Evolution and humans: passing stress (Evolution)

by David Turell , Friday, November 09, 2018, 20:18 (2204 days ago) @ David Turell

A study of male sperm indicates how it is done:

https://www.scientificamerican.com/article/how-dads-stresses-get-passed-along-to-offspr...

"A stressed-out and traumatized father can leave scars in his children. New research suggests this happens because sperm “learn” paternal experiences via a mysterious mode of intercellular communication in which small blebs break off one cell and fuse with another.

"Carrying proteins, lipids and nucleic acids, these particles ejected from a cell act like a postal system that extends to all parts of the body, releasing little packages known as extracellular vesicles. Their contents seem carefully chosen. “The cargo inside the vesicle determines not just where it came from but where it’s going and what it’s doing when it gets there,” says Tracy Bale.

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"Striking evidence that harsh conditions affect a man’s children came from crop failures and war ravaging Europe more than a century ago. In those unplanned human experiments, prolonged famine appeared to set off a host of health changes in future generations, including higher cholesterol levels and increased rates of obesity and diabetes.

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"The big question is how information about the paternal environment reaches the womb in the first place. After all, Morgan says, the “dad is only in there for one night, perhaps just a few hours.” Could his sperm carry memories of prior trauma? The idea seemed reasonable yet controversial. Because DNA is packed so tightly in the nucleus of a sperm cell, “the thought that [the cell] would respond to anything in the environment really boggled people’s minds,” says Jennifer Chan, a former PhD student in Bale’s lab who’s now a postdoc at Icahn School of Medicine at Mount Sinai in New York City.

"Rather, there must be some other kind of cell whose DNA does react to environmental changes—and that cell, she reasoned, could then relay that information to sperm cells to transmit at fertilization. She focused on a population of cells that interact with developing sperm by releasing molecules that help sperm grow and mature. They also secrete extracellular vesicles—and Chan showed it is these vesicles whose contents fuse with sperm cells, instilling memories of dad’s prior stress.

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"The pups from nonstressed zygotes developed normally. Pups from stress-exposed zygotes, however, showed the same abnormal stress response as those whose dads had experienced stress before mating. That showed extracellular vesicles act as the conduit for transmitting paternal stress signals to the offspring, Chan says.

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"As a first step toward translating the findings to people, Morgan is collaborating with University of Pennsylvania psychiatrist Neill Epperson to track protein and RNA changes in human sperm samples. At the neuroscience meeting, Morgan presented data from a six-month study of 20 undergraduate and graduate students. Each month the participants came in and gave a sperm donation. They also completed a same-day survey asking how stressed they were feeling. Preliminary data suggests just several months after a student reports stress, his sperm shows changes in “small noncoding RNAs”—RNA molecules that do not get translated to protein but instead control which genes get turned on or off."

Comment: What happens in mice probably translates to humans. Historical evidence strongly suggests this. Epigenetic effects.