Pufferfish Saxitoxin and Tetrodotoxin Binding Protein (PSTBP) Analogues in the Blood Plasma of the Pufferfish Arothron nigropunctatus, A. hispidus, A. manilensis, and Chelonodon patoca

Tetrodotoxin/Saxitoxin Accumulation Profile in the Euryhaline Marine Pufferfish Chelonodontops patoca

Marine Takifugu pufferfish, which naturally possess tetrodotoxins (TTXs), selectively take up and accumulate TTXs, whereas freshwater Pao pufferfish, which naturally possess saxitoxins (STXs), selectively take up and accumulate STXs. To further clarify the TTXs/STXs selectivity in pufferfish, we conducted a TTX/STX administration experiment using Chelonodontops patoca, a euryhaline marine pufferfish possessing both TTXs and STXs. Forty nontoxic cultured individuals of C. patoca were divided into a seawater group (SW, acclimated/reared at 33‱ salinity; n = 20) and a brackish water group (BW, acclimated/reared at 8‱ salinity; n = 20). An aqueous TTX/STX mixture was intrarectally administered (both at 7.5 nmol/fish), and five individuals/group were analyzed after 1-48 h. Instrumental toxin analyses revealed that both TTX and STX were taken up, transferred, and retained, but more STX than TTX was retained in both groups. TTX gradually decreased and eventually became almost undetectable in the intestinal tissue, while STX was retained at ~5-10% of the dose level, and only STX showed transient transfer in the liver. The BW group showed a faster decrease/disappearance of TTX, greater STX retention in the intestine, and greater STX transient transfer to the liver. Thus, C. patoca appears to more easily accumulate STXs than TTXs, especially under hypoosmotic conditions.

Binding and sequestration of poison frog alkaloids by a plasma globulin

Alkaloids are important bioactive molecules throughout the natural world, and in many animals they serve as a source of chemical defense against predation. Dendrobatid poison frogs bioaccumulate alkaloids from their diet to make themselves toxic or unpalatable to predators. Despite the proposed roles of plasma proteins as mediators of alkaloid trafficking and bioavailability, the responsible proteins have not been identified. We use chemical approaches to show that a ~50 kDa plasma protein is the principal alkaloid-binding molecule in blood of poison frogs. Proteomic and biochemical studies establish this plasma protein to be a liver-derived alkaloid-binding globulin (ABG) that is a member of the serine-protease inhibitor (serpin) family. In addition to alkaloid-binding activity, ABG sequesters and regulates the bioavailability of 'free' plasma alkaloids in vitro. Unexpectedly, ABG is not related to saxiphilin, albumin, or other known vitamin carriers, but instead exhibits sequence and structural homology to mammalian hormone carriers and amphibian biliverdin-binding proteins. ABG represents a new small molecule binding functionality in serpin proteins, a novel mechanism of plasma alkaloid transport in poison frogs, and more broadly points toward serpins acting as tunable scaffolds for small molecule binding and transport across different organisms.

Wheat germ agglutinin affinity chromatography enrichment and glyco-proteomic characterization of tetrodotoxin-binding proteins from the plasma of cultured tiger pufferfish (Takifugu rubripes)

Efficient enrichment of tetrodotoxin (TTX)-binding proteins from the plasma of cultured tiger pufferfish (Takifugu rubripes) was achieved by ammonium sulfate fractionation and wheat germ agglutinin (WGA) affinity chromatography. The enrichment efficiency was validated by ultrafiltration-LC/MS-based TTX-binding assay and proteomics. Major proteins in the WGA-bound fraction were identified as isoform X1 (125 kDa) and X2 variants (88 and 79 kDa) derived from pufferfish saxitoxin and tetrodotoxin-binding protein (PSTBP) 1-like gene (LOC101075943). The 125-kDa X1 protein was found to be a novel member of the lipocalin family, having three tandemly repeated domains. X2 variants, X2α and X2β, were estimated to have two domains, and X2β is structurally related to Takifugu pardalis PSTBP2 in their domain type and arrangement. Among 11 potential N-glycosylation sites in the X2 precursor, 5 N-glycosylated Asn residues (N55, N89, N244, N308, and N449) were empirically determined. Structural relationships among PSTBP homologs and complexity of their proteoforms are discussed.

