Expression of the genes siamois, engrailed-2, bmp4 and myf5 during Xenopus development in presence of the marine toxins okadaic acid and palytoxin

A study on the mechanism of the impact of phenthoate exposure on Prorocentrum lima

Extensive application of organophosphorus pesticides such as phenthoate results in its abundance in ecosystems, particularly in waterbodies, thereby providing the impetus to assess its role in aquatic organisms. However, the impact of phenthoate on marine algal physiological and proteomic response is yet to be explored despite its biological significance. In this study, we thus ought to investigate the impact of phenthoate in the marine dinoflagellate Prorocentrum lima, which is known for synthesizing okadaic acid (OA), the toxin responsible for diarrhetic shellfish poisoning (DSP). Our results showed that P. lima effectively absorbed phenthoate in seawater, with a reduction efficiency of 90.31% after 48 h. Surprisingly, the provision of phenthoate (100 and 1000 µg/L) substantially reduced the OA content of P. lima by 35.08% and 60.28% after 48 h, respectively. Meanwhile, phenthoate treatment significantly reduced the oxidative stress in P. lima. Proteomic analysis revealed that the expression level of seven crucial proteins involved in endocytosis was upregulated, suggesting that P. lima could absorb phenthoate via the endocytic signaling pathway. Importantly, phenthoate treatment resulted in the downregulation of proteins such as polyketide synthase (PKS)- 2, Cytochrome P450 (CYP450)- 1, and CYP450-2, involved in OA synthesis, thereby decreasing the OA biosynthesis by P. lima. Our results demonstrated the potential role of P. lima in the removal of phenthoate in water and exemplified the crucial proteins and their possible molecular mechanisms underpinning the phenthoate remediation by P. lima and also the regulatory role of phenthoate in restricting the OA metabolism. Collectively, these findings uncovered the synergistic mechanisms of phenthoate and P. lima in remediating phenthoate and reducing the toxic impact of P. lima.

Molecular mechanisms of zooplanktonic toxicity in the okadaic acid-producing dinoflagellate Prorocentrum lima

Prorocentrum lima is a dinoflagellate that forms hazardous blooms and produces okadaic acid (OA), leading to adverse environmental consequences associated with the declines of zooplankton populations. However, little is known about the toxic effects and molecular mechanisms of P. lima or OA on zooplankton. Here, their toxic effects were investigated using the brine shrimp Artemia salina. Acute exposure of A. salina to P. lima resulted in lethality at concentrations 100-fold lower than densities observed during blooms. The first comprehensive results from global transcriptomic and metabolomic analyses in A. salina showed up-regulated mRNA expression of antioxidant enzymes and reduced non-enzyme antioxidants, indicating general detoxification responses to oxidative stress after exposure to P. lima. The significantly up-regulated mRNA expression of proteasome, spliceosome, and ribosome, as well as the increased fatty acid oxidation and oxidative phosphorylation suggested the proteolysis of damaged proteins and induction of energy expenditure. Exposure to OA increased catabolism of chitin, which may further disrupt the molting and reproduction activities of A. salina. Our data shed new insights on the molecular responses and toxicity mechanisms of A. salina to P. lima or OA. The simple zooplankton model integrated with omic methods provides a sensitive assessment approach for studying hazardous algae.

Embryotoxic effects of dissolved okadaic acid on the development of Longfin yellowtail Seriola rivoliana

In the context of global climate change where harmful algal blooms (HABs) might become more frequent and more severe, several studies have been conducted on the perturbation of embryonic development of marine animals by microalgal toxins. Okadaic acid (OA) and analogs (DSP toxins) produced by dinoflagellates of the genera Dynophysis and Prorocentrum are known to disturb embryogenesis. This study investigated the impact of dissolved DSP toxin (OA and Dinophysistoxin 1, DTX-1) exposure on embryo development of Longfin yellowtail Seriola rivoliana. Eggs were exposed to different concentrations of dissolved DSP toxins (low treatment: at 120μgl^-1 OA eq; high treatment 175μgl^-1 OA eq.). The first objective was to study the global toxic effect of DSP toxins with hatching percentages. Secondly, the effect of these toxins was investigated at molecular and functional level by measuring expression of responsible genes for bone morphogenetic protein (BMP) and proliferating cell nuclear antigen (PCNA) measuring phosphatase enzyme (serine/threonine and alkaline phosphatases) activities. Our results showed drastic mortalities induced by DSP toxins in both low and high concentration treatments. Activities of both protein and alkaline phosphatases were significantly inhibited by DSP toxin treatments, whose effects on gene expression were less evident, but levels of BMP expression in eggs treated with the lowest toxin concentration were significantly different from that in the control treatment. This work revealed an embryotoxic effect of DSP toxins resulting in high mortality of eggs. Phosphatase inhibition could have participated in part in these global effects by perturbing the regulation of pathways related to embryogenesis and resulting in a perturbation of gene expression.

