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Epigenetic plasticity is a driver of heritable pollution tolerance in Atlantic killifish [ONT Long-read sequencing; DNA]

ABSTRACT: Heritable epigenetic adaptation to environmental stressors is a compelling but highly contested possibility. Previously, we showed evidence of a generationally heritable epigenetic memory at the cytochrome P450 1A (CYP1A) gene in wild Atlantic killifish (Fundulus heteroclitus) with evolved tolerance to PAH. This memory leads to blunted induction of CYP1A by PAH; this blunting that protects against polycyclic aromatic hydrocarbon (PAH)-induced cancer. Here, using Oxford Nanopore long-read sequencing in PAH-tolerant and sensitive wild-type embryos, we show that genome-wide, PAH-tolerant embryos showed reduced plasticity in DNA methylation response to PAH vs. PAH sensitive embryos that was not due to mutational loss of CpG sites. Notably, we observed population differences in gene methylation in pathways linked to the PAH tolerance phenotype, including AHR and voltage-gated potassium channel signaling, as well as developmental processes and energy metabolism. Specifically, we observed PAH-induced loss of CYP1A gene body methylation in PAH-sensitive (86% CpG methylation in control, decreased to 63% in exposed), but not -tolerant (84% control, 86% exposed), embryos. We observed similar patterns at CYP1B, CYP1C, and the aryl hydrocarbon receptor repressor, AHRR, which show similarly blunted expression. This genic methylation loss was correlated with decreased levels of natural anti-sense RNA transcripts in cis (cis-NATs), which may regulate transcription of these genes. Our data support the existence of stable epigenetic responses to chronic environmental stressors in a natural experimental setting, with broad implications for natural or directed adaptation strategies for other populations.

ORGANISM(S): Fundulus heteroclitus

PROVIDER: GSE313974 | GEO | 2026/01/07

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.

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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Epigenetic plasticity is a driver of heritable pollution tolerance in Atlantic killifish [ONT Long-read sequencing; DNA]

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