Establishment and characterization of the ovary cell line derived from two-spot puffer Takifugu bimaculatus and its application for gene editing and marine toxicology

Takifugu bimaculatus is a marine fish with high nutritional value. Its ovary contains tetrodotoxin (TTX) which is a severe neurotoxin that limits its edible value of it. To understand the mechanism of oogenesis and production of TTX in T. bimaculatus, an ovarian cell line named TBO from an adolescent ovary was established. TBO was composed of fibroblast-like cells that expressed the ovarian follicle cells marker gene Foxl2 and highly expressed TTX binding protein 2 (PSTBP2) but did not express the germ cells marker gene Vasa. Therefore, TBO seems to be mainly composed of follicle cells and possibly a small percentage of oocytes. Electroporation was used to successfully transfect the pEGFP-N1 and pNanog-N1 vectors into the TBO cell line with a high transfection efficiency. The morphological changes and survival rates of the exposed cells proved that this cell line was effective for exposure to conotoxins (CTXs), another group of toxins related to food safety. Furthermore, PSTBP2 was knocked out in TBO using CRISPR/Cas9 technology, showing that sgRNA2 could mutate PSTBP2. The results suggested that TBO will be more convenient, efficient, and rapid for reproduction and toxicology investigation, and gene editing. This study laid the groundwork for future research into the fish gonadal cell culture and food-related marine toxins. In conclusion, a cell line has been generated from T. bimaculatus, which might represent a valuable model for fish studies in the fields of toxicology and gene editing.

Transcriptomic analysis reveals the genes involved in tetrodotoxin (TTX) accumulation, translocation, and detoxification in the pufferfish Takifugu rubripes

Tetrodotoxin (TTX) is a potent marine neurotoxin that exists in a variety of aquatic and terrestrial organisms. Pufferfish in different habitats show great variation in their TTX contents. Exploring the genes involved in TTX metabolism could contribute to our understanding of the molecular mechanisms underlying TTX accumulation, translocation, and detoxification in pufferfish. In this study, transcriptomic analysis was used to identify the functional genes related to TTX metabolism in the blood, liver, and muscle of the toxic and non-toxic tiger puffer (Takifugu rubripes). A total of 6101 differentially expressed genes (DEGs) were obtained after transcriptomic analysis; of these, 2401 were identified in the blood, 2262 in the liver, and 1438 in the muscle. After enrichment analysis, fourteen genes encoding glutathione S-transferases (GSTs), glutathione peroxidase (GPx), thioredoxins (TXNs), superoxide dismutase (SOD), ATP-binding cassettes (ABCs), apolipoproteins (APOs), inhibitors of apoptosis protein (IAP), and solute carrier (SLC), which are mainly antioxidant enzymes, membrane transporters, or anti-apoptotic factors, were revealed in the blood. Thirty-six genes encoding SLCs, ABCs, long-chain-fatty-acid-CoA ligases (ACSLs), interleukin 6 cytokine family signal transducer (IL6ST), endoplasmic reticulum (ER), and heat shock protein family A (Hsp70) were involved in transmembrane transporter activity and innate immune response. Notably, a large number of slc genes were found to play critical and diverse roles in TTX accumulation and translocation in the liver of T. rubripes. Nine genes from the slc, hsp70, complement C5 (c5), acsl, er, and serpin peptidase inhibitor (serpin) gene families were found to participate in the regulation of protein processing and anti-apoptosis. These results reflect the diverse functions of genes closely related to TTX accumulation, translocation, and detoxification in T. rubripes.

Proteomic analysis of carp seminal plasma provides insights into the immune response to bacterial infection of the male reproductive system

Aeromonas salmonicida is recognized as a significant bacterial pathogen in ulcerative disease of cyprinid fish. However, the mechanism of immunity to these bacteria in common carp is still not well understood, especially the immune regulation in the gonad to bacterial infection. The aims of our study were to analyze changes in the seminal plasma proteome following A. salmonicida infection in carp males. The observed pathological changes in the tissue (liver, spleen, kidney and testis) morphology and upregulation of immune-related genes (tnfa2, il6a) confirmed the successful infection challenge. Using mass spectrometry-based label-free quantitative proteomics, we identified 1402 seminal plasma proteins, and 44 proteins (20 up- and 24 downregulated) were found to be differentially abundant between infected and control males. Most differentially abundant proteins were involved in the immune response mechanisms, such as acute phase response, complement activation and coagulation, inflammation, lipid metabolism, cell-cell and cell-matrix adhesion, creatine-phosphate biosynthesis and germ cell-Sertoli cell junction signaling. Bacterial infection also caused profound changes in expression of selected genes in the testis and hematopoietic organs, which contributed to changes in seminal proteins. The altered seminal proteins and bacterial proteins in seminal plasma may serve as valuable markers of infection in the testis.

