Epigenetics
Epigenetics refers to the study of changes in gene expression or cellular phenotype that do not involve alterations to the underlying DNA sequence. It involves modifications that affect how genes are turned on or off, and these changes can be influenced by various environmental factors.
The main epigenetic mechanisms include DNA methylation and histone-tail modifications. These processes can regulate gene expression by altering the chromatin structure, making genes more or less accessible for transcription.
Epigenetic modifications can have significant implications for health and disease. For example, aberrant DNA methylation patterns are recognized as a common hallmark of human tumors, often leading to the inactivation of tumor-suppressor genes.
Additionally, epigenetic mechanisms are involved in synaptic plasticity and are essential for learning and memory, with dysfunctions potentially contributing to neurodegenerative and psychiatric diseases. Epigenetic changes can be dynamic and reversible, offering potential therapeutic targets for various conditions.
You could look at genes as inherited metabolism, luckily it's very malleable.
Without considering gene expression, things would appear grim, a person would just be doomed by a random chance of genes they inherited.
"Cells have to, in some sense, perceive themselves and their environment, because their environment is an essential part of their existence, governing what they are and what they can become. To understand the nature of cellular perception, we have to look beyond existing descriptions of what cells are." - Ray Peat, 1998 newsletter, Cellular Judgments (Tissue Firmness and Elasticity).
Examples
1. DNA Methylation
This is a common epigenetic modification where a methyl group is added to the DNA molecule, typically at CpG sites. DNA methylation can lead to the inactivation of genes, such as tumor-suppressor genes in cancer, through hypermethylation of their promoter regions.
2. Histone Modification
Histones are proteins around which DNA is wrapped, and their modification can affect gene expression. For example, histone acetylation is associated with gene activation, while deacetylation is linked to gene repression.
The deregulation of histone acetylation has been implicated in cancer and neurodegenerative diseases.
3. Environmental Influence on Gene Expression
Environmental factors can lead to epigenetic changes. For instance, stress in the environment can cause changes in the chromosomes, as seen in the concept of "jumping genes" or transposable elements that can move within the genome in response to stress.
4. Epigenetic Regulation in Neurogenesis
In the adult mammalian brain, activity-dependent expression of genes critical for neurogenesis can be regulated by epigenetic mechanisms. For example, the stress response gene Gadd45b can be induced by neuronal activity, promoting neurogenesis through dynamic DNA demethylation.
5. Individual Differences in Behavior
Studies on genetically identical mice have shown that individual differences in behavior can arise due to nonshared environmental contributions, which are mediated by epigenetic changes affecting brain plasticity.
Identical twins - They start with the same DNA, but differences in diet, stress, or lifestyle can cause different patterns of gene expression, leading to differences in IQ even one developing a disease while the other does not.
Queen bee/worker bee
The differentiation between queen bees and worker bees is a fascinating example of epigenetics in action. Although queen bees and worker bees are genetically identical, they develop into distinct castes with different roles in the hive due to epigenetic modifications influenced by their environment, particularly their diet.
The primary factor that determines whether a female larva will develop into a queen or a worker is the type of food it receives during its larval stage. Larvae destined to become queens are fed a substance called royal jelly, which is rich in nutrients and has a unique composition compared to the food given to worker larvae.
This diet triggers epigenetic changes that activate or silence specific genes, leading to the development of the physical and reproductive characteristics of a queen bee.
These epigenetic changes involve processes such as DNA methylation and histone modification, which alter gene expression without changing the underlying DNA sequence. In the case of queen bees, these modifications result in the development of fully functional ovaries and a larger body size,enabling them to reproduce and lead the hive.
This example illustrates how environmental factors, such as diet, can influence gene expression and lead to significant differences in phenotype, despite identical genetic information. It highlights the dynamic nature of gene expression and the role of epigenetics in development and differentiation.
Irish famine
Causing subsequent generatuin to store more fat
Height increase in Dutch
Once among the shortest peoples in Europe, the Dutch grew to become the tallest in the world thanks to improved nutrition, healthcare, and living conditions over the past two centuries.
Dutch Hunger Winter (1944–45)
Babies conceived during the famine showed higher risks of obesity, diabetes, and heart disease decades later, because their early malnutrition caused epigenetic changes that “programmed” their metabolism.
Parental stress effects
Studies in mice show that stressed fathers can pass down altered stress responses to their offspring via epigenetic changes in sperm.
