Saturday, March 21, 2009

Can your environment change your genetic code?

Before I start, allow me to apologize about today’s slightly morbid study. While this blog entry will have to do with child abuse and suicide, bear with me, it will also reveal an interesting contribution to the age-old question of nature versus nurture. What makes you who you are? Is it your genes? Is it your environment? Some will say it’s your genes: I have green eyes because of my genes, and I am unfortunately neither tall nor blonde because of my stupid genes. Others say it’s your environment: I am able to speak French and English because of my family and geographical environments, and I have an obsession with sugary cereal because when I was growing up my older siblings always go to the box before I got a chance to (also, they happen to be magically delicious!). In reality, it’s a combination of both, and to complicate things a little, sometimes the environment messes with your genes, as beautifully demonstrated in a recent article published in the journal Nature Neuroscience.

In the article, a team of researchers from Montréal studied the effects of child abuse on the brain by comparing human brains from 3 different groups. Subjects in the first group had suffered from child abuse and later committed suicide. Subjects in the second group had not suffered from child abuse and committed suicide. Finally, subjects in the third group had not suffered from child abuse and died in an accident (as the study required human brains, sadly the tragic ends were necessary).

The first thing the researchers looked at was how much a gene called NR3C1 was activated in those brains. Genes are small segments of DNA that contain a code (a recipe) for a given protein. When they are active (or “expressed”), the machinery in your cells is reading the recipe and making the proteins. In this case, the gene NR3C1 is the recipe for a protein called glucocorticoid receptor. The glucocorticoid receptor is involved in many body functions, but the researchers in this study are especially interested in the fact that this receptor is an important player in how your body handles stress.

As it turns out, the brains of the subjects who had suffered from child abuse had significantly lower expression of the NR3C1 gene, and therefore fewer glucocorticoid receptors, than subjects from the two other groups. Since all the subjects in all the groups have the same NR3C1 gene, the researchers then set out to investigate why, if you suffered childhood abuse, would your machinery not read the NR3C1 recipe and make as much of the receptor. They showed that this is due to epigenetics (where epi means in addition to). Epigenetics happen when there are changes to the activation of a gene that is not due to a change in the gene’s recipe. In this case, certain parts of the NR3C1 gene are susceptible to a change called methylation, which essentially means sticking a bunch of methyl groups (close relatives to methane) right onto the recipe. These stickers prevent the machinery from reading the recipe, and so less glucocorticoid receptors can be made. Since those receptors are involved in how your body handles stress, if you have less of them, then presumably your body won’t be able to handle stress as well.

In summary, the take-home message of this article is that the environment, in this case childhood abuse, can influence how your genes are expressed, and that can shape who you are, for example how well you handle stress. It’s no surprise that kids that experience childhood adversity are more likely to display suicidal behaviors.

Now it had already been shown in animals that how well the mother cares for the offspring can influence how the offspring handle stress, so that’s not a complete shocker, but it’s nice to see an explanation of the mechanism for this and it’s also nice to see this confirmed in humans. I recently saw a talk from Dr Sydney Brenner, a Nobel Prize recipient in physiology and medicine, and he thought we should quit bugging our little furry friends and start experimenting on ourselves. Now there’s an ethical debate for another day, but once in a while, it’s nice to see that research in animals can be relevant to humans.

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