ET&C Focus on Epigenetics for Ecotoxicologists
Jane A. Parkin Kullmann, Haley & Aldrich, Inc.
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The February 2012 ET&C features a Focus article by Jessica Head, Dana Dolinoy and Niladri Basu on epigenetics, the science of how genes and the environment interact. Recently, epigenetics has been featured as a way to assess latent and intergenerational health effects from chemical exposures. The February ET&C Focus talks about the links between epigenetics and ecotoxicology and suggests exciting avenues for future research, making it particularly interesting reading for SETAC student members!
The authors describe epigenetics as the study of gene expression created from "chemical marks" on DNA code. They talk about the discovery that these epigenetic marks have been found to influence the expression of the underlying genes, both in nature and degree. They talk about two particular types of epigenetic marks: DNA methylation and histone modification. With these marks, the genes are changed either with respect to their degree of methylation (with highly methylated genes being less likely to be expressed) or via modifications to their histone tails.
One implication of epigenetics is that past experiences can shape future gene expression, resulting in latent effects from exposures that occur earlier in life. The authors talk about epigenetic modifications that might be responsible for negative health outcomes. One interesting aspect of epigenetics noted by the authors is that its mechanisms provide support for the "Barker hypothesis," which is described as a theory that nutritional and environmental factors during an organism's developmental stages may have repercussions for the onset of chronic diseases later in life. As such, the study of epigenetics supports not only understanding the actual changes to genes based on the environment, but also the potential to use these changes as biomarkers for exposure to specific stressors and/or the likelihood of developing disease, and, going even further, as targets for preventing or treating the disease. One interesting idea postulated by the authors is that epigenetics may help to account in some degree for the variability of effects observed in studies of exposure to chemical contaminants in natural populations over time and by individual.
The authors also discuss heritability of epigenetic marks. Heritability implies that exposures leading to epigenetic marks in a parent might lead to the inheritance of epigenetic marks by future generations. In this aspect, epigenetics differs significantly from traditional ecotoxicology in that effects are postulated to be caused by past generations' exposures. Interesting avenues for future research could include work to further substantiate the heritability of epigenetic markers, and work to advance our understanding of intergenerational effects. One conclusion reached by the authors in their review of papers to date is that the mechanism for epigenetic inheritance seems to be consistent for vertebrates but much less so for invertebrates, suggesting that studies of the latter might be an area ripe for exploration in the future.
Another avenue suggested for study is how epigenetic effects are evinced for exposures that occur in the natural environment as opposed to laboratory conditions. The authors note that to date most epigenetics research has been carried out in laboratory environments as in vitro studies or using traditional laboratory test organisms, but that studies that have considered ecologically relevant organisms have found evidence of epigenetic effects.
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