Exposure to manganese (II) chloride induces developmental toxicity, oxidative stress and inflammatory response in Marine medaka (Oryzias melastigma) embryos.

Manganese (Mn) is an essential metal for organisms, but high levels can induce serious toxicity. To date, the toxic mechanism of Mn to marine fish is still poorly understood. In the present study, Oryzias melastigma embryos were exposed to different concentrations of MnCl2 (0-152.00 mg/L) to investigate its effect on early development. The results showed that exposure to MnCl2 caused developmental toxicity to embryos, including increased heart rate, delayed hatching time, decreased hatching rate and increased malformation rate. MnCl2 exposure could induce oxidative stress in O. melastigma embryos, as indicated by increased the contents of malondialdehyde (MDA) and the activities of the antioxidant enzymes (superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT)). The heart might be an important target organ for MnCl2 because of cardiac malformations and disruption in the expression of cardiac development-related genes (ATPase, epo, fg8g, cox1, cox2, bmp4 and gata4). In addition, the expression levels of stress- (omTERT and p53) and inflammation-related genes (TNFα and il1ß) were significantly up-regulated, suggesting that MnCl2 can trigger stress and inflammatory response in O. melastigma embryos. In conclusion, this study demonstrated that MnCl2 exposure can induce developmental toxicity, oxidative stress and inflammatory response in O. melastigma embryos, providing insights into the toxic mechanism of Mn to the early development of marine fish.

A new perspective on endocrine disrupting effects of triphenyltin on marine medaka: From brain transcriptome, gut content metabolome and behavior.

Triphenyltin (TPT) is an endocrine contaminant that is often detected in the environment. However, the mechanism of the effects of TPT on biological systems is not fully understood. Here we exposed marine medaka (Oryzias melastigma) to TPT for 21 days. Brain transcriptome, intestinal content metabolism group, and behavior analysis were carried out. Through the comprehensive analysis of multiomics for the in-depth understanding of the ways related to health improvement, we determined that the glycine-serine-threonine metabolic axis was most perturbed by TPT. Through behavioral analysis, it was found that there was behavioral hyperactivity in the exposed group; behavioral hyperactivity may be caused by the interference of TPT with the neuroendocrine system. In order to gain a full understanding of the impacts of TPT on human health, transcriptomic screening of differential genes and an impartial attitude based on bioinformatics were used. Gene-disease interaction analysis using the Comparative Toxicogenomics Database (CTD) revealed the possible effects of TPT on human health. Finally, based on these findings, the relevant adverse outcome pathway (AOP), which is the "epigenetic modification of PPARG leading to adipogenesis," was identified from AOP Wiki. Further research is required to validate the potential AOP of TPT.

Triphenyltin exposure causes changes in health-associated gut microbiome and metabolites in marine medaka.

Triphenyltin (TPT), an organic compound with a wide range of applications, is often detected in water bodies and aquatic animals. However, the mechanism underlying the biological metabolic health problems caused by long-term exposure to environment concentrations of TPT remains unclear. The morphology and gene expression in the gut and liver were investigated; and 16SrRNA gene amplification sequencing and non-targeted LC-MS/MS metabonomics were investigated after marine medaka (Oryzias melastigma) was treated with 1, 10, and 100 ng/L TPT for 21 days. During prolonged exposure to TPT, the adaptation mechanism maximized the energy of absorption, increased the length of intestinal microvilli, reduced the number of rough endoplasmic reticulum in the liver, and caused loss of weight. TPT exposure significantly changed the intestinal microbiome of marine medaka, thereby resulting in a significant decrease in microbial diversity. Following exposure to 100 ng/L TPT, the metabolic profiles were significantly changed and the altered metabolites were mainly concentrated in the lipid metabolic pathway. Finally, based on comprehensive network analysis, the association between the significantly changed bacteria and metabolites contributed further to the prediction of the impact of TPT on the host. This study provides a novel insight into the underlying mechanisms of host metabolic diseases caused by TPT and emphasizes the importance of monitoring pollutants in the environment.

Developmental toxicity in marine medaka (Oryzias melastigma) embryos and larvae exposed to nickel.

As an important trace metal, nickel (Ni) has been reported extensively in the studies on freshwater animals. However, the toxic effects of Ni on marine organisms are not clearly understood. Therefore, in order to investigate the toxic effects of Ni on the early development of marine fish, the marine medaka (Oryzias melastigma) embryos and larvae were immersed in 0.13-65.80 mg/L Ni solution. The results showed that Ni exposure changed the egg size and heart rate of the embryos, lowered the hatchability, increased the deformity rate, and shortened the total body length of newly hatched larvae. Besides, it was found that before organogenesis and post-hatching periods were the sensitive periods of embryos to Ni. The 25 d LC50 value of embryos was 49.28 mg/L, and the 5 d LC50 of larvae was 55.92 mg/L, indicating that the embryos were more sensitive to Ni than the larvae. Furthermore, the expressions of the metallothionein (MT) gene, the skeletal development-related gene (Cyp26b1) and the cardiac development-related genes (ATPase, smyd1, cox2 and bmp4) were determined, and the results showed that the expressions of ATPase and smyd1 were up-regulated, while MT, Cyp26b1 and cox2 were significantly down-regulated at 9 days post-fertilization (dpf). Overall, Ni exposure caused a significant toxic effect on the early development of the O. melastigma embryos and larvae. Our findings could provide an important supplement to the toxicity data of tropical Ni and provide a reference for the exploration of the molecular mechanisms of Ni toxicity.

