Fruitless specifies sexually dimorphic neural circuitry in the Drosophila brain

Sex on the Brian The fruitless gene in the fruit fly Drosophila was first identified because mutant males exhibit homosexual courtship. Its gene products, different in males and females, are found in groups of neurons throughout the central nervous system. No obvious neuroanatomical differences were known but now a cluster of fruitless-expressing brain cells that differs between males and females has been found. This difference is produced by the elimination of immature neuronal cells in females. Male-specific Fru protein inhibits this programmed cell death, allowing the formation of a neural circuit that directs males to court females and not males. This shows how one gene can direct brain development and sex-specific behaviour. On this framework, sexual orientation can be understood in relation to an identified neuronal circuit and defined actions of the sex determination gene. The cover shows the male-specific neurons.