Calreticulin functions in antimicrobial immunity of obscure puffer Takifugu obscurus.

Calreticulin (Crt) is a highly conserved and multi-functional protein with lectin-like properties and important immunological activities. In this study, a Crt homolog, namely, ToCrt, was cloned and characterized from the obscure puffer Takifugu obscurus with an open reading frame of 1278 bp encoding a putative protein of 425 amino acids. The deduced amino acid sequence of ToCrt consisted of three conserved structural domains: N-domain, P-domain, and C-terminal domain. In the phylogenetic tree, ToCrt formed a separate cluster with three Crts from other pufferfish species (Takifugu rubripes, Takifugu flavidus, and Takifugu bimaculatus). The mRNA transcript of ToCrt was ubiquitously expressed in all the examined tissues in a decreasing order: liver, spleen, kidney, gills, intestine, and heart. After Vibrio harveyi, Edwardsiella tarda, and Aeromonas hydrophila stimulations, the levels of ToCrt mRNA in the kidney and spleen were significantly upregulated compared with that in the control group. The recombinant calreticulin domain of ToCrt (rToCrt) could bind three Gram-negative bacteria (V. harveyi, E. tarda, and A. hydrophila) and polysaccharides from bacterial cell walls such as lipopolysaccharide and peptidoglycan. Meanwhile, rToCrt could agglutinate different kinds of microorganisms and exhibit antimicrobial activity. These results suggested that T. obscurus ToCrt could serve as an antimicrobial effector in the host immune response against invading microorganisms.

Comparative Metabolomics and Proteomics Reveal Vibrio parahaemolyticus Targets Hypoxia-Related Signaling Pathways of Takifugu obscurus.

Coronavirus disease 2019 (COVID-19) raises the issue of how hypoxia destroys normal physiological function and host immunity against pathogens. However, there are few or no comprehensive omics studies on this effect. From an evolutionary perspective, animals living in complex and changeable marine environments might develop signaling pathways to address bacterial threats under hypoxia. In this study, the ancient genomic model animal Takifugu obscurus and widespread Vibrio parahaemolyticus were utilized to study the effect. T. obscurus was challenged by V. parahaemolyticus or (and) exposed to hypoxia. The effects of hypoxia and infection were identified, and a theoretical model of the host critical signaling pathway in response to hypoxia and infection was defined by methods of comparative metabolomics and proteomics on the entire liver. The changing trends of some differential metabolites and proteins under hypoxia, infection or double stressors were consistent. The model includes transforming growth factor-ß1 (TGF-ß1), hypoxia-inducible factor-1α (HIF-1α), and epidermal growth factor (EGF) signaling pathways, and the consistent changing trends indicated that the host liver tended toward cell proliferation. Hypoxia and infection caused tissue damage and fibrosis in the portal area of the liver, which may be related to TGF-ß1 signal transduction. We propose that LRG (leucine-rich alpha-2-glycoprotein) is widely involved in the transition of the TGF-ß1/Smad signaling pathway in response to hypoxia and pathogenic infection in vertebrates as a conserved molecule.

Expression profile of kalliklectin, a soluble-type mannose receptor, during embryogenesis and early larval development in fugu (Takifugu rubripes).

Kalliklectin is a unique fish-specific lectin, whose sequence is similar to the heavy chain of mammalian plasma kallikrein and coagulation factor XI. In this study, we aimed to evaluate dynamic expression profiles of the lectin gene, during early developmental stages, in fugu, Takifugu rubripes. Reverse transcription-polymerase chain reaction (RT-PCR) showed that the kalliklectin gene was not expressed until 14 h post-fertilization (hpf), while the mRNA was detected after 30 hpf. In real-time quantitative PCR (qPCR), the gene was first expressed at 10.5 hpf; then, the expression level increased with a peak at 30 hpf and then gradually decreased. On the other hand, western blotting with specific antibody detected the lectin protein at all tested stages, including the unfertilized egg, which suggests that the lectin detected in the early stages was a maternal factor. Immunohistochemistry demonstrated that kalliklectin was localized at the basement membranes of the newly hatched larvae, while the lectin was widely detected in epidermal cells in larva at 5 dph. A 40-kDa lectin was partially purified from unfertilized eggs using mannose-affinity chromatography, and the lectin was determined as kalliklectin by liquid chromatography with quadrupole time-of-flight tandem mass spectrometry (LC/Q-TOF-MS) analysis, which indicated that the lectin is functional in the eggs. The egg lectin can bind to Gram-positive bacterial pathogens of fish, such as Lactococcus garvieae and Streptococcus iniae. We conclude that fugu kalliklectin might be an important immunocomponent, transferred from mother to offspring.

