Genetic discrepancies between males and females measured mid-term.

21 October 2003

HELEN PEARSON

The activity of 51 genes is different in male and female mouse embryo brains. © Digital Vision

Genes drive the brains of male and female embryos apart as early as midway through gestation, a new study suggests¹. These gender differences were assumed to arise around birth due to hormones pumped out by males' budding testes.

Halfway into a mouse pregnancy, before the testes have even formed, the activity of 51 genes is different in males and females, says Eric Vilain of the University of California, Los Angeles. His team analysed 12,000 brain genes.

The discovery hints that unknown genes hardwire our gender - perhaps influencing the way that men and women think, tackle problems or perceive themselves.

"It's an indication of differences really, really early on," says Vilain.

"It shows up genes you'd never have thought of," says Bruce McEwen, who studies brain development at Rockefeller University in New York. "It's very provocative."

Sex on the brain

Everyone agrees that hormones mould the brain. In rats, testosterone oozed by the growing testes travels to the head and lays down circuits that lead to male patterns of behaviour, such as mating manners.

Vilain's team is not the first to find that genes also shape the brain's sexual development. In 1991, for example, researchers found that nerve cells from female rat brains, when grown in a dish, pump out more of a key enzyme than cells from males. "This idea has been coming through for a few years," says Glenda Gillies of Imperial College, London, who studies the effects of hormones on the brain.

But Vilain's study is the first to measure how many genetic differences there are, and to reveal that they occur in such young embryos. The team has not yet figured out what the 51 genes do - they might guide sprouting neurons to alternative connections, for example.

Vilain speculates that the brains of males who feel that they are female, or vice versa, may have a pattern of gene activity that resembles that of the opposite sex. "These individuals might be partly explained by gene differences in the brain," he says.

Such ideas are controversial. McEwen believes that the perception of our sex is probably imprinted first by genes and hormones, and then etched deeper by experiences during life, such as whether we act male or female, and whether we are treated as such. "I don't think it's an 'either/or'," he cautions.

1. Dewing, P., Shi, T., Horvath, S. & Vilain, E. Sexually dimorphic gene expression in mouse brain precedes gonadal differentiation. Molecular Brain Research, 118, 82 - 90, doi:10.1016/S0169-328X(03)00339-5 (2003). |Article|

(From:nature science update )