Belgian team discovers role of oestrogen in development of male brain
New research by scientists in Belgium has proven that oestrogen, the quintessentially female hormone, plays a key role in determining masculine behaviour in mice. A team from the University of Liège, led by neuroscientist Julie Bakker, showed that female mice exhibited markedly male behaviour after oestrogen was allowed to penetrate their brains during development. It had long been known that a particular protein - alpha-fetoprotein (AFP) - plays a key role in mouse brain development by binding to oestrogen. However, it was unclear whether AFP facilitates the development of female brains by carrying the hormone, or by blocking it from entering the brain. In order to find out, the team took genetically modified female mice incapable of producing AFP and observed them in an environment with a sexually active male. Unlike normal female mice, the AFP-deficient animals showed little interest in the male, and tests showed that their brains contained fewer cells devoted to producing chemicals critical to reproduction, similar to male mice. Furthermore, when placed in a cage with a sexually receptive female, the AFP-deficient females mimicked the natural behaviour of male mice by attempting to mate with the lone female. However, in order to discover whether AFP causes female mice to behave like females by blocking oestrogen from the brain, the team prevented AFP-deficient mice from being exposed to the hormone whilst in the womb. The researchers found that with no exposure to AFP or oestrogen during brain development, the genetically modified mice behaved exactly like normal females. Therefore, not only do the results prove that it is the lack of oestrogen that makes the brains of female mice feminine, and that AFP plays the key role in blocking oestrogen from entering the brain; they also suggest that the presence of the hormone in the brain is what makes male mice behave like males. In humans and other primates, androgen, rather than oestrogen, plays the key role in making men's brains masculine. But Dr Bakker believes that sex hormone binding globulin (SHBG) may play a similar role in humans to AFP in mice by keeping women feminine and allowing males to develop masculine behaviour.
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