Exposure of okadaic acid alters the angiogenesis in developing chick embryos

Okadaic acid (OA) is a common phycotoxin, which concerns diarrheic shellfish poisoning (DSP) in human being. It has been known that OA can induce disorganization in cytoskeletal architecture and cell-cell contact, cause chromosome loss, apoptosis, DNA damage and inhibit phosphatases, suggesting its potential embryotoxicity. In this paper, we found that low concentration of OA (50 nM, 100 nM and 200 nM) significantly reduced the density of vascular plexus in yolk-sac membrane (YSM) of chick embryo, while high concentration of OA (500 nM) distinctly depressed the blood vessel density in chorioallantoic membrane (CAM). After exposed to OA, MDA level and SOD activity increased significantly in CAM tissues. However, addition of vitamin C could rescue OA-suppressed angiogenesis in CAM of chick embryo. After exposure of OA, Ang-2 expression was down-regulated in CAM tissues. Taking together, we proposed that OA interfered with angiogenesis in developing chick embryo, through, at least partly, the induction of excessive ROS generation.

Chlorpyrifos exposure affects fgf8, sox9, and bmp4 expression required for cranial neural crest morphogenesis and chondrogenesis in Xenopus laevis embryos

Chlorpyrifos (CPF) is an organophosphate insecticide used primarily to control foliage and soil-borne insect pests on a variety of food and feed crops. In mammals, maternal exposure to CPF has been reported to induce dose-related abnormalities such as slower brain growth and cerebral cortex thinning. In lower vertebrates, for example, fish and amphibians, teratogenic activity of this compound is correlated with several anatomical alterations. Little is known about the effects of CPF on mRNA expression of genes involved in early development of the anatomical structures appearing abnormal in embryos. This study investigated the effects of exposure to different CPF concentrations (10, 15 and 20 mg/L) on Xenopus laevis embryos from stage 4/8 to stage 46. Some of the morphological changes we detected in CPF-exposed embryos included cranial neural crest cell (NCC)-derived structures. For this reason, we analyzed the expression of select genes involved in hindbrain patterning (egr2), cranial neural crest chondrogenesis, and craniofacial development (fgf8, bmp4, sox9, hoxa2 and hoxb2). We found that CPF exposure induced a reduction in transcription of all the genes involved in NCC-dependent chondrogenesis, with largest reductions in fgf8 and sox9; whereas, in hindbrain, we did not find any alterations in egr2 expression. Changes in the expression of fgf8, bmp4, and sox9, which are master regulators of several developmental pathways, have important implications. If these changes are confirmed to belong to a general pattern of alterations in vertebrates prenatally exposed to OP, they might be useful to assess damage during vertebrate embryo development. Environ. Mol. Mutagen. 57:589-604, 2016. © 2016 Wiley Periodicals, Inc.

Detection, occurrence and monthly variations of typical lipophilic marine toxins associated with diarrhetic shellfish poisoning in the coastal seawater of Qingdao City, China

In recent years, related research has mainly examined lipophilic marine toxins (LMTs) in contaminated bivalves or toxic algae, whereas the levels of LMTs in seawater remain largely unexplored. Okadaic acid (OA), yessotoxin (YTX), and pectenotoxin-2 (PTX2) are three typical LMTs produced by certain marine algae that are closely linked to diarrhetic shellfish poisoning. In this study, a new method of solid phase extraction combined with liquid chromatography - electrospray ionization ion trap tandem mass spectrometry was developed to determine the presence of OA, YTX, and PTX2 in seawater simultaneously. Satisfactory sensitivity, repeatability (RSD<25.00%) and recovery (56.25-70.18%) of the method were achieved. Then, the method was applied to determine the amounts of the three toxins in the coastal seawater. OA and PTX2 were detected in all the seawater samples collected from eight locations along the coastline of Qingdao City, China on October 23, 2012, with concentration ranges of OA 4.24-9.64ngL(-1) and PTX2 0.42-0.74ngL(-1). Monthly concentrations of OA and PTX2 in the seawater of four locations were determined over the course of a year, with concentration ranges of OA 1.41-89.52ngL(-1) and PTX2 below detectable limit to 1.70ngL(-1). The peak values of OA and PTX2 in coastal seawater were observed in August and July, respectively. Our results suggest that follow-up research on the fate modeling and risk assessment of LMTs in coastal seawater should be implemented.

