Scientists discover genetic ‘switch’ in mice that turns caring fathers into violent beasts

At least in African striped rats, flipping a single gene switch can cause doting fathers to attack their offspring, a new study suggests. But genes themselves aren’t the only thing responsible for this switch from careful paternal behavior to aggressive paternity. Social conditions also influenced the behavior of male mice.

The discovery could shed more light on the genetic mechanisms by which some mammals act as caring fathers while others abandon their young. Active paternity is rare among mammals, with only 5% of the 6,000 species of mammals having fathers. For this reason, scientists know far less about how paternal care works in mammals than they do about maternal care in mammals. African striped rats (Rhabdomys pumilio) are useful for studying mammalian paternal care, as males display a wide range of behaviors toward their pups, including huddled together to keep warm and actively ignoring their offspring.

In a study published February 18 in the journal Nature, researchers placed male African striped mice in cages alone with a group of pups or in group cages with other fathers and their pups. They found that males kept in groups were more likely to ignore or attempt to kill pups.

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To identify the brain regions that mediate this behavior, the researchers exposed male mice to pups and monitored their brain activity. They found that attentive fathers had more activity in one area of ​​the brain called the medial preoptic area (MPOA).

“Decades of research has shown that the MPOA functions as a hub for maternal care across mammals,” lead author and postdoctoral researcher Forrest Rogers, Ph.D., a researcher at the Princeton Neuroscience Institute, told Live Science via email.

The team then dissected the mouse brains and measured gene activity in cells in the MPOA. The researchers found that a gene called agouti was more active in males that attacked puppies than in males that cared for them.

“Aguti is well known for its role in skin pigmentation and metabolism, so it was exciting to discover a previously unknown role in the brain in parenting behavior,” Rogers said in a statement.

To confirm that agouti expression is involved in the transition between alert and aggressive behavior, the researchers first exposed mice to pups and then injected them with a virus that enhances agouti gene expression in MPOA. When the males were exposed to the pups again, their behavior changed.

“We found that as agouti increases, these males become more aggressive toward their pups,” Rogers told Live Science in an email, suggesting that the gene acts as a kind of “switch” that toggles between aggressive and considerate behavior in the father mice.

The agouti gene found within MPOA may be strongly associated with changes in paternal care, but Rogers cautioned that this molecular switch is not the whole story.

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“Indeed, for some striped mice, increased agouti expression appears to be sufficient to induce infanticide,” he said. “However, we also found that there are other factors that may also moderate this effect, for example current social housing.”

When the researchers moved the males from group housing to single cages, agouti levels decreased and there were more caregivers, suggesting the gene is influenced by social context rather than food availability.

The study may have uncovered the possibility of a genetic switch for fatherhood, but it also had important limitations. Of note, only male African striped mice were studied. And although fathering behavior differed within the species, the researchers cautioned against extrapolating their findings to other species.

“While we do not exclude the possibility that agouti functions similarly in other species (such as humans), there is currently no evidence to suggest this specific function in humans (or other mammals),” Rogers said in an email to LiveScience.