Epigenetics: Revolutionary New Spin on Nature Versus Nurture
by Sarah (Steve) Mosko, PhD
Appeared in: Surf City Voice, 05 Jan 2012
What if chemicals your great-great grandmother was exposed to, or even her diet, could affect your risk of falling victim to cancers, mental illness or Alzheimer’s disease? Sounds far-fetched perhaps, but what we are learning about the new science of epigenetics says it’s very possible and happens without a change to the DNA you inherited from her.
Epigenetics also explains how it is that your brain and toe are made of cells with identical DNA, but look and function so differently, and why identical twins are never exact replicas, though their DNA is.
The basis for all these phenomena lies not in the genome – the DNA sequences which make up our genes – but rather in intricate cell machinery sitting atop the DNA that dictates which genes are turned on or off at any point in the life of both a single cell or an entire organism, like a human being. A good analogy would be the orchestra conductor signaling when each instrument should play and how loudly. The Greek prefix “epi” means “on top of” or “in addition to,” hence the epigenome denotes the apparatus attached to the genome within a cell’s nucleus which enables tissues and even whole organisms with identical DNA to look and function very differently.
It’s long been appreciated that the epigenome is what coordinates the development of a fetus, telling an undifferentiated stem cell, for example, to morph into a heart cell at the right time. Because the epigenome is replicated along with the DNA during cell division, it also provides the “cell memory” needed so the instructions for making heart cells get passed on.
However, what’s new and creating shockwaves in our understanding of human illnesses is that the epigenome is influenced throughout our lifetime by not only normal internal factors, such as hormones, but by external ones too, like diet, drugs, stress and environmental pollutants. An epigenome that can adjust to changes in environmental conditions, like a scarcity of food, is advantageous if the adjustments enable you to adapt better to the environment. However, a non-fixed epigenome also means that conditions you were exposed to early in development which modified the epigenome in unfortunate ways might trigger diseases cropping up even decades later in adulthood.
Moreover, where we used to assume that any acquired epigenetic changes were erased during the type of cell division that produces eggs and sperm, we know now that eggs and sperm can also retain acquired epigenetic markings which, good or bad, can be passed on to your children and your children’s children.