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Developmental Exposure To PCB153 Alters Genes Related To Circadian Rhythm And Metabolism In Zebrafish (Danio rerio)

ABSTRACT: Polychlorinated biphenyls (PCBs) are persistent and ubiquitously distributed environmental pollutants. Based on their chemical structure, PCBs are classified into non-ortho substituted and ortho-substituted congeners. Non-ortho-substituted PCBs are structurally similar to dioxin or TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) and their mode of action and toxic effects are well established. In contrast, much less is known about the effects of ortho-substituted PCBs. Studies conducted so far have focused on tissue-specific effects but there is limited knowledge about the effects on the whole organism, particularly the sensitive developmental stages in vertebrates. Hence, in this study we investigated the effects of exposure to an environmentally relevant ortho-substituted PCB (2,2’,4,4’,5,5’-hexachlorobiphenyl; PCB153) on zebrafish embryos. We exposed zebrafish embryos to either DMSO (0.1%; solvent control) or three different concentrations of PCB153 (0.1, 1 and 10 μM) from 4 hours post-fertilization (hpf) to 120 hpf. At the end of the exposure, larvae were sampled for determining transcriptional changes (RNA sequencing) and the remaining embryos were maintained in contaminant-free environment. At 7 and 14 days post-fertilization (dpf), zebrafish larvae were assessed for locomotory behavior. We did not observe any overt phenotypes during the exposure period, but observed a spinal phenotype in the 10μM PCB153 treated group starting at 7 dpf. This phenotype was observed in a dose-dependent manner and majority of the embryos with this phenotype died by 14 dpf. RNA sequencing of 5 dpf larvae exposed to PCB153 also revealed dose-dependent changes in gene expression patterns. A total of 633, 2227, and 3378 differentially expressed genes were observed in 0.1, 1 and 10 μM PCB153 treated embryos, respectively. Among these, 301 genes were common to all treatment groups, and KEGG pathway analysis revealed enrichment of genes related to circadian rhythm, FOXO signaling and insulin resistance pathways. We are currently investigating the functions of genes that are uniquely altered by different PCB153 concentrations. Overall, these results suggest that developmental exposure to PCB153, a PCB congener highly prevalent in the environment, targets multiple physiological processes including photoperiod regulation and metabolism. [Funded by NIH P01ES021923 and NSF OCE-1314642].

ORGANISM(S): Danio rerio

PROVIDER: GSE93310 | GEO | 2017/12/31

SECONDARY ACCESSION(S): PRJNA360585

REPOSITORIES: GEO

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Project description:This study presents statistical analyses of gene expression in 5, 10 and 15 day post-fertilization (dpf) embryos of the teleost Fundulus heteroclitus treated with control vehicle (DMSO) or a potent non-ortho-PCB (PCB-126; 3,3’,4,4’,5-pentachlorobiphenyl). The embryos were from two populations: a clean, reference population (SC, Scorton Creek, MA USA) and a polluted Superfund population (N, New Bedford Harbor, MA USA). For each site, eggs from 8 females (~1100 total) were fertilized using minced testes from 5 males. After non-fertile eggs were culled, embryos were exposed to vehicle (DMSO; 0.1%) or PCB-126 (50 nM) in filtered seawater (salinity 25 part per thousand, 65 embros per 20 ml in glass petri dish) for 4 hr at 20º C. After exposure, the embryos were washed in filtered seawater and incubated at 20º C under a 14-h light, 10-h dark cycle. At 5-, 10-, and 15-dpf, embryos were collected as three pools of 20 embryos from each treatment group and flash frozen in liquid nitrogen and stored at -80º C until used for RNA isolation. A loop design was used for the microarray hybridizations where each sample is hybridized to 2 arrays using both Cy3 and Cy5 labeled fluorophores. We used three loops in which each loop consisted of Cy3- and Cy5-labeled embryo aRNAs from 12 samples: one sample from each population-treatment-time combination. Within a population-treatment-time, embryos were randomly assigned to one of the three loops. In total, 36 embryos were hybridized to 36 microarrays. The loops formed were SC5C→ SC5P → NBH5C→ NBH5P →SC10C→ SC10P→ NBH10C→ NBH10P → SC15C→ SC15P → NBH15C → NBH15P → SC5C, where each arrow represents a separate hybridization (array) with the biological sample at the base of the arrow labeled with Cy3 and the biological sample at the head of the arrow labeled with Cy5. SC represents the Scorton Creek, Sandwich, MA population (reference), NBH represents the New Bedford Harbor, MA population, C represents control dose (DMSO), P represents the PCB-126 dose, 5 represents 5 dpf, 10 represents 10 dpf and 15 represents 15 dpf.

Project description:There is growing evidence from epidemiological and experimental studies suggesting that early life exposure to environmental chemicals can have long-term consequences that are seen in adults and not apparent early in life. We recently demonstrated that developmental exposure of zebrafish embryos to low, non-embryotoxic levels of PCB126 did not affect larval behavior but caused changes in adult behavior (Glazer et al., 2016, NeuroToxicology 52:134-143). Zebrafish embryos were exposed to either vehicle (DMSO) or low concentrations of PCB126 (0.3, 0.6, 1.2 nM) for 20 h (4–24 h post fertilization), and then reared to adulthood in clean water. Locomotor activity of the larvae at 7 and 14 days post fertilization (dpf) was not affected by PCB126. In contrast, adult fish (4 months old) tested in novel tank and shoaling assays showed impaired habituation to a novel environment. In order to investigate the underlying molecular basis of these phenotypes, we determined the transcriptional profiles in whole embryos (48 hpf), larvae (5 dpf) and adult brain (4 mo) using strand-specific RNA-sequencing. Our results show that 0.3 nM PCB126 exposure induced cyp1a transcript levels 12.5-fold in 48-hpf embryos but there was no induction in 5-dpf larvae, suggesting transient activation of aryl hydrocarbon receptor during early development. No significant induction of cyp1a was observed in the brains of adults exposed as embryos to PCB126. However, we observed significant changes in gene expression profiles in the adult brain samples. A total of 2209 and 1628 genes were differentially expressed in 0.3 nM and 1.2 nM PCB126-exposed groups, respectively. KEGG pathway analysis of differentially expressed genes in the brain suggest enrichment of genes involved in oxidative phosphorylation, neurodegenerative diseases, circadian rhythm and calcium signaling pathways. We are currently investigating the role of these genes in altered behavior observed in the adults. Overall, our results suggest that PCB exposure during sensitive periods of early development alters normal development of the brain by reprogramming gene expression patterns. [Funded by NIH P01ES021923 and NSF OCE-1314642].

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Developmental Exposure To PCB153 Alters Genes Related To Circadian Rhythm And Metabolism In Zebrafish (Danio rerio)

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