Epigenetics

Epigenetics Overview

Definition of Epigenetics

Epigenetics refers to the mechanisms that control gene function without altering the underlying DNA structure. According to Puumala & Hoyme (2015), epigenetics is defined as "changes in gene function that do not alter its underlying structure of DNA but result in genes being switched on or off in a reversible way" (p. 15). David Moore elaborates by stating it is "how genetic material is activated or deactivated—that is, expressed—in different contexts" (Moore, 2015, p. 14). This indicates that alongside inheriting DNA from our parents, we also inherit a variety of chemical markers that regulate gene activity, determining whether genes are expressed and how much protein they produce.

Genetic Activation and Cell Differentiation

  • Every cell within an organism possesses the same DNA; however, only specific genes are expressed at any given time. For instance, while all cells contain the necessary genetic information to develop an eye, this potential is only realized in appropriate cells. The mechanisms governing this selective activation are epigenetic.

Mechanisms of Epigenetics

DNA Methylation

  • The most well-studied mechanism of epigenetics is DNA methylation, involving the addition of methyl groups (CH) to nucleic acids.

  • Methylation influences the gene's ability to produce proteins without changing the genetic code itself. Generally, genes with high levels of methylation are silenced or "turned off" (Moore, 2015).

  • Regulation of DNA methylation is observed to be similar across individuals, indicating a level of conservation in this process among species.

  • During early development, genes responsible for specific functions—like eye development—become methylated and inactive in all tissues except those destined to develop as eyes.

Experience and Epigenetic Modification

  • Epigenetic effects can also be influenced by individual experiences. For example, studies have shown that experiences such as stress during pregnancy can lead to long-lasting epigenetic modifications in offspring.

  • A notable study examined the effects of the 1998 Quebec ice storm on pregnant women. Thirteen years later, their children's immune system cells exhibited varied levels of DNA methylation linked to the mothers' experiences of hardship (Cao-Lei et al., 2014).

  • In another study, children aged 11 to 14 who had experienced physical maltreatment exhibited increased methylation in genes associated with stress response and nerve growth factors compared to their non-maltreated peers (Romens et al., 2015).

  • Further research has connected early life stress to changes in genes that govern cortisol, a key stress hormone, impacting behaviors later in life (Kertes et al., 2016; Parades et al., 2016).

  • The implications of these findings suggest that early adverse experiences could either enhance adaptability in challenging environments or increase vulnerability to mental and physical health disorders.

Transgenerational Epigenetic Effects

  • Research in animals has demonstrated that epigenetic markers, particularly those resulting from maternal behaviors, can be inherited across generations.

  • For instance, mother rats that groom their pups create a pattern of behavior where their offspring mimic similar grooming styles, regardless of their biological mother's behavior (Francis et al., 1999; Meaney, 2010, 2013). This suggests that stress responses may be transmitted chemically rather than genetically.

  • In humans, excessive childhood stress linked to abuse or neglect correlates with mental health issues later in life, implicating genetic interactions in response to environmental stressors (Cicchetti & Toth, 2006; Carpenter et al., 2004; Lee et al., 2005).

  • Current methodologies for observing chemical traces in humans are limited, yet studies suggest that stress adaptation mechanisms involving cortisol and brain processes are likely regulated by epigenetic factors (Moore, 2015).

Historical Epigenetic Evidence

  • Although direct evidence for the heritability of behaviors through epigenetics is scarce in humans, important findings regarding physical aspects emerge from the Dutch Hunger Winter during WWII. Pregnant women who experienced famine not only affected their health but also the health of their children and grandchildren.

  • Children conceived during this famine displayed a higher risk for obesity, with subsequent generations also demonstrating similar traits. These results underscore the impact of maternal malnutrition during pregnancy on future generations (Lumey, 1998). A similar occurrence was reported in Swedish men regarding malnutrition effects on health (Kaati et al., 2002).

Conclusion

The exploration of epigenetics is still evolving, with ongoing research promising to clarify the biological underpinnings of inheritance, as well as elucidate the complex interactions between genes and environmental factors that influence phenotypes across generations.