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"There are diseases such as bipolar disorder, that run in families but can't be traced back to a particular gene," Dr. Mansuy said. The mechanism of transmission for this non-genetic inheritance are, the scientists surmise, short ribonucleic acid (RNA) molecules, which are synthesized from deoxyribonucleic acid (DNA) by enzymes and are used to produce more RNA molecules.
In the experiment, Mansuy and her team separated young mice from their mothers in order to cause "unpredictable maternal separation combined with unpredictable maternal stress," or "MSUS mice." When the young MSUS mice reached adulthood, they were more likely than control mice to take risks, and exhibited an altered glucose metabolism, which suggested that the early trauma had caused permanent changes to the way in which the RNA within their cells functioned.
Those changes were not, however, confined to the present generation of MSUS mice. When they were bred with non-traumatized adults from the control group, the offspring also exhibited the altered glucose metabolism. To discover how such stress was passed on, Mansuy and her team extracted RNA from the sperm of MSUS mice and injected it into fertilized eggs that had been fertilized by DNA from control mice.
When those mice became adults, they exhibited the same metabolic and behavioral traits as the MSUS mice, despite not having been traumatized themselves.
The exact mechanism that alters the RNA's profile is still unclear, but Stephen Krawetz, the associate director of the C.S. Mott Center for Human Growth and Development at Wayne State University School of Medicine, said that it is "quite an exciting piece of work." He told The Scientist that "[w]hat it's doing is building on the notion that dad's contribution is actually more than just his genes when he fertilizes the oocyte."
"It really adds a new dimension in terms of what impact dad can have."
Comment: For more information read:
Psychological trauma may have cross-generational effects
Trauma can be inherited from parents