Project description:The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor well known for mediating the toxicity of environmental chemicals such as polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs). There is extensive knowledge on the range of target genes regulated by AHR ligands. However, there is limited information on the effect of AHR ligands on DNA methylation. The objective of this study is to investigate genome-wide changes in DNA methylation and gene expression patterns in response to PCB126 exposure. Adult zebrafish were exposed to 10 nM PCB126 for 24 hours (waterborne exposure) and were reared in clean water for 7 days before tissue sampling. DNA methylation and transcriptional changes in the liver and brain tissues were quantified by Reduced Representation Bisulfite Sequencing (RRBS) and RNAseq, respectively. RRBS analysis revealed DNA hypomethylation in response to PCB exposure in both liver and brain tissues. We observed 482 and 476 differentially methylated regions (DMRs) in the liver and brain tissues respectively. Most of the DMRs are located more than 20 kilobases upstream of the transcriptional start sites. RNAseq results from the liver revealed differential expression of genes related to xenobiotic metabolism, oxidative stress and carbohydrate metabolism in response to PCB exposure. In the brain, PCB exposure altered the expression of genes involved in myelination and glutamate signaling. Our results suggest that there is very little correlation between DNA methylation and gene expression patterns among the differentially expressed genes (DEGs). We are currently investigating the relationship between DMRs and DEGs.
Project description:Several environmental pollutants, especially organic compounds such as polycyclic aromatic hydrocarbons (PAHs) are potent carcinogenic chemicals. Exposure of different fish species to PAHs causes a high prevalence and variety of tumor lesions. To identify and compare the mode of action (MOA) of different model carcinogenic PAHs, a transcriptomic study was carried out in adult zebrafish (Danio rerio) after exposure to 0.3 mg/l of benzo(a)pyrene (B(a)P) or to 7,12-dimethylbenz(a)anthracene (DMBA), both of them dissolved in dimethyl sulfoxide (DMSO; final concentration of 0.01%). Samples for microarray analysis were taken after 1 and 2 weeks of exposure. The changes in the mRNA transcription levels over the corresponding controls were compared among treatments. Correspondence analysis was able to discriminate among treatments; factor 1 separated both sampling times while factor 2 separated the compounds. A total number of 3043 transcripts was shown to be differentially regulated in at least one of the treatments. B(a)P treatment produced regulation of sequences related to GO categories associated to cell cycle and cell division whereas DMBA regulated GO terms related to oxidation/reduction responses, responses to chemicals and response to bacterium. Both compounds were able to alter many xenobiotic metabolism related genes, especially upregulating the transcription of phase I metabolism-related genes such as cytochrome P450 members (cyp1a or cyp1b), and many cancer-related genes such as the Jun B proto-oncogene (junb). Overall, these results indicated that the exposure to both PAHs was able to differentially alter the transcription levels of genes involved in both the detoxification metabolism and the cell-cycle control, including different tumor-supressor genes and oncogens. These alterations have been often related to the appearance of tumor lesions. Zebrafish were waterborne exposed to 0.3ppm BaP or DMBA for 1 and 2 weeks. After 1 and 2 weeks hepatic samples were collected from each treatment group as well as from the control group. 3 biological replicates have been collected per exposure group and time point. Each biological replicate is a pool of 5 livers. Samples from the different treatments were hybridized in an n+2 (n = 9) A-optimal loop design. Additionally, these two designs were linked by two extra hybridizations to enable comparison between time points
Project description:Zebrafish exposed to 2 waterborne copper concentrations (8 & 15 ug/L) in softwater for 21 days. Fish were terminally sampled and livers extracted for RNA extraction and hybridization to micorarrays
Project description:Waterborne exposure of adult zebrafish to silver nanoparticles and ionic silver results in silver accumulation and effects at cellular and molecular levels
Project description:Polycyclic Aromatic Hydrocarbons (PAHs) are diverse environmental pollutants associated with adverse human health effects. Many studies focus on the carcinogenic effects of a limited number of PAHs and there is an increasing need to understand mechanisms of developmental toxicity of more varied yet environmentally relevant PAHs. A previous study characterized the developmental toxicity of 123 PAHs in zebrafish. Based on phenotypic responses ranging from complete inactivity to acute mortality, we classified these PAHs into eight bins, selected 16 representative PAHs, and exposed developing zebrafish to the concentration of each PAH that induced 80% phenotypic effect. We conducted RNA sequencing at 48 h post fertilization to identify gene expression changes as a result of PAH exposure.