Tetrodotoxins in the flatworm Planocera multitentaculata

The marine polyclad flatworm Planocera multitentaculata is known to possess high levels of tetrodotoxin (TTX), but the presence of TTX analogues in the species has been unexplored. In this study, TTX and several analogues such as 5,6,11-trideoxyTTX, monodeoxyTTXs, dideoxyTTXs, and 11-norTTX-6(S)-ol were identified in three adults and egg plates of P. multitentaculata using high resolution liquid chromatography-mass spectrometry (HR-LC/MS) for the first time.

Tetrodotoxin and analogues in two local pufferfish species from Inhaca Island - South of Mozambique: First report in the Mozambican coast

Tetrodotoxins (TTXs) were investigated in two local pufferfish species, Diodon hystrix and Arothron hispidus, from Mozambican coast. TTX and analogues 4-epiTTX, 4,9-anhydroTTX, 11-deoxyTTX, and 11-norTTX-6-(R/S)-ol were found in both species and high level of TTX was found in A. hispidus (9522.0 μg TTX kg^-1) than in D. hystrix (350.9 μg TTX kg^-1). The distribution of TTX and their analogues in A. hispidus was intestine > liver > skin ≫ muscle > gonads. This is the first report of TTXs in Mozambican coast.

The road not taken: Evolution of tetrodotoxin resistance in the Sierra garter snake (Thamnophis couchii) by a path less traveled

The repeated evolution of tetrodotoxin (TTX) resistance provides a model for testing hypotheses about the mechanisms of convergent evolution. This poison is broadly employed as a potent antipredator defense, blocking voltage-gated sodium channels (Na_v ) in muscles and nerves, paralyzing and sometimes killing predators. Resistance in taxa bearing this neurotoxin and a few predators appears to come from convergent replacements in specific Na_v residues that interact with TTX. This stereotyped genetic response suggests molecular and phenotypic evolution may be constrained and predictable. Here, we investigate the extent of mechanistic convergence in garter snakes (Thamnophis) that prey on TTX-bearing newts (Taricha) by examining the physiological and genetic basis of TTX resistance in the Sierra garter snake (Th. couchii). We characterize variation in this predatory adaptation across populations at several biological scales: whole-animal TTX resistance; skeletal muscle resistance, functional genetic variation in three Na_v encoding loci; and levels of gene expression for one of these loci. We found Th. couchii possess extensive geographic variation in resistance at the whole-animal and skeletal muscle levels. As in other Thamnophis, resistance at both levels is highly correlated, suggesting convergence across the biological levels linking organism to organ. However, Th. couchii shows no functional variation in Na_v loci among populations or difference in candidate gene expression. Local variation in TTX resistance in Th. couchii cannot be explained by the same relationship between genotype and phenotype seen in other taxa. Thus, historical contingencies may lead different species of Thamnophis down alternative routes to local adaptation.

Molecular Characterization of a New Tetrodotoxin-Binding Protein, Peroxiredoxin-1, from Takifugu bimaculatus

Pufferfish are considered a culinary delicacy but require careful preparation to avoid ingestion of the highly toxic tetrodotoxin (TTX), which accumulates in certain tissues. In this study, the tissue distribution of peroxiredoxin-1 from Takifugu bimaculatus was investigated. The peroxiredoxin-1 protein was obtained by in vitro recombinant expression and purification. The recombinant protein had a strong ability to scavenge hydroxyl radicals, protect superhelical DNA plasmids from oxidative damage, and protect L929 cells from H₂O₂ toxicity through in vitro antioxidant activity. In addition, we verified its ability to bind to tetrodotoxin using surface plasmon resonance techniques. Further, recombinant proteins were found to facilitate the entry of tetrodotoxin into cells. Through these analyses, we identified, for the first time, peroxiredoxin-1 protein from Takifugu bimaculatus as a potential novel tetrodotoxin-binding protein. Our findings provide a basis for further exploration of the application of peroxiredoxin-1 protein and the molecular mechanisms of tetrodotoxin enrichment in pufferfish.

