Drosophila have male and female brain cells of different shapes, and the sex difference is determined by whether these cells have (male) or not (female) "maleized substances".However, it was unclear why "male substances" maleized the shape of brain cells, and in females without "male substances", brain cells became female shapes.

　The gene fruitless synthesizes the Fruitless protein in cells in the male brain, but not in the female brain, creating a gender difference in the brain. Among Fruitless cells, the cell group called mAL has a gender difference of extending protrusions in 3 places in males and 2 places in females.This time, we observed changes in the shape of nerve cells by artificially inhibiting the genes used when nerves stretch their protrusions one by one.As a result, it was discovered that when the function of the Robo gene is reduced, male-specific protrusions also occur in the female brain.This also revealed the code of DNA that the Fruitless protein uses as a marker for binding partners.The code is a base sequence with a 16-character palindromic structure, and when a Fruitless protein binds to a Robo gene with this structure, the function of the Robo gene is suppressed.When this structure was removed from the Robo gene, male mAL cells were unable to extend male-specific protrusions and courtship behavior became abnormal.In this way, the mechanism by which gender differences occur in the brain was elucidated from the genetic code.

　Once all the target genes for the Fruitless protein have been elucidated, the causes of gender differences in the brain and behavioral differences between males and females will be clarified.The Robo gene is also present in humans, and it is interesting to see if the human brain also acquires gender differences by the same mechanism.