Investigating Molecular And Neuronal Mechanisms Of How The Sex Determination Gene Doublesex Regulates Sexually Dimorphic Behaviors In Drosophila

Most animal species display sexually dimorphic behaviors.Studying how sexually dimorphic behaviors are established is crucial for understanding biodiversity and behavioral evolution across animal species.doublesex（dsx）was first identified in Drosophila melanogaster as a member of Dmrt（Doublesex/Mab-3 related transcription factor）gene family.dsx mutants display intersexual phenotypes,with intermediate sexual traits between males and females.