Both of marine fish species Oryzias melastigma and Pagrus major all failing in early localization at embryo stage by vasa RNA.

Germ cells are essential for gonadal development. As precursors of germ cells, primordial germ cells (PGCs) are particularly important for germline formation. However, the research on distribution patterns of PGCs in marine fish is very limited, especially for economic species. The vasa gene has been widely used as marker to identify PGCs origination and migration because of vasa RNA is a component of germ plasm. In this study, we isolated full-length vasa cDNA (Omvas and Pmvas) from marine medaka (Oryzias melastigma) and red seabream (Pagrus major), detected vasa transcripts in different tissues by RT-PCR and described vasa expression patterns during embryogenesis and gametogenesis by in situ hybridization. At the same time, we also explored the relationship between early distribution of germ plasm components and species evolution. The results demonstrated that deduced amino acid sequence of Omvas and Pmvas shared several conserved motifs of Vasa homologues and high identity with other teleost, and vasa transcripts were exclusively detected in early germ cells of gonad. During embryogenesis, vasa RNA of both fishes, like medaka (Oryzias latipes), failed to localize at cleavage furrows and distributed uniformly throughout each blastomere. This study firstly discovered that the marine economic fish, red seabream, lost vasa RNA early specific localization at cleavage furrows and distinctive distribution in germ cells. In addition, compared with other teleost, we found that early distribution of germ plasm might not relate to species evolution. This will improve our understanding of vasa localization modes in teleost, and facilitate fish germ cell manipulation.

Hemocyte extracellular traps of Manila clam Ruditapes philippinarum: Production characteristics and antibacterial effects.

Extracellular traps (ETs) have been found to be an important strategy of mammals to immobilize and kill invading microorganisms. In the present study, we observed the formation of ETs in the hemocytes of marine mollusks Ruditapes philippinarum in response to challenge from bacteria Vibrio anguillarum, and examined the potential factors and signaling pathways underling this process. We detected an increase of reactive oxygen species (ROS) and myeloperoxidase (MPO) production during ETosis, accompanied by significantly up-regulated expression of ROS-related and MPO genes. The suppression of ETs structures by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor (diphenyleneiodonium chloride, DPI) and MPO inhibitor (aminobenzoic acid hydrazide, ABAH) further confirmed the essential roles ROS and MPO played in ETosis. Furthermore, ET production could be inhibited by phosphotidylinsitol-3-kinase (PI3K) inhibitor (LY294002) and extracellular regulated protein kinase (ERK) inhibitor (U0126), suggesting the idea that both the PI3K and ERK pathways were suggested to function during ETosis. In addition, the ETosis process was accompanied by enhancement of glycolysis-related enzymatic activities, e.g., pyruvate kinase (PK) and hexokinase (HK), and over-expression of the glycolysis-related genes, e.g., PK, HK and glucose transport protein (GLUT), indicating high involvement of glycolysis in the ETosis process. Furthermore, our scanning electron microscopy (SEM) observation and antibacterial activities test successfully showed the patterns how clam ETs entrapped and killed the invading V. anguillarum. Taken together, our results revealed that ETosis with bactericidal effect increased ROS, MPO and glycolysis level and carried out in a ROS-, MPO-, PI3K-ERK-dependent manner.

Molecular characterization, expression and immune functions of two C-type lectin from Venerupis philippinarum.

In the present study, two C-type lectins (designated as VpClec-3 and VpClec-4) were identified and characterized from the manila clam Venerupis philippinarum. Multiple alignment and phylogenetic relationship analysis strongly suggested that VpClec-3 and VpClec-4 belong to the C-type lectin family. In nonstimulated clams, the VpClec-3 transcript was dominantly expressed in the hepatopancreas, while the VpClec-4 transcript was mainly expressed in gill tissues. Both VpClec-3 and VpClec-4 mRNA expression was significantly upregulated following Vibrio anguillarum challenge. Recombinant VpClec-4 (rVpClec-4) was shown to bind lipopolysaccharide (LPS) and glucan in vitro, whereas recombinant VpClec-3 (rVpClec-3) only bound to glucan. In addition, rVpClec-3 and rVpClec-4 displayed broad agglutination activities towards Vibrio harveyi, Vibrio splendidus and V. anguillarum, while no agglutination activities towards Enterobacter cloacae or Aeromonas hydrophila were observed in rVpClec-3. Moreover, hemocyte phagocytosis was significantly enhanced by rVpClec-3 and rVpClec-4. All the results showed that VpClecs function as pattern recognition receptors (PRRs) with distinct recognition spectra and are potentially involved in the innate immune responses of V. philippinarum.