Evolution of neural sex-determination system in insects: insights from basal direct-developing insects

Abstract

Molecular and cellular basis of sexual dimorphism in the insect brain has been extensively studied in the fruit fly Drosophila melanogaster, an excellent model insect with powerful genetics. Studies in Drosophila have revealed that sexual dimorphism in the Drosophila brain is regulated under the control of the sex-specific splicing cascade and sex-specific gene products of two transcription factor genes, fruitless and doublesex. In the Drosophila brain, the neurons expressing either (or both) of the genes form sexually dimorphic circuits that regulate sex-specific behaviors. Recent studies on fruitless and doublesex homologs in basal direct-developing insects support the idea that the molecular mechanism underlying the formation of sexually dimorphic circuits in Drosophila is not ubiquitous in insects. In this review, I summarize the molecular basis of neural sex determination in Drosophila, and recent findings in the evolution of sex-determination genes in non-Drosophila insects.