Project description:Domoic acid (DA) is a naturally produced neurotoxin synthesized by the marine diatom genus Pseudo-nitzschia. DA accumulates in filter-feeders such as shellfish, and can produce severe neurotoxicity when contaminated seafood is ingested. DA poisoning is a significant public health concern, and though seafood regulations have effectively minimized the human risk of severe acute poisoning, the effects of exposure at asymptomatic levels are poorly understood. The objective of this study was to determine the effects of exposure to symptomatic and asymptomatic doses of DA on gene expression patterns in the zebrafish brain. We exposed adult zebrafish to either a symptomatic (1.1 ± 0.2 μg /g) or an asymptomatic (0.31 ± 0.03 µg DA/g fish) dose of DA by intracelomic injection and sampled at 24, 48 and 168 h post-injection. Transcriptional profiling was done using Agilent and Affymetrix microarrays. Our analysis revealed distinct, non-overlapping changes in gene expression between the two doses. We found that the majority of transcriptional changes were observed at 24 hours post-injection with both doses. In response to symptomatic dose exposure, we observed 328, 5, and 1 genes were differentially expressed at 24, 48 and 168 hours post-injection, respectively. In contrast, 136, 12, and 28 genes were differentially expressed in the asymptomatic dose at the same time points. Pathway analysis revealed symptomatic DA exposure affected genes associated with pathways including cell adhesion, inflammation, and amyloid proteins. Among the pathways enriched among genes differentially expressed with asymptomatic exposure were circadian rhythms and endocrine signaling. Overall, these results suggest that transcriptional responses are specific to the DA dose and that asymptomatic exposure can cause long-term changes. Many of the differentially expressed genes are important players in neuronal, neuroimmune and neuroendocrine function. Further studies are needed to characterize the potential downstream neurobehavioral impacts of DA exposure.

Project description:Domoic acid (DA) is a neuroexcitatory amino acid that is naturally produced by some marine diatom species of the genus Pseudo-nitzschia. Ingestion of DA-contaminated seafood by humans results in a severe neurotoxic disease known as amnesic shellfish poisoning (ASP). Clinical signs of ASP include seizures and neuronal damage from activation of AMPA and kainate receptors. However, the impacts of DA exposure at levels below those known to induce outward signs of neurobehavioral exicitotoxicity have not been well characterized. To further understand the mechanisms of neurotoxic injury associated with DA exposure, we examined the transcriptome of whole brains from zebrafish (Danio rerio) receiving intracoelomic (IC) DA at both symptomatic and asymptomatic doses. A majority of zebrafish exposed to high-dose DA (1.2 µg DA/g) exhibited clinical signs of neuroexcitotoxicity (EC50 of 0.86 µg DA/g) within 5 to 20 minutes of IC injection. All zebrafish receiving low-dose DA (0.47 µg DA/g) or vehicle only maintained normal behavior. Microarray analysis of symptomatic and asymptomatic exposures collectively yielded 306 differentially expressed genes (1.5-fold, p = 0.05) predominately represented by signal transduction, ion transport, and transcription factor functional categories. Transcriptional profiles were suggestive of neuronal apoptosis following an overwhelming of protective adaptive pathways. Further, potential molecular biomarkers of neuropathic injury, including Nrdg4, were identified and may be relevant to DA exposure levels below that causing neurobehavioral injury. Our results validate zebrafish as a vertebrate model to study mechanisms of DA neurotoxicity and provide a basis for identifying pathways of DA-induced injury as well as biomarkers of asymptomatic and symptomatic DA exposure levels. Keywords: neurotoxic disease To further understand the mechanisms of neurotoxic injury associated with DA exposure, we examined the transcriptome of whole brains from zebrafish (Danio rerio) receiving intracoelomic (IC) DA at both symptomatic and asymptomatic doses. A majority of zebrafish exposed to high-dose DA (1.2 µg DA/g) exhibited clinical signs of neuroexcitotoxicity (EC50 of 0.86 µg DA/g) within 5 to 20 minutes of IC injection. All zebrafish receiving low-dose DA (0.47 µg DA/g) or vehicle only maintained normal behavior. Microarray analysis of symptomatic and asymptomatic exposures collectively yielded 306 differentially expressed genes (1.5-fold, p = 0.05) predominately represented by signal transduction, ion transport, and transcription factor functional categories. All animal studies were carried out under approved IACUC protocols at the University of Washington.

