Environmental epigenetics is a branch of epigenetics that studies the influence of external environmental factors on the gene expression of a developing embryo. The way that genes are expressed may be passed down from parent to offspring through epigenetic modifications, although environmental influences do not alter the genome itself.
During embryonic development, epigenetic modifications determine which genes are expressed, which in turn determines the embryo's phenotype. When the offspring is still developing, genes can be turned on and off depending on exposure to certain environmental factors. While certain genes being turned on or off can increase the risk of developmental diseases or abnormal phenotypes, there is also the possibility that the phenotype will be non-functional. Environmental influence on epigenetics is highly variable, but certain environmental factors can greatly increase the risk of detrimental diseases being expressed at both early and adult life stages.
Environmental triggers for epigenetic change
The way that genes are expressed is influenced by the environment that the genome is in. These environmental influences are referred to as triggers and can involve anything that influences normal gene expression. How the genome is expressed depends on the environmental factors present during gestation. It is possible for the environmental effects of epigenetics to be deleterious or to be a natural part of the development pathway. When these environmental factors are detrimental it causes the deactivation of some DNA sequences, which can lead to atypical phenotypes. Some of the most common triggers include diet, temperature, exposure to harmful substances, and lifestyle. These triggers can cause low birth weight, neurological disorders, cancers, autoimmune diseases, and many other malformations.
These epigenetic triggers can change the way that an organism develops and have lifelong effects. Epigenetic changes can be passed down through offspring, present in multiple generations, and continue to change throughout a lifetime. Each sequence of affected DNA is not expressed at the same time. There are specific stages in which these expressions happen during development. The combined epigenetic mechanisms of DNA methylation and histone modification are responsible for how the genome is altered. For example, the suppression of oncogenes is regulated by DNA methylation and whether or not methylation is activated. This activation depends on the environment. When these activations happen, they can be passed down to the next generation through germ-cell differentiation.
Examples of triggers
Nutrients
Offspring can experience phenotypic changes depending on their access to nutrients. When nutrients are limited during pregnancy, the offspring's phenotypic expression can be disrupted. Nutrient intake is also important during lactation for the purpose of transferring nutrients to the offspring.
Exposures
Exposures to certain triggers such as alcohol or drugs can disrupt the normal expression of the offspring's phenotype. Antipsychotic drugs can lead to abnormal or stunted development during the fetal or embryonic stages.
Stress during pregnancy
When the maternal figure is exposed to stressors it can lead to a greater likelihood of expressing or stunting DNA expression. If the maternal figure experiences high levels of depression or stress it can lead to small litter sizes with lower birth rates. Decreased hormone production is the suspected cause of this.
Temperature
Changes in temperature can have varied effects on an organism. DNA methylation can be impacted by temperature when the temperature deviates from its normal value, preventing regular processes from taking place. Temperature can be considered a stressor in environmental epigenetics since it has the potential to change how offspring respond and react to their environment. Monarch butterflies are an example of how temperature can impact the survival and fitness of an organism. If exposed to stressors such as varying temperatures, these butterflies may express coloring that deviates from their normal color.