Quantitative proteomic analysis in serum of Takifugu rubripes infected with Cryptocaryon irritans.

Cryptocaryon irritans can cause cryptocaryonosis (white spot disease) in marine fish but the pathogenesis of the disease is unclear. In this work, we used high-throughput proteomics to identify differentially expressed proteins in the serum of Takifugu rubripes challenged with C. irritans. By using quantitative proteomic assays combined with Tandem Mass Tag-labeled quantitative proteomic analysis, we identified a total of 2088 differentially abundant proteins (1706 proteins were quantified, p < 0.05, fold-change threshold ≥ 2), including 21 up-regulated and 44 down-regulated. Combined with STRING-based functional analysis, we ultimately obtained eight proteins including glucokinase-like, integrin beta-1-like isoform X2, H4, H2A.V, histone H1-like, histone H2AX-like, histone H2B 1/2-like and myosin-9 isoform X1, which could be considered as potential biomarkers for T. rubripes immune responses. Eight proteins that were selected to validate significant differentially expressed genes at the proteomic level were consistent with qPCR at the transcriptomic level. The proteins identified in our work may serve as candidates for elucidating the molecular mechanism of cryptocaryonosis in T. rubripes. Our collective findings could provide new insights into searching for disease-specific targets and biomarkers, which may be effective indicators of C. irritans infection in T. rubripes.

A live attenuated Vibrio anguillarum vaccine induces efficient immunoprotection in Tiger puffer (Takifugu rubripes).

Tiger puffer (Takifugu rubripes) is becoming an economic promising aquaculture species in China. However, the development of Tiger puffer breeding industry is restricted by some serious aquatic disease such as vibriosis. An effective live attenuated vaccine MVAV6203 was developed in our previous studies by curing the virulence plasmid pEIB1 and unmarked inframe-deletion of the aroC gene from the virulent V. anguillarum. Here, we evaluated whether this live vaccine was suitable for Tiger puffer against disease caused by Vibrio genus. The live vaccine show virulence attenuation in both juvenile and adult fish vaccinated with either a single or high dose (50-fold single dose). In addition, administration of the live vaccine shew limited growth in fish and did not affect fish body weight significantly, with no adverse impact on growth between vaccinated and saline control fish. Furthermore, increased expression of cytokines involved in pro-inflammatory (IL-1ß, TNFα and IL-6), cell-mediated immunity inducing (IL-12p35, IL-12p40 and IL-18), antiviral/intracellular pathogen killing (I-IFN-1, IFN-γ and Mx), peripheral T cell expansion and survival controlling (IL-2, IL-7 and IL-15) and antigen processing maker and anti-inflammatory (MHC I and IL-10) were elicited significantly after the vaccination. These cellular responses correlate with protection against virulent strain challenge and high RPS of 90.67% and 80.31% in juvenile and adult fish were obtained, respectively. These data indicated for the first time that the live attenuated V. anguillarum vaccine is suitably applied for the development of an effective and safe vaccine for prevention of vibriosis in Tiger puffer aquaculture industry.

Accumulation of hydroxyl lipids and 4-hydroxy-2-hexenal in live fish infected with fish diseases.

Hydroxy lipids (L-OH) and 4-hydroxy-2-hexenal (HHE) levels as well as other parameters such as lipid level, lipid class, fatty acid composition, and other aldehydes levels in the liver of diseased fish were investigated. Although significant differences in lipid level, lipid class, fatty acid composition, and other aldehyde levels were not always observed between normal and diseased fish, L-OH and HHE levels were significantly higher in the liver of the diseased fish than in that of the normal fish cultured with the same feeds under the same conditions. In the liver of puffer fish (Fugu rubripes) infected with Trichodina, L-OH and HHE levels significantly increased from 25.29±5.04 to 47.70 ± 5.27 nmol/mg lipid and from 299.79±25.25 to 1,184.40±60.27 nmol/g tissue, respectively. When the levels of HHE and other aldehydes in the liver of the normal and diseased puffer fish were plotted, a linear relationship with a high correlation coefficient was observed between HHE and propanal (r2=0.9447). Increased L-OH and HHE levels in the liver of the diseased fish and a high correlation between HHE and propanal in the liver of the normal and diseased fish were also observed in flat fish (Paralichthys olivaceus) infected with streptococcus, yellowtail (Seriola quinqueradiata) infected with jaundice, and amberjack (S. purpurascens) infected with Photobacterium damselae subsp. piscicida.

