Scientists have discovered that a father’s sperm cells “learn” paternal experiences which are then passed on to children, according to Scientific American.
Sperm cells are capable of a mysterious form of intercellular communication in which small blebs break off of one cell and fuse with another. These particles carry proteins, lipids, and nucleic acids and act as a sort of postal system for the rest of the body, releasing small packages in the form of extracellular vesicles. The cellular information in these vesicles carry not only where it came from, but also where the vesicle is going and what it is to do when it gets there. These extracellular vesicles can alter sperm cells, among many other functions.
Tracy Bale, a neurobiologist at the University of Maryland School of Medicine, presented these findings at the annual meeting of the Society of Neuroscience in San Diego. The study was prompted by unplanned human experiments from over a century ago, when a long famine appeared to result in a host of health changes in future generations that suffered from higher cholesterol and higher rates of diabetes and obesity. Bale and her colleagues thought that there may be a genetic link to the phenomenon.
To test the hypothesis, Bale and her team created a series of experiments involving mice. Mice have intense stress reactions, resulting in spiking stress hormones. In the testing group, one generation of mice were exposed to a stressor, then their progeny were exposed to the same stressor. The researchers found that mice from male parents who had experienced the stressor reacted differently to it than mice whose male parent did not. Somehow, the brain was developing differently.
The fact that only the progeny of male parents experienced the changes sharply limited the possibilities. However, the idea that the phenomenon was transmitted through sperm cells seemed questionable at best, as DNA in those cells is packed so tightly that the possibility of it responding to the environment seemed prohibitive. Jennifer Chan, a postdoctorate student at the Icahn School of Medicine at Mount Sinai in New York City, focused on cells that do respond to environmental changes that might react with sperm cells. She focused her attention on a group of cells that interact with developing sperm to help them grow and mature, and found that the cells secreted extracellular vesicles that then fused with the sperm cells.
The findings were verified in another experiment, in which sperm from a non-stressed male was divided into two petri dishes. One was left as is, while the other dish was exposed to stress hormones. Chan then injected sperm cells from each batch into the eggs from a non-stressed female. Those fertilized eggs were then implanted into the same female. The researchers discovered that the mice from the stress-hormone batch featured abnormal reactions to a stressor, while the mice from the normal batch did not.
The findings are “novel and of very high impact, especially when we consider the impact of military service or other work environments that can confer high stress,” says Robert Rissman, a neuroscientist at the University of California at San Diego.