channel catfish virus (CCV) infections to promote their application in channel catfish culture were explored. Transcriptome and metabolome analyses were conducted on the spleen of a CCV-infected channel catfish model fed with or without ABPs. CCV infections upregulated many immune and apoptosis-related genes, such as IL-6, IFN-α3, IFN-γ1, IL-26, Casp3, Casp8, and IL-10, and activated specific immunity mediated by B cells. However, after adding ABPs, the expression of inflammation-related genes decreased in CCV-infected channel catfish, and the inflammatory inhibitors NLRC3 were upregulated. Meanwhile, the expression of apoptosis-related genes was reduced, indicating that ABPs can more rapidly and strongly enhance the immunity of channel catfish to resist viral infection. Moreover, the metabonomic analysis showed that channel catfish had a high energy requirement during CCV infection, and ABPs could enhance the immune function of channel catfish. In conclusion, ABPs can enhance the antiviral ability of channel catfish by enhancing immune response and regulating inflammation. Thus, these findings provided new insights into the antiviral response effects of ABPs, which might support their application in aquaculture.

Genome-Wide Identification, Phylogeny, and Expression Profile of the Dmrt (Doublesex and Mab-3 Related Transcription Factor) Gene Family in Channel Catfish (Ictalurus punctatus)

The Dmrt (Doublesex and Mab-3 related transcription factor) gene family is a class of crucial transcription factors characterized by a conserved DM domain related to sex determination and differentiation, which has been systematically described in various teleost fish, but less in channel catfish (Ictalurus punctatus), an important global aquaculture species in the US and China. In this study, seven Dmrt genes from channel catfish genome were identified and analyzed using bioinformatics methods. Seven IpDmrt genes were distributed unevenly across five chromosomes. Synteny analysis revealed that Dmrt1, Dmrt2a, Dmrt2b, Dmrt3, Dmrt4, and Dmrt5 were relatively conserved in teleost fish. Tissue distribution analysis showed that IpDmrt1, IpDmrt2b, IpDmrt5, and IpDmrt6 exhibited sexually dimorphic expression patterns and, among them, IpDmrt1 and IpDmrt6 had high expression levels in the testes, while IpDmrt2b and IpDmrt5 had more significant expression levels in the ovaries than in other tissues. After 17β-estradiol treatment, IpDmrt2b and IpDmrt5 were significantly up regulated, while the expression of IpDmrt1 and IpDmrt6 was significantly repressed in XY channel catfish ovaries compared with XX channel catfish ovaries. The present study provides a comprehensive insight into the Dmrt gene family of channel catfish. The results suggest that IpDmrt1 and IpDmrt6 may play an important role in testis differentiation/development, while IpDmrt2b and IpDmrt5 are critical in ovary development in this species.

Electron microscopy reveals viral-like particles and mitochondrial degradation in scombrid puffy snout syndrome

Aquaculture is an increasingly important food resource, but its sustainability is often limited by disease. In Scombridae fishes, puffy snout syndrome (PSS) is a debilitating condition where tumor-like collagenous growths form around the eyes, nares, and mandibles which impair vision and feeding and frequently lead to mortality. While PSS is considered an infectious or metabolic disease, no disease agents or promoters have been identified. Here, we used electron microscopy (EM) to describe the cellular pathology and search for etiological agents of PSS in Pacific mackerel Scomber japonicus, the first use of this approach for PSS. We examined aquaculture specimens across a range of apparent PSS severity, comparing the results to both wild and aquaculture asymptomatic mackerel. EM imagery consistently revealed viral-like particles in PSS samples, as well as the uniform absence of bacteria, protists, fungi, and other multicellular parasites. In addition to viral-like particles, symptomatic fish had a higher mean percentage of swollen and disintegrating mitochondria than both asymptomatic aquaculture and wild mackerel. This suggests that degraded mitochondria may be related to PSS and could be important to further understanding the origin, promoters, and prevention of PSS. This study serves as a first step in identifying the etiological agents of PSS.

Antimicrobial activity of mannose binding lectin in grass carp (Ctenopharyngodon idella) in vivo and in vitro

Mannose-binding lectin (MBL) is a crucial pattern recognition receptor in the host innate immune system. Previously, we reported the biological function of Ctenopharyngodon idella MBL (CiMBL) in initiating the lectin pathway of the complement system. In the present study, we further explored its biological function including the agglutinating ability, binding capacity and protective role in vitro and in vivo. After Aeromonas hydrophila infection, western blot analysis revealed that the CiMBL were fluctuated and expressed in the serum and major immune-related tissues. The result of quantitative PCR (qPCR) showed that the recombinant CiMBL (rCiMBL) significantly inhibited the mRNA expression of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in liver, spleen and hepatic cells. Due to rCiMBL bound to d-mannose, d-galactose, d-glucose, N-acetyl-d-glucosamine (GlcNAc), lipopolysaccharide (LPS), peptidoglycan (PGN) and Agar in the presence of Ca²⁺, herein gram-positive (Staphylococcus aureus and Micrococcus luteus) and gram-negative (A. hydrophila and Vibrio anguillarum) bacteria were agglutinated by rCiMBL in a Ca²⁺-dependent manner. More importantly, rCiMBL enhanced the survival rate of grass carp following bacterial infection. Overall, the results provide an evidence that CiMBL can protect grass carp against A. hydrophila infection in aquaculture.