Serum GlcNAc-binding IgM of fugu (Takifugu rubripes) suppresses the growth of fish pathogenic bacteria: a novel function of teleost antibody.

N-acetyl-d-glucosamine (GlcNAc) is one of the components of peptidoglycan, a biopolymer in the bacterial cell wall. We purified a novel GlcNAc-binding protein, designated as fGBP-78, from sera of fugu (Takifugu rubripes). The fGBP-78 is a heteromer of 78- and 25-kDa subunits. Moreover, fGBP-78 exerted remarkable inhibitory effects on the growth of both Gram-positive and Gram-negative bacteria, including ones virulent for marine fish species as well as non-pathogenic Escherichia coli. These results suggest that fGBP-78 contributes to bacterial clearance in fugu. Furthermore, the nanoLC-MS/MS and Western blotting analyses reveal that the 78-kDa subunit is the fugu IgM heavy chain. In addition, the molecular mass of the other subunit (25 kDa) was equal to that of the Ig light chain. Overall, results indicate that fGBP-78 is an IgM molecule presumably acts as a natural antibody. This paper reports a novel function of teleost IgM as a significant suppresser against bacterial growth.

Isolation of a Lysinibacillus fusiformis strain with tetrodotoxin-producing ability from puffer fish Fugu obscurus and the characterization of this strain.

Six dominant strains were isolated from the livers of the puffer fish Fugu obscurus and were screened for their TTX production-ability. Electrospray ionization-mass spectrometry (ESI-MS) analyses revealed that strain B-1 produced TTX and related substances; mouse bioassay revealed that 23.9 mouse units (MU) of toxins were present in 200ml of broth medium. On the basis of the physiological and biochemical characteristics of this strain and the results of 16S rRNA analysis, strain B-1 was identified as Lysinibacillus fusiformis.

Toxicity and distribution of tetrodotoxin-producing bacteria in puffer fish Fugu rubripes collected from the Bohai Sea of China.

To investigate the relationship between the toxicity of puffer fish and the distribution of tetrodotoxin-producing bacteria in puffer fish Fugu rubripes collected from the Bohai Sea of China, bacteria were isolated from each organ (ovaries, livers, intestines and gallbladders) and screened for tetrodotoxin (TTX) production. 20 out of 36 isolated strains were found to produce TTX in vitro. In the organs of ovaries and livers whose toxicity is more potent than other organs, the number and toxicity of TTX-producing strains was greater than that of others. Most TTX-producing bacterial strains were identified as Bacillus spp. (19 strains) and Actinomycete spp. (1 strain) based on the morphological observation, physiological and biochemical characteristics and G+C content of DNA. The purified toxin was identified to be TTX by high performance liquid chromatography assay, thin-layer chromatography assay and electrospray ionization mass spectrometry analysis. Our results suggested that TTX-producing bacteria are closely related to the toxification of the puffer fish. More research is needed to elucidate the mechanism of TTX synthesis and the role of TTX in bacteria.

A new tetrodotoxin-producing actinomycete, Nocardiopsis dassonvillei, isolated from the ovaries of puffer fish Fugu rubripes.

Three puffer fishes, Fugu rubripes, collected from the Bohai Sea of China were examined for tetrodotoxin-producing microorganisms. An actinomycete isolated from the ovaries of the puffer fishes was found to produce tetrodotoxin. After being cultured at 28 degrees C for 7 days, cells were harvested by centrifuge and disrupted by ultrasonication. The toxin was purified from the cell lyzate by ultrafiltration, active charcoal column, Bio-gel-p2 and ion exchange column chromatography. Mouse neuroblastoma cell culture, thin-layer chromatography, fluorimetric spectrophotometry, UV-spectrophotometry and electrospray ionization mass spectrometry, together with mouse bioassay demonstrated that the isolated strain produced tetrodotoxin and related toxin during cultivation. Based on morphological, physiological, biochemical characteristics and 16S rDNA alignment, this strain was identified as Nocardiopsis dassonvillei. Our findings suggested that N. dassonvillei in the ovaries was closely related to the toxification of the puffer fish.

[Microecological distribution of toxin-producing bacteria in Fug rubripes in Bohai Sea and biological characteristics of B3B].

The study showed that toxin-producing bacteria were commonly existed in each part of Fugu rubripes body. 19 strains of high poisonous bacteria were isolated from its ovary, liver and other tissues, among which, strain B3B was identified as genus Bacillus based on its physiological and biochemical characteristics and 16SrDNA sequence, and could produce tetrodotoxin through mouse test, thinner chromatography, and mass spectrography.