Are We a Product of Our Genes or Our Environment?
Epigenetics: The Complex Interplay Between Nature and Nurture
Tomorrow, we have a podcast episode dropping on epigenetics — and it's a good one. So, we thought we'd queue up the conversation with a primer on epigenetics.
Have you ever wondered why identical twins, despite sharing the exact same DNA, can grow up to be so different? Or why some people seem to age faster than others, even when they're the same chronological age? The answers lie in a fascinating field of study called epigenetics, which is revolutionizing our understanding of how genes work and challenging long-held beliefs about nature versus nurture.
Epigenetics goes beyond the basic genetic code, exploring how genes are expressed and regulated. This field of study helps explain why cells with identical DNA can have vastly different functions in our bodies and how our environment and experiences can influence our genetic expression. As we delve into the world of epigenetics, we'll explore its significance in human biology, from its role in cellular differentiation to its impact on aging and disease. We'll also examine how this relatively new field is bridging the gap between our genetic blueprint and the influence of our environment, offering new perspectives on the age-old nature versus nurture debate.
Let's begin the discussion on epigenetics by explaining its place in the broader context of genetic science, starting with one of the most significant scientific achievements of our time…
The Human Genome Project and beyond
On April 14th, 2003, the International Human Genome Sequencing Consortium announced the successful completion of the Human Genome Project. This is widely considered to be one of the greatest achievements in biomedical science to date, because, in a little over a decade, scientists were able to collaboratively identify and sequence the 3 billion chemical base pairs that make up human DNA and map them to specific genes. However, there is so much more influencing our phenotypes (the unique set of physical traits and characteristics that make us who we are) than just this chemical blueprint. Enter epigenetics.
What is epigenetics?
Epigenetics directly translates to “on top of” or “above” genetics. Meaning, epigenetics represents information that is layered on top of our DNA that influences how the genes contained within them operate. This layered information is influenced by a number of things including environmental factors, lifestyle, and unique experiences. The perfect illustrative example of epigenetics at work is identical twins. Identical, or “monozygotic” twins, share the exact same DNA code, but, as anyone who has ever known a pair of twins can attest, they often exhibit very distinct differences in personality traits, health, and/or behavior. But why is that? If our genes make up who we are, then shouldn’t identical twins be, well, identical?
We love a good analogy.
To answer this question, we first have to review some basic biology… which means it’s time for an analogy! Think of your DNA as a library full of books that contain all the instructions for making a human. Each book represents a different gene that codes for a specific trait – whether that be height, eye color, or attached earlobes. We can consider epigenetic markers as bookmarks placed in specific parts of books to indicate which sections should be read or ignored. These bookmarks can be placed at any number of locations within a book and can either highlight a section to read (turn a gene on for expression) or cover up a section that can be skipped over (turn a gene off). Extending the analogy a bit further, book covers represent modifications to proteins called “histones,” which act as spools for the long, thin strands of our DNA to wrap around so it can fit inside a cell and doesn’t get all tangled and disorganized. Book covers can be soft or hard, making the books’ contents easier or harder to access. For instance, a stiff hardcover book is harder to open (genes are not accessible and thus turned off), while an old paperback cover is loose and easy to open (genes are accessible and turned on). When DNA is accessible, it means that it can be transcribed into RNA (an intermediary molecule), and then eventually translated into proteins, the functional unit of human biology.
Epigenetics in action
Most of the cells in the human body contain all 23 pairs of chromosomes that hold the potential information for creating any/all proteins. But these genes are not all going to be “turned on” for expression at the same time. Scientists estimate that there are around 200 different types of cells in the human body and each cell type has a distinct gene expression profile that defines its role. In other words, the specific set of genes turned on and off in a given cell that determines its identity and function. As an example, specialized cells located within the stomach called “parietal cells” secrete hydrochloric acid, a key ingredient of gastric acid necessary for facilitating digestion. The gene that encodes for the enzyme responsible for this process is called the ATP4A gene. This gene is silenced, or “turned off,” in our retinal cells because we would definitely NOT want our eyes secreting any amount of hydrochloric acid. Thanks, epigenetics!
Back to twins.
Let’s get back to the question of identical twins. Epigenetic marks are influenced by both the internal environment (i.e. determination of cellular identity) and the external environment. This is why identical twins can grow up to lead such different lives, both behaviorally and physiologically. An individual’s epigenome, the set of all the epigenetic markers interacting with DNA, mediates a lifelong dialogue between genes and the environment. Epigenetic markers that turn genes on and off can be mediated by lifestyle factors including diet, exercise, smoking, exposure to toxins, and medication. As twins get older, and interact with their environment in unique ways, their epigenomes diverge, which affects the way they age and their susceptibility to various diseases.
Epigenetics in disease and aging
An exciting new area of research is exploring the role of epigenetics in the developmental progression of a wide variety of diseases, providing insight into their origins and potential prevention mechanisms. For example:
In breast and prostate cancer, genes have been identified that are epigenetically silenced, contributing to the spread of cancer cells, tumor progression, and resistance to treatment.
In heart disease, epigenetic modifications have been linked to plaque buildup leading to heart attacks and strokes.
There is even evidence to support epigenetic regulation of specific genes in age-related neurological conditions such as Alzheimer's disease and dementia.
In fact, epigenetics is a key regulator of aging in general. As we age, patterns of gene expression change, which is partially why we experience changes in appearance (e.g., wrinkles), physical ability, and cognition throughout the lifespan. Scientists have even developed a way to estimate and predict biological aging trajectories based on a type of epigenetic mechanism called DNA methylation. These "epigenetic clocks" help to provide valuable insight into the physiological state of an individual since biological age can often differ from chronological age (the number of years a person has lived), and may even help to answer an enduring scientific question: why do we age?
Transgenerational epigenetic inheritance
An intriguing area of epigenetic research is transgenerational epigenetic inheritance. This concept suggests that some epigenetic changes can be passed down to offspring, potentially influencing their traits and disease susceptibilities. While still controversial and under intense study, this idea challenges our traditional understanding of inheritance and could have far-reaching implications for human health and evolution.
The future of epigenetics in medicine
The field of epigenetics is opening up new avenues for medical treatments. Epigenetic therapies are currently being developed for various cancers and other diseases. These treatments aim to reverse abnormal epigenetic modifications, potentially restoring normal gene function. Additionally, epigenetics is playing an increasingly important role in personalized medicine. By understanding an individual's epigenetic profile, doctors may be able to tailor treatments more effectively and even predict future health risks.
As research in epigenetics progresses, it may lead to new diagnostic tools and therapeutic approaches for various diseases. However, it's important to note that epigenetic testing is not yet commonplace in clinical practice. As this field advances, it will likely raise new ethical considerations regarding privacy, data interpretation, and the potential for discrimination based on epigenetic information.
Conclusion: Nature, nurture, and epigenetics
Ultimately, epigenetics helps to unify the age-old debate of “nature versus nurture.” Historically, the “nurture” theory stipulates that our environment dictates who we are and who we have the potential to become, while the “nature” theory specifies that genes, the unchangeable blueprint in you from birth, decide everything. So, are we a product of our genes or a product of our environment? Epigenetics says both. It is where nature and nurture interact, bridging the gap between our genetic code and our environment.
xoxo,
Team Unbiased Science
(Drs. Jess Steier and Sarah Scheinman)