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Aryl hydrocarbon receptor mediates larval zebrafish fin duplication following exposure to benzofluoranthenes.

ABSTRACT: Polycyclic aromatic hydrocarbons (PAHs) can alter gene expression by acting through the aryl hydrocarbon receptor (AHR). In a previous phenotypic screen of over 120 PAHs, we identified four PAHs that induce an ectopic caudal fin (called X-fin) in larval zebrafish: benzo[k]fluoranthene (BkF), dibenzo[b,k]fluoranthene, dibenzo[a,h]anthracene, and benzo[j]fluoranthene. We investigated several plausible mechanisms of X-fin formation using the most potent X-fin inducer, BkF. The X-fin phenotype was dependent on the AHR paralog Ahr2, and we performed RNA sequencing to identify altered gene expression patterns. Transcriptional profiles of distal trunk tissue, where the phenotype was manifest, were generated for animals exposed to 1% DMSO (control) or 12 μM BkF. Four time points of X-fin development were considered for transcriptomics: prior to visual emergence of X-fin (48 hpf), during manifestation of disrupted caudal fin fold development (60 and 72 hpf), and after emergence of X-fin (96 hpf).

ORGANISM(S): Danio rerio

PROVIDER: GSE143945 | GEO | 2020/01/21

REPOSITORIES: GEO

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Project description:Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment as components of fossil fuels and by-products of combustion. These multi-ring chemicals differentially activate the Aryl Hydrocarbon Receptor (AHR) in a structurally-dependent manner, and induce toxicity via both AHR-dependent and -independent mechanisms. PAH exposure is known to induce developmental malformations in zebrafish embryos, and recent studies have shown cardiac toxicity induced by compounds with low AHR affinity. Unraveling the potentially diverse molecular mechanisms of PAH toxicity is essential for understanding the hazard posed by complex PAH mixtures present in the environment. We analyzed transcriptional responses to PAH exposure in zebrafish embryos exposed to benz(a)anthracene (BAA), dibenzothiophene (DBT) and pyrene (PYR) at a concentration that induces developmental malformations by 120 hours post-fertilization (hpf). Whole genome microarray analysis of mRNA expression at 24 and 48 hpf identified genes that were differentially regulated over time and in response to the three PAH structures. PAH body burden was analyzed at these time points using GC-MS, and demonstrated differences in PAH uptake into the embryos. This was important for discerning dose-related differences from those that represented unique molecular mechanisms. While BAA misregulated the smallest number of transcripts, it caused strong induction of cyp1a and other genes known to be downstream of the AHR, which were not induced by the other two PAHs. Analysis of functional roles of misregulated genes and their predicted regulatory transcription factors also distinguished the BAA response from regulatory networks disrupted by DBT and PYR exposure. These results indicate that systems approaches can be used to classify the toxicity of PAHs based on the networks perturbed following exposure and may provide a path for unraveling the toxicity of complex PAH mixtures. Gene expression was measured in zebrafish embryos after exposure to PAHs. Embryos were batch-exposed in groups of 40 to 25 μM BAA, 25 μM DBT, 25 μM PYR or 1% DMSO vehicle control starting at 6 hpf and collected at 24 or 48 hpf. Four independent biological replicates were prepared for each treatment. The reference was a pool of zebrafish embryos exposed to DMSO control until 24 and 48 hpf.

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Aryl hydrocarbon receptor mediates larval zebrafish fin duplication following exposure to benzofluoranthenes.

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