A GENE has been discovered that appears to dictate the sexual preferences of female mice. Delete the gene and the modified mice reject the advances of the males and attempt to mate with other females instead.
While it is impossible to say whether the finding has any relevance for human sexuality, it provides a clue as to how sexuality develops in mammals.
and colleagues at the Korea Advanced Institute of Science and Technology in Daejon, South Korea, deleted the FucM gene in mouse embryos to see what effect it would have on behaviour.
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Female mice lacking the gene avoided the advances of males, stopped sniffing male urine and attempted to mate with other females, though their ability to have pups was unaffected (BMC Genetics, ).
The gene the team deleted is for an enzyme called fucose mutarotase, which adds the sugar fucose to proteins. Park believes that disabling the gene exposes parts of the developing mouse brain linked with sexual preference in adult life to extra oestrogen. The hormone masculinises the brain in mice 鈥� though not in people.
In a normal female mouse fetus, this extra oestrogen would be 鈥渇iltered out鈥� by a substance called alpha-fetoprotein. But AFP only functions properly when adorned with fucose. So without the gene that makes the enzyme, AFP cannot keep the flood of oestrogen at bay.
As a result, the female mouse brain develops as if it were a male. 鈥淭he mutant female mouse underwent a slightly altered developmental program in the brain to resemble the male brain in terms of sexual preference,鈥� says Park.
Supporting the claim, Park鈥檚 team also report finding lower than usual concentrations of fucose-laden AFP in a female mouse embryo missing the crucial gene.
The results also make sense in light of the experiments in 2006 by Julie Bakker of the University of Li猫ge in Belgium, who found that when the gene for AFP was deleted.
Now, Park and his colleagues are hoping to use gene screening studies to find out whether fucose mutarotase has any association with sexual orientation in humans. He admits this research may be 鈥渧ery difficult鈥�, partly because it will not be easy to find a suitable number of volunteers.
, who researches the origins of sexuality, says that the Korean study is not directly relevant to the issue of human sexual orientation. As he points out, it is testosterone not oestrogen that masculinises the human brain, and human AFP doesn鈥檛 prevent oestrogen from entering the brain as it does in mice.
鈥淣evertheless, it is probably only a matter of time before molecular geneticists identify genes that influence sexual orientation in humans,鈥� says LeVay.