Project description:Development is a complex and well-defined process characterized by rapid cell proliferation and apoptosis. At this stage in life, a developmentally young organism is more sensitive to toxicants and other stressors when compared to an adult. In response to pro-oxidant exposure, members of the Cap’n’Collar (CNC) basic leucine zipper (b-ZIP) transcription factor family (including the Nfe2-related factors, Nrfs) activate the expression of genes that contribute to reduced toxicity. Here, we studied the role of the Nrf protein, Nfe2, in the developmental response to pro-oxidant exposure in the zebrafish. Following acute waterborne exposures to diquat or tert-buytlhydroperoxide (tBOOH) at three developmental stages, wildtype (WT) and nfe2 knockout (KO) embryos and larvae were morphologically scored and their transcriptomes sequenced.
Project description:Effect of 5.4 ppm polycyclic aromatic hydrocarbons (PAHs) and 18.2 ppm alkylphenols (APs) on gene expression in adult Zebrafish (Danio rerio) liver after 1 and 7 weeks of water-borne exposure.
Project description:Pharmaceutical chemicals used in human medicine are released into surface waters via municipal effluents and pose a risk for aquatic organisms. Among these substances are selective serotonin reuptake inhibitors (SSRIs) which can affect aquatic organisms at sub ppb concentrations. To better understand biochemical pathways influenced by SSRIs, evaluate changes in the transcriptome, and identify gene transcripts with potential for biomarkers of exposure to SSRIs; larval zebrafish Danio rerio were exposed (96 h) to two concentrations (25 and 250 µg/L) of the SSRIs, fluoxetine and sertraline, and changes in global gene expression were evaluated (Affymetrix GeneChip® Zebrafish Array). Significant changes in gene expression (>=1.7 fold change, p<0.05) were determined with Partek® Genomics Suite Gene Expression Data Analysis System and ontology analysis was conducted using Molecular Annotation System 3. The number of genes differentially expressed after fluoxetine exposure was 288 at 25 µg/L and 131 at 250 µg/L; and after sertraline exposure was 33 at 25 µg/L and 52 at 250 µg/L. Five genes were differentially regulated in all treatments relative to control, suggesting that both SSRIs share some similar molecular pathways. Among them, expression of the gene coding for FK506 binding protein 5 (FKBP5), which is annotated to stress response regulation, was highly down-regulated in all treatments (results confirmed by qRT-PCR). Gene ontology analysis indicated that regulation of stress response and cholinesterase activity were critical functions influenced by these SSRIs, and suggested that changes in the transcription of FKBP5 or acetylcholinesterase could be useful biomarkers of SSRIs exposure in wild fish. Zebrafish (Danio rerio) were obtained from the Zebrafish Research Facility maintained at the Center for Environmental Biotechnology at the University of Tennessee. Fish husbandry, spawning, and experimental procedures were conducted with approval from the UT Insititutional Animal Care and Use Committee (Protocol #1690-1007). Water for holding fish and conducting experiments (hereafter referred to as fish water) consisted of MilliQ water (Millipore, Bedford, MA) with ions added: 19 mg/L NaHCO3, 1 mg/L sea salt (Instant Ocean Synthetic Sea Salt, Mentor, OH), 10 mg/L CaSO4, 10 mg/L MgSO4, 2 mg/L KCl. Embroyos were obtained by spawning adult fish with no history of contaminant exposure. Fertilization of embryos took place at the same time (<15 minutes), such that larvae used in experiments were of similar age at the time of exposure. All activities (maintenance of adult fish, spawning, and experiments) were conducted in an environmental chamber with a temperature of 27 +/- 1 C and 14:10h light:dark photoperiod. Larval zebrafish (72 hpf) were exposed for 96 h in 200ml fish water containing appropirate amount of SSRI stock (i.e. fluoxetine or sertraline). There were four SSRIs treatments (25 and 250 ug/L fluoxetine and 25 and 250 ug/L sertraline) and one control (no SSRIs) with triplicate beakers and each beaker contained about 100 larval fish. During exposure for 96 hours, beakers were kept covered to prevent water evaporation and fish were not fed (i.e., fish consumed their yolk sac).