Project description:Congenital malformations are a prevalent cause of infant mortality in the United States and their induction has been linked to a variety of factors, including exposure to teratogens. However, the molecular mechanisms of teratogenicity are not fully understood. MicroRNAs are an important group of small, non-coding RNAs that regulate mRNA expression. MicroRNA roles in early embryonic development are well established, and their disruption during development can cause abnormalities. We hypothesized that developmental exposure to teratogens such as valproic acid alters microRNA expression profiles in developing embryos. Valproic acid is an anticonvulsant and mood-stabilizing drug used to treat epilepsy, bipolar disorder and migraines. To examine the effects of valproic acid on microRNA expression during development, we used zebrafish embryos as a model vertebrate developmental system. Zebrafish embryos were continuously exposed to valproic acid (1 mM) or vehicle control (ethanol) starting from 4 hours post-fertilization (hpf) and sampled at 48 and 96 hpf to determine the miRNA expression profiles prior to and after the onset of developmental defects. At 96 hpf, 95% of the larvae showed skeletal deformities, abnormal swimming behavior, and pericardial effusion. Microarray expression profiling was done using Agilent zebrafish miRNA microarrays. Microarray results revealed changes in miRNA expression at both the time points. Thirteen miRNAs were differentially expressed at 48 hpf and 22 miRNAs were altered at 96 hpf. Among them, six miRNAs (miR-16a, 18c, 122, 132, 457b, and 724) were common to both time points. Bioinformatic target prediction and examination of published literature revealed that these miRNAs target several genes involved in the normal functioning of the central nervous system. These results suggest that the teratogenic effects of valproic acid could involve altered miRNA expression. Small RNA profiles were deteremined in valproic acid exposed zebrafish embryos using Agilent miRNA microarrays

Project description:Perfluorooctanoic acid (PFOA) is one of the most used perfluorinated compounds in numerous applications and can be detected in environmental samples from around the globe. The aquatic environment is an important site for PFOA deposit. Nevertheless, the exact mode of action and its resulting toxicological effects on aquatic organisms remain largely unknown. To gain a more extensive understanding of the mode of action of teleost PFOA toxicity, transcriptomics, proteomics, biochemical parameters and reproduction were integrated in the present study. Male and female zebrafish were exposed to nominal concentrations of 0.1; 0.5 and 1 mg/l PFOA for 4 and 28 days resulting in an accumulation which was higher in males compared to females. These gender-related differences were likely caused by different elimination rates due to distinct hormone levels and differences in transport activity by solute carriers. The general mode of action of PFOA was believed to be an increase of the mitochondrial membrane permeability which caused effects on the electron transport system at the biochemical level and resulted in alterations of the oxidative phosphorylation, oxidative stress and apoptosis at the gene transcript and protein level. As a consequence, evidence for the replacement of the affected cells and organelles to sustain tissue homeostasis was found at the molecular level. The higher energy demand, due to these adverse effects, was provided by lowering the glycogen stores. Despite this increase in metabolic expenditure, no effects on reproduction were found indicating that the fish seemed to cope with exposure to the tested concentrations of PFOA. Adult zebrafish (Danio rerio) were exposed to nominal concentrations of 0mg/l; 0.1mg/l; 1mg/l PFOA (perfluorooctanoic acid) for 28 days. Three different 25 litre aquaria per exposure concentration were used resulting in 3 biological replicates with each aquarium containing 8 male and 8 female zebrafish. The livers of 6 male fish and 6 female fish were pooled separately and snap frozen in liquid nitrogen. A reference sample was made by pooling equal amounts of RNA from all samples. A carriage wheel design was used in which all samples were connected to the reference sample and the main contrasts of interest were made directly on the same microarrays as frequently as possible. This design resulted in technical triplicates of each sample.

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Symptomatic Domoic Acid exposure in zebrafish

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