N.B. This science review was originally published in Optimyz Magazine in September 2011 by Mandy Wintink, PhD.
Inheriting Our Parents Life Experiences
Still wondering about the nature-nurture debate? It seems rather clear by now that what we end up as is an interaction between our genes and the environment in which we exist. One of the ways in which this interaction happens is through a phenomenon called ‘epigenetics’. Whereas genetics has to do with the structure of the DNA sequence that codes for our genes and is passed on from generation to the next, epigenetics has to do with genetic changes and inheritance that lie outside the DNA sequence and involves biochemical changes that affect the expression of genes.
Epigenetics is a sort of imprinting, whereby the environment leaves its footprints on the DNA. This happens through a process called “DNA methylation” (an addition of a methyl group to the DNA sequence) or “histone deacetylation” (a transfer of the acetyl group to Co-enzyme A). The consequence of these two mechanisms is a suppression in gene activity, or the reverse effect if DNA demethylation and histone acetylation occurs. In the former case, the DNA stays tightly wound and is less able to express itself resulting in a suppression, whereas during the latter case, the DNA loosens and is more free to express itself resulting in heightened gene expression. What’s really interesting about epigenetics is that these changes can also be passed on to the next generation, providing a biological mechanism for a parent to pass on life experience.
How we respond to early life experiences is a great example of some current epigenetic research. Montreal researcher Michael Meaney has been using a rat maternal care model to investigate this. He has shown that when rat pups receive good maternal care (i.e., lots of licking, grooming, and nursing) they grow up to be less fearful, show fewer signs of physiological stress, and, if female, provide better care for their young. He has also shown that these behaviours run in families. Having a good mom means that rats are more likely to be a good moms themselves and that her offspring are less fearful, show fewer signs of stress, and also become good moms.
These behaviours continue across generations unless of course, you’re swapped at birth! Meaney placed pups born to bad moms with good moms and vice versa. Surprisingly, the pups took on the behaviours associated with the maternal care they received, not the behaviours associated with the maternal care of their biological moms. What this meant was that the environment had a greater impact on how rats would turn out as adults than did the genetic lineage.
These results were so fascinating that they were published in the very prestigious journal, Science, in 1999. Then in 2004 Meaney’s group showed that these effects were happening epigenetically and were passed on to subsequent generations. They found changes in DNA methylation and histone deacetylation that were associated with both the rats’ early life experiences and the behaviours and physiology they developed in adulthood. And even though they changes were passed on, if they pups were swapped at birth, the effects were reversed, further confirming they were epigenetic and not just genetic.
Even more convincing of an epigenetic mode of inheritance, was when Meaney’s group chemically blocked the DNA methylation and histone deacetylation in the pups raised by bad moms. When they blocked these epigenetic changes the pups grew up to behave and show signs of stress as if they had been reared by good moms! This showed, without a doubt, that epigenetic changes were necessary for the early life experiences to dictate the future of the pups. And when those changes were blocked, the environment could not leave its footprints.