Local Differences in the Toxin Amount and Composition of Tetrodotoxin and Related Compounds in Pufferfish (Chelonodon patoca) and Toxic Goby (Yongeichthys criniger) Juveniles

Tetrodotoxin (TTX)-bearing fish ingest TTX from their preys through the food chain and accumulate TTX in their bodies. Although a wide variety of TTX-bearing organisms have been reported, the missing link in the TTX supply chain has not been elucidated completely. Here, we investigated the composition of TTX and 5,6,11-trideoxyTTX in juveniles of the pufferfish, Chelonodon patoca, and toxic goby, Yongeichthys criniger, using LC–MS/MS, to resolve the missing link in the TTX supply chain. The TTX concentration varied among samples from different localities, sampling periods and fish species. In the samples from the same locality, the TTX concentration was significantly higher in the toxic goby juveniles than in the pufferfish juveniles. The concentration of TTX in all the pufferfish juveniles was significantly higher than that of 5,6,11-trideoxyTTX, whereas the compositional ratio of TTX and 5,6,11-trideoxyTTX in the goby was different among sampling localities. However, the TTX/5,6,11-trideoxyTTX ratio in the goby was not different among samples collected from the same locality at different periods. Based on a species-specific PCR, the detection rate of the toxic flatworm (Planocera multitentaculata)-specific sequence (cytochrome c oxidase subunit I) also varied between the intestinal contents of the pufferfish and toxic goby collected at different localities and periods. These results suggest that although the larvae of the toxic flatworm are likely to be responsible for the toxification of the pufferfish and toxic goby juveniles by TTX, these fish juveniles are also likely to feed on other TTX-bearing organisms depending on their habitat, and they also possess different accumulation mechanisms of TTX and 5,6,11-trideoxyTTX.

Tetrodotoxin Retention in the Toxic Goby Yongeichthys criniger

To investigate tetrodotoxin (TTX) retention by the toxic goby Yongeichthys criniger, rearing experiments feeding nontoxic diets were conducted using 12 (Group I) and 17 (Group II) specimens collected from a natural environment. The specimens were reared in an aquarium with aeration and fed a diet lacking TTX for 60 days. Specimens were removed at 0, 20, 40, and 60 days (Group I) or 0, 30, and 60 days (Group II) after initiation of rearing. Liquid chromatography/mass spectrometry and liquid chromatography-tandem mass spectrometry revealed that whole-body concentrations and amounts of TTX decreased with increasing rearing duration in Group I. There were similar decreases in Group II, but the trend differed among tissues; the concentrations and amounts of TTX in the skin exhibited the greatest decreases. The results imply that Y. criniger has low TTX retention ability.

Proteomic analysis of pikeperch seminal plasma provides novel insight into the testicular development of domesticated fish stocks

Control of the reproduction of domesticated stocks is considered a prerequisite for aquaculture development of pikeperch. However, knowledge about the physiology of the captive pikeperch male reproductive system and the biology of semen is very limited, especially regarding protein characteristics. The aims of our study were to characterize pikeperch sperm quantity and quality parameters and to analyze changes in the proteome of the same males spawned for the first and second times. Moreover, attempts were made to generate the first proteomic library of seminal plasma proteins. Semen collected during the first spawning season was characterized by lower sperm concentration and volume than for the second season. Using mass spectrometry-based label-free quantitative proteomics, we identified 850 proteins in the seminal plasma of pikeperch from both spawning seasons, and 65 seminal proteins were found to be differentially abundant between the first and second spawning seasons. The majority of differentially abundant proteins were involved in stress and immune responses, developmental processes, cofactor metabolic processes, proteolysis, cellular oxidant detoxification and organization of the extracellular matrix (ECM). In addition, several proteins unique to pikeperch seminal plasma were identified, including antifreeze proteins, hibernation-specific plasma proteins, lectins and vitellogenin. In summary, our results indicate that males that spawned for the first time were characterized by incompletely mature gonads and the expression of proteins associated with the early phase of spermatogenesis and ECM organization. On the other hand, males that spawned for the second time exhibited advanced gonadal maturation and expression of proteins related to the late stage of spermatogenesis and sperm maturation, including regulation of reactive oxygen species generation, bicarbonate production, sperm elongation and separation. The identification of a large number of seminal plasma proteins provides a valuable resource for understanding the functions of seminal plasma and the molecular mechanisms involved in testicular development and maturation in domesticated fish, which is a prerequisite for better control of reproduction in captivity.