Gene expression profiles in zebrafish (Danio rerio) liver after acute exposure to okadaic acid

Okadaic acid (OA), a main component of diarrheic shellfish poisoning (DSP) toxins, is a strong and specific inhibitor of the serine/threonine protein phosphatases PP1 and PP2A. However, not all of the OA-induced effects can be explained by this phosphatase inhibition, and controversial results on OA are increasing. To provide clues on potential mechanisms of OA other than phosphatase inhibition, here, acute toxicity of OA was evaluated in zebrafish, and changes in gene expression in zebrafish liver tissues upon exposure to OA were observed by microarray. The i.p. ED50 (6 h) of OA on zebrafish was 1.54 μg OA/g body weight (bw). Among the genes analyzed on the zebrafish array, 55 genes were significantly up-regulated and 36 down-regulated in the fish liver tissue upon exposure to 0.176 μg OA/g bw (low-dose group, LD) compared with the low ethanol control (LE). However, there were no obvious functional clusters for them. On the contrary, fish exposure to 1.760 μg OA/g bw (high-dose group, HD) yielded a great number of differential expressed genes (700 up and 285 down) compared with high ethanol control (HE), which clustered in several functional terms such as p53 signaling pathway, Wnt signaling pathway, glutathione metabolism and protein processing in endoplasmic reticulum, etc. These genes were involved in protein phosphatase activity, translation factor activity, heat shock protein binding, as well as transmembrane transporter activity. Our findings may give some useful information on the pathways of OA-induced injury in fish.

Gene expression responses for detecting sublethal effects of xenobiotics and whole effluents on a Xenopus laevis embryo assay

In the present study, the authors investigated the effects of bisphenol A, chlorpyrifos, methylparaben, and 2 effluent samples from wastewater treatment plants located in the province of Madrid, Spain, on the messenger RNA expression of specific genes involved in early development (ESR1, pax6, bmp4, and myf5) and a gene involved in the general stress response (hsp70) during Xenopus laevis embryo development. Gene expression was analyzed after 4 h, 24 h, and 96 h of exposure by semiquantitative reverse-transcriptase-polymerase chain reaction. Concentration ranges of the compounds and dilutions for the samples were selected to cause morphological alterations in embryos after 96 h of exposure. Transcript levels of ESR1, pax6, and hsp70 were differentially altered at early developmental stages with patterns specific to the contaminant and the exposure time. However, further studies are needed to establish transcript levels of specific genes as biomarkers of sublethal effects in an environmental risk-assessment framework. Besides, studies including more generic responses, such as genes encoding antioxidant enzymes, together with genes related to embryonic development have to be developed to look for a battery of mechanistic endpoints for the evaluation of chemical exposure at the molecular level in a first-tier assessment.

Tail regenerative capacity and iNOS immunolocalization in Xenopus laevis tadpoles

The morphology and the immuno-distribution of the inducible isoform of nitric oxide synthase (iNOS) have been examined in regenerating tails from differently aged Xenopus laevis larvae. By comparing stage-50 and stage-55/56 tadpoles, various morphological aspects and immunoreactivity to anti-iNOS antibody in terms of the number and duration of positive cells have been demonstrated in the regenerating buds. Unlike in stage-50 larvae, the extent of responses to tail amputation in older larvae is more dependent on the individual tadpole and a high percentage (70%-80%) of malformed tails has been seen. The findings indicate that the decline in the efficiency of Xenopus tail regeneration is driven by differences in the inflammatory responses and in the involvement of nitric oxide. This molecule is induced and required for normal tail regeneration, whereas in excess, it is probably associated with progressive loss in the regeneration capability.

Targets and effects of yessotoxin, okadaic acid and palytoxin: a differential review

In this review, we focus on processes, organs and systems targeted by the marine toxins yessotoxin (YTX), okadaic acid (OA) and palytoxin (PTX). The effects of YTX and their basis are analyzed from data collected in the mollusc Mytilus galloprovincialis, the annelid Enchytraeus crypticus, Swiss CD1 mice and invertebrate and vertebrate cell cultures. OA and PTX, two toxins with a better established mode of action, are analyzed with regard to their effects on development. The amphibian Xenopus laevis is used as a model, and the Frog Embryo Teratogenesis Assay-Xenopus (FETAX) as the experimental protocol.

Effects of marine toxins on the reproduction and early stages development of aquatic organisms

Marine organisms, and specially phytoplankton species, are able to produce a diverse array of toxic compounds that are not yet fully understood in terms of their main targets and biological function. Toxins such as saxitoxins, tetrodotoxin, palytoxin, nodularin, okadaic acid, domoic acid, may be produced in large amounts by dinoflagellates, cyanobacteria, bacteria and diatoms and accumulate in vectors that transfer the toxin along food chains. These may affect top predator organisms, including human populations, leading in some cases to death. Nevertheless, these toxins may also affect the reproduction of aquatic organisms that may be in contact with the toxins, either by decreasing the amount or quality of gametes or by affecting embryonic development. Adults of some species may be insensitive to toxins but early stages are more prone to intoxication because they lack effective enzymatic systems to detoxify the toxins and are more exposed to the toxins due to a higher metabolic growth rate. In this paper we review the current knowledge on the effects of some of the most common marine toxins on the reproduction and development of early stages of some organisms.