Molecular and functional characterisation of a mannose-binding lectin-like gene from Japanese sea bass (Lateolabrax japonicus)

Mannose-binding lectin (MBL) plays an important role in host immune responses against pathogens. LjMBL-like-1 was identified from Japanese sea bass (Lateolabrax japonicas), which has selectivity for galactose. Herein, this lectin might be better designated as galactose-binding lectin (LjGalBL-1). LjGalBL-1 transcripts were detected in all tested tissues, with highest expression in liver. Upon Vibrio harveyi infection, LjGalBL-1 mRNA expression was increased in major immune-related tissues, and protein levels in serum were also upregulated. Recombinant LjGalBL-1 (rLjGalBL-1) bound to monosaccharides and polysaccharides, and both rLjGalBL-1 and native LjGalBL-1 (nLjGalBL-1) agglutinated three Gram-positive bacteria (Staphylococcus aureus, Streptococcus iniae and Micrococcus luteus) and four Gram-negative bacteria (Aeromonas hydrophila, Edwardsiella tarda, Vibrio anguillarum and V. harveyi) in a Ca²⁺-dependent manner in vitro. Moreover, rLjGalBL-1 increased the survival rate of V. harveyi-infected fish and decreased bacterial load in liver, spleen, kidney and blood. Thus, LjGalBL-1 protects L. japonicas against V. harveyi infection.

Transcriptome sequencing of the gill and barbel of Southern catfish (Silurus meridionalis) revealed immune responses and novel rhamnose-binding lectins (RBLs)

Southern catfish (Silurus meridionalis) is an economically important species widely cultured in China. It is well known for its fast growth, strong resistance to diseases and euryphage. However, little is known about the mechanisms for its powerful immune systems. Our Fish-T1K project has finished its first phase of 200 fish transcriptomes, with sequencing of gills in most examined fishes. In this study, we performed transcriptome sequencing of the gill and the maxillary barbel of Southern catfish, with the latter as a control. High expression of immune-related transcripts were observed in these two tissues. We observed that genes in the T cell receptor signaling pathway had higher transcription values in the gill than in the barbel. In addition, eight new rhamnose-binding lectins (RBLs) were identified and their carbohydrate recognition domains (CRDs) were classified according to the eight conserved cysteine residues and two conserved motifs (-YGR- and -DPC-). This is the first transcriptome report by high-throughput sequencing of the Southern catfish. Our genomic data and discovery of novel RBLs in this project should be able to promote better understandings of the roles of gills in immune responses and disease prevention for further aquaculture.

Transcriptomic Profiles of Senegalese Sole Infected With Nervous Necrosis Virus Reassortants Presenting Different Degree of Virulence

Betanodaviruses [nervous necrosis virus (NNV)] are the causative agent of the viral encephalopathy and retinopathy, a disease that affects cultured Senegalese sole (Solea senegalensis). NNV reassortants, combining genomic segments from redspotted grouper nervous necrosis virus (RGNNV) and striped jack nervous necrosis virus (SJNNV) genotypes, have been previously isolated from several fish species. The wild-type reassortant wSs160.03, isolated from Senegalese sole, has been proven to be more virulent to sole than the parental genotypes (RGNNV and SJNNV), causing 100% mortality. Mutations at amino acids 247 (serine to alanine) and 270 (serine to asparagine) in the wSs160.03 capsid protein have allowed us to obtain a mutant reassortant (rSs160.03_247+270), which provokes a 40% mortality decrease. In this study, the RNA-Seq technology has been used to comparatively analyze Senegalese sole transcriptomes in two organs (head kidney and eye/brain) after infection with wild-type and mutant strains. A total of 633 genes were differentially expressed (DEGs) in animals infected with the wild-type isolate (with higher virulence), whereas 393 genes were differentially expressed in animals infected with the mutant strain (37.9% decrease in the number of DEGs). To study the biological functions of detected DEGs involved in NNV infection, a gene ontology (GO) enrichment analysis was performed. Different GO profiles were obtained in the following subclasses: (i) biological process; (ii) cellular component; and (iii) molecular function, for each viral strain tested. Immune response and proteolysis have been the predominant biological process after the infection with the wild-type isolate, whereas the infection with the mutant strain induces proteolysis in head kidney and inhibition of vasculogenesis in nervous tissue. Regarding the immune response, genes coding for proteins acting as mediators of type I IFN expression (DHX58, IRF3, IRF7) and IFN-stimulated genes (ISG15, Mx, PKR, Gig1, ISG12, IFI44, IFIT-1, to name a few) were upregulated in animals infected with the wild-type isolate, whereas no-differential expression of these genes was observed in samples inoculated with the mutant strain. The different transcriptomic profiles obtained could help to better understand the NNV pathogenesis in Senegalese sole, setting up the importance as virulence determinants of amino acids at positions 247 and 270 within the RNA2 segment.