Production of a tributyltin-binding protein 2 knockout mutant strain of Japanese medaka, Oryzias latipes

Tributyltin-binding proteins (TBT-bps), members of the lipocalin family, bind TBT in fish blood and are presumed to contribute to detoxification of TBT. Recent studies have shown that many fish species have TBT-bp genes, and that these genes are induced by stresses such as exposure to chemicals or fish pathogenic bacteria. However, the function of TBT-bps, and the mechanisms of their induction and detoxification activity are still unclear. Here, towards elucidating the functions of TBT-bp2, we produced a TBT-bp2 knockout (TBT-bp2^-/-) strain of Japanese medaka, Oryzias latipes, by using the CRISPR/Cas9 system. Gene expression of the mutated TBT-bp2 was reduced, and the cDNA sequencing and predicted protein structure suggested possible loss of function. However, the fish could be grown under normal conditions. Exposure of the TBT-bp2^-/- strain of medaka to various stresses in future experiments is expected to contribute to our understanding of this novel detoxification system in aquatic organisms.

Phylogeny and Toxin Profile of Freshwater Pufferfish (Genus Pao) Collected from 2 Different Regions in Cambodia

The species classification of Cambodian freshwater pufferfish is incomplete and confusing, and scientific information on their toxicity and toxin profile is limited. In the present study, to accumulate information on the phylogeny and toxin profile of freshwater pufferfish, and to contribute to food safety in Cambodia, we conducted simultaneous genetic-based phylogenetic and toxin analyses using freshwater pufferfish individuals collected from Phnom Penh and Kratie (designated PNH and KTI, respectively). Phylogenetic analysis of partial sequences of three mitochondrial genes (cytochrome b, 16S rRNA, and cytochrome c oxidase subunit I) determined for each fish revealed that PNH and KTI are different species in the genus Pao (designated Pao sp. A and Pao sp. B, respectively). A partial sequence of the nuclear tributyltin-binding protein type 2 (TBT-bp2) gene differentiated the species at the amino acid level. Instrumental analysis of the toxin profile revealed that both Pao sp. A and Pao sp. B possess saxitoxins (STXs), comprising STX as the main component. In Pao sp. A, the toxin concentration in each tissue was extremely high, far exceeding the regulatory limit for STXs set by the Codex Committee, whereas in Pao sp. B, only the skin contained high toxin concentrations. The difference in the STX accumulation ability between the two species with different TBT-bp2 sequences suggests that TBT-bp2 is involved in STX accumulation in freshwater pufferfish.

The chemistry and biology of guanidine secondary metabolites

Covering: 2017-2019Guanidine natural products isolated from microorganisms, marine invertebrates and terrestrial plants, amphibians and spiders, represented by non-ribosomal peptides, guanidine-bearing polyketides, alkaloids, terpenoids and shikimic acid derived, are the subject of this review. The topics include the discovery of new metabolites, total synthesis of natural guanidine compounds, biological activity and mechanism-of-action, biosynthesis and ecological functions.

Establishment of a Japanese medaka (Oryzias latipes) transgenic line expressing Takifugu rubripes pufferfish saxitoxin and tetrodotoxin binding protein 1, and evaluation of tributyltin toxicity via in ovo nanoinjection

Pufferfish saxitoxin and tetrodotoxin binding proteins (PSTBPs) play an important role in the toxification of certain species of pufferfish. Recombinant Takifugu rubripes PSTBP1 (rTrub.PSTBP1) is reported to bind to tributyltin, and so it has been suggested that rTrub.PSTBP1 may reduce the toxicity of tributyltin. However, the role of PSTBP1 in vivo remains to be elucidated. Here, we established a transgenic medaka line showing whole-body Renilla reniformis green fluorescent protein and Trub.PSTBP1 expression, as confirmed by real-time polymerase chain reaction and mRNA-Seq analysis. mRNA-Seq analysis also showed that cytochrome P450 superfamily genes and the gene encoding ATP-binding cassette sub-family G member 2 were highly expressed in the transgenic medaka. Using embryos of the transgenic medaka line, we conducted an in ovo nanoinjection test to examine the effect of Trub.PSTBP1 in vivo, and obtained data suggesting that Trub.PSTBP1 expression may have reduced the toxicity of tributyltin in our transgenic medaka line. Our findings will be useful for future functional analyses of Trub.PSTBP1.

