Most of our genes are expressed in pairs â€“ one copy inherited from each parent. But pairs of so-called imprinted genes have just one copy “switched on”.
However, it was recently discovered that maternal and paternal copies of the imprinted gene Grb10 may be switched on in different places in the body. To distinguish one copy from the other, Andrew Ward at the University of Bath, UK, and colleagues knocked out Grb10 in male mice and mated them with normal females. They found that the offspring â€“ which had only inherited the maternal copy of the gene â€“ expressed the gene in various parts of their bodies, but not their brains. The team then mated females lacking the gene with normal males, and found that their offspring, having inherited only the paternal copy, expressed the gene only in the brain and spinal cord.
Maternal Grb10 is known to restrict fetal growth. To find out what role the paternal gene might play, the team monitored the mice’s interactions. Mice lacking the paternal gene groomed their mates so much that the latter lost their whiskers and fur.
Ward’s team concludes that the presence of the paternal gene in the brain may act to moderate this “risky” social behaviour in mice. This is the first time an imprinted gene has been shown to have different functions, at different places in the body, says Ward.
Humans have the same gene, so there is a possibility that it might be influencing our own social behaviours, he adds.
“The most interesting human parallel is Silver-Russell syndrome,” says Gudrun Moore, a geneticist at University College London’s Institute of Child Health. Ten per cent of people with this growth disorder have two copies of a maternal chromosome and no copies from the father. “These individuals have not been tested for overtly dominant behaviour, though they do have speech delay, learning difficulties and lower IQ,” Moore says.