Doublesex gene puts sex on the brain of fruitflies

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At first glance, the differences between males and females seem obvious, since genitalia, morphology, and courtship behavior often vary greatly between the two sexes. However, the biological mechanisms that create these sex differences are still poorly understood in many species. A new study in Nature Neuroscience looks into how the gene doublesex (dsx) may help wire sex differences into the brain of the fruitfly Drosophila melanogaster.

Using a marker that targets dsx-expressing cells, researchers were able to determine that it is expressed in many body tissues that are physically different in males and females. Furthermore, by manipulating dsx expression, they could alter the flies' morphological development; overexpression of the female-specific dsx isoform created males that outwardly resembled females, and overexpression of the male-specific isoform created highly masculinized females.

The researchers also show that dsx expression has significant effects on the structure of flies' brains. The brains of male and female fruit flies differ in neuronal numbers, axonal projections, synaptic densities, and the directionality of neural pathways. A previously identified gene called fruitless (fru)helps establish the full set of dsx-expressing neurons, and dsx dictates their specific sexual identity. These dsx-expressing neurons dictate courtship behavior in both male and female fruit flies. Inhibiting dsx expression severely affected both males' and females' courtship behavior, reduced following behavior and song production in males, and caused females to reject potential mates and resist copulation.

dsx is part of a group of genes which are highly conserved across species. Since dsx plays an important role in shaping sex-specific physiological, neural, and behavioral differences in fruit flies, it’s likely that these genes play important roles in the development of a wide variety of other species.

Nature Neuroscience, 2010. DOI: 10.1038/nn.2515 (About DOIs).

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