Co-Occurrence of Tetrodotoxin and Saxitoxins and Their Intra-Body Distribution in the Pufferfish Canthigaster valentini

Pufferfish of the family Tetraodontidae possess tetrodotoxin (TTX) and/or saxitoxins (STXs), but the toxin ratio differs, depending on the genus or species. In the present study, to clarify the distribution profile of TTX and STXs in Tetraodontidae, we investigated the composition and intra-body distribution of the toxins in Canthigaster valentini. C. valentini specimens (four male and six female) were collected from Amami-Oshima Island, Kagoshima Prefecture, Japan, and the toxins were extracted from the muscle, liver, intestine, gallbladder, gonads, and skin. Analysis of the extracts for TTX by liquid chromatography tandem mass spectrometry and of STXs by high-performance liquid chromatography with post-column fluorescence derivatization revealed TTX, as well as a large amount of STXs, with neoSTX as the main component and dicarbamoylSTX and STX itself as minor components, in the skin and ovary. The toxins were also detected in the other tissues, but in much lower amounts than in the skin and ovary. The TTX/STX ratio varied greatly, depending on the tissue, but TTX was the major toxin component in the whole body, and STXs accounted for 25% and 13% of the total toxin amount in males and females, respectively. Like the marine pufferfish of the genus Arothron, C. valentini should be considered a pufferfish with considerable amounts of both TTX and STXs present simultaneously.

New tetrodotoxin analogs in Brazilian pufferfishes tissues and microbiome

While tetrodotoxin (TTX) is commonly found in pufferfish tissues, it is unclear if bacterial symbionts isolated from pufferfish tissues can produce TTX. In this investigation, UPLC qTOF-MS/MS analysis of tissue extracts obtained from Sphoeroides spengleri and Canthigaster figuereidoi identified TTX in their composition, indicating their consumption is unsafe. UPLC qTOF-MS/MS analysis coupled with Molecular Networking indicated new TTX analogs (methyl-TTX, TTX-acetate, hydroxypropyl-TTX and glycerol-TTX). Bacterial extracts from sixteen strains revealed a compound with a [M+H]⁺ ion at m/z 320.1088, identical to TTX. However, TTX itself was not detected in these cultures by UPLC-MS/MS. Neurotoxicity of Vibrio A665 purified fraction 2 (with precursor [M+H]⁺ ion at m/z 320.1088) was significant in human neural stem cells (hNSCs), but the Na_v blockage activity was not confirmed by the veratridine/ouabain essays, indicating a possible difference in the mechanism of action between the bacterium A665 purified fraction 2 and TTX. Vibrios symbionts of pufferfish point out involving in the production of TTX precursors.

Contrasting Toxin Selectivity between the Marine Pufferfish Takifugu pardalis and the Freshwater Pufferfish Pao suvattii

To clarify the differences in toxin selectivity between marine and freshwater pufferfish, we conducted experiments in artificially reared nontoxic specimens of Takifugu pardalis (marine) and Pao suvattii (freshwater) using tetrodotoxin (TTX) and paralytic shellfish poison (PSP; decarbamoylsaxitoxin (dcSTX) or saxitoxin (STX)). T. pardalis specimens were administered feed homogenate containing TTX or dcSTX (dose of toxin, 55.2 nmol/fish) and P. suvattii specimens were administered feed homogenate containing TTX + STX (dose of each toxin, 19.2 nmol/fish) by oral gavage. The toxin content in the intestine, muscle, skin, liver, and gonads was quantified after 24 and 48 or 72 h. In T. pardalis, TTX administered into the intestine was absorbed into the body and transferred and retained mainly in the skin and liver, while dcSTX was hardly retained in the body, although it partly remained in the intestine. In strong contrast, in P. suvattii, little TTX remained in the body, whereas STX was absorbed into the body and was transferred and retained in the ovary and skin. The findings revealed that TTX/PSP selectivity differs between the marine species T. pardalis and the freshwater species P. suvattii. T. pardalis, which naturally harbors TTX, selectively accumulates TTX, and P. suvattii, which naturally harbors PSP, selectively accumulates PSP.

Genome editing of pufferfish saxitoxin- and tetrodotoxin-binding protein type 2 in Takifugu rubripes

The pufferfish saxitoxin- and tetrodotoxin-binding protein 2 (PSTBP2), which is involved in toxin accumulation, was knocked out in Takifugu rubripes embryos by using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 genome-editing technology. Treating the embryos with one of two single-guide RNA (sgRNA) resulted in mutation rates of 57.1% and 62.5%, respectively, as estimated using a heteroduplex mobility assay at 3 days postfertilization. Both sgRNAs might induced frameshift mutations that knocked out the T. rubripes PSTBP2.