For better or worse—and despite resolutions to the contrary—we all end up like our parents to some extent. Over time, I’ve noticed my thinking has become strangely familiar, as though I’ve heard it somewhere before…and then I realize I just thought or said something my dad would say. Just the other day, I realized that I sign my name exactly like my mom does, even though as a kid I used to complain that she trails off after writing the “R” of our last name. Genes work strange magic sometimes, conflating nurture and nature and working far deeper than the conventional inheritance of diseases or other health conditions. Researchers now believe that symptoms of trauma, once thought to be non-genetic responses, can actually be passed down via sperm.
Scientists have always wondered why descendants of trauma survivors are more inclined toward mental illness than the average person. Some have looked to genetic to explain it, but have come up empty. A new study in Nature Neuroscience suggests that trauma in early life can affect a mechanism that dictates gene expression, in mouse sperm. Trauma changes gene expression, which then has cascading biological effects. But what wasn’t clear is whether those changes could be passed down to future generations. The provocative question raises the possibility of the inheritance of non-genetic traits.
To shed light on the matter, a Swiss University ETH Zurich geneticist induced trauma in mice by separating baby male mice from their mothers at irregular intervals. While mothers can pass down trauma symptoms, the researchers were particularly interested in the males and what would happen when they bred. The stressed out mice displayed typical trauma responses—they were less fearful of lights and open space, and they exhibit depression (they ate pint after pint of Ben and Jerry’s). Their microRNAs, which control the expression of genes, but are themselves non-coding, became over-expressed, decreasing the production of key proteins. Essentially, these mice were pretty messed up.
But that’s not the interesting part. These traumatized baby male mice eventually mated and had their own offspring. The next generation exhibited the same symptoms as their fathers, even though they themselves hadn’t experienced trauma. And when those mice produced babies, the same symptoms existed, even though their microRNA levels were closer to normal. The key is the sperm of the traumatized mice, which contains high amounts of the microRNAs. Essentially, “early childhood trauma has consequences not only for the brain but also for the sperm cell line.”
The scientists also injected microRNAs from traumatized mice into the egg cells of females with the same result occurred. What researchers don’t understand is how microRNA changes move from the brain to sperm. They plan to study that link next. Suffice it to say that this research could change the way we think about the effects of trauma and how long it lasts. And, of course, the importance of choosing sperm carefully.