How Genes and DNA Change in Response to Low Oxygen in Pollution-Adapted Fish

Jenn Hoskins
8th January, 2025

How Genes and DNA Change in Response to Low Oxygen in Pollution-Adapted Fish

Mummichog (Fundulus heteroclitus)

Photo adapted from: Zakqary Roy / CC BY (Source)

Key Findings

  • The study examined how Atlantic killifish from New Bedford Harbor (NBH), a polluted site, and Scorton Creek (SC), a cleaner site, respond to low-oxygen conditions (hypoxia)
  • SC killifish adjusted their gene activity based on the severity of hypoxia, while NBH killifish showed a limited gene response to severe hypoxia
  • NBH killifish, which are resistant to industrial pollutants, showed significant changes in DNA methylation under hypoxia, suggesting they rely more on epigenetic mechanisms to cope with low oxygen
Coastal fish populations face significant threats from human activities, including the accumulation of industrial contaminants and the increasing frequency of low-oxygen conditions, known as hypoxia. A recent study conducted by the Woods Hole Oceanographic Institution[1] explored how these combined stressors affect the Atlantic killifish (Fundulus heteroclitus), particularly populations that have developed resistance to industrial pollutants like polychlorinated biphenyls (PCBs). The study focused on killifish from New Bedford Harbor (NBH), a heavily contaminated site, and compared them to a reference population from Scorton Creek (SC), a relatively clean environment. Researchers aimed to understand how PCB resistance might influence the fish's ability to cope with hypoxia, a condition where oxygen levels in the water are significantly reduced. The researchers examined gene expression and DNA methylation patterns in the liver tissues of killifish exposed to mild and severe hypoxia. DNA methylation is a process that can regulate gene expression and is often influenced by environmental factors. The study found notable differences between the two populations. SC fish exhibited dose-dependent changes in gene expression in response to hypoxia, meaning their genes adjusted their activity levels based on the severity of the hypoxic conditions. In contrast, NBH fish showed a muted transcriptional response to severe hypoxia, suggesting that their ability to adjust gene activity in response to low oxygen was compromised. Interestingly, NBH fish displayed significant changes in DNA methylation in response to hypoxia, while SC fish did not show notable epigenetic alterations. This indicates that the NBH population, which has adapted to high levels of PCBs, may rely more on epigenetic mechanisms to cope with environmental stressors like hypoxia. These findings suggest that the evolutionary trade-offs associated with PCB resistance might impact the fish's ability to survive in hypoxic conditions. This study builds on previous research that has shown the complex relationship between environmental toxicants, gene expression, and DNA methylation. For example, earlier research demonstrated that exposure to PCB126 in zebrafish led to genome-wide changes in DNA methylation and gene expression, with little correlation between the two[2]. This highlights the dynamic and complex nature of the relationship between methylation and gene expression. Additionally, the current findings align with studies on other fish species exposed to hypoxia. Research on hybrid striped bass revealed that chronic hypoxia affects lipid metabolism, cell death, and mitochondrial function, demonstrating the broad impact of low oxygen on fish physiology[3]. Furthermore, studies on killifish from polluted environments have shown that these fish develop resistance to toxicants like PCBs, which can alter their physiological responses to other stressors[4]. The new study suggests that while PCB-resistant killifish have adapted to survive in contaminated environments, this adaptation may come at a cost. The muted gene expression response to hypoxia in NBH fish could compromise their ability to survive in coastal habitats where hypoxic events are becoming more frequent. The significant DNA methylation changes observed in NBH fish indicate that epigenetic regulation plays a crucial role in their stress response, but the long-term implications of these changes are not yet fully understood. Further research is needed to explore the functional consequences of these epigenetic modifications and their role in adaptive stress responses. Understanding how toxicant resistance influences the ability of coastal fish populations to cope with multiple environmental stressors is essential for developing effective conservation strategies in the face of ongoing environmental change.

GeneticsBiochemMarine Biology

References

Main Study

1) Gene expression and DNA methylation changes in response to hypoxia in toxicant-adapted Atlantic killifish (Fundulus heteroclitus).

Published 15th January, 2025 (future Journal edition)

https://doi.org/10.1242/bio.061801

Related Studies

2) Role of DNA methylation in altered gene expression patterns in adult zebrafish (Danio rerio) exposed to 3, 3', 4, 4', 5-pentachlorobiphenyl (PCB 126).

https://doi.org/10.1093/eep/dvy005

3) Hepatic transcriptomic and metabolic responses of hybrid striped bass (Morone saxatilis×Morone chrysops) to acute and chronic hypoxic insult.

https://doi.org/10.1016/j.cbd.2016.01.005

4) Acquired resistance to Ah receptor agonists in a population of Atlantic killifish (Fundulus heteroclitus) inhabiting a marine superfund site: in vivo and in vitro studies on the inducibility of xenobiotic metabolizing enzymes.

Journal: Toxicological sciences : an official journal of the Society of Toxicology, Issue: Vol 60, Issue 1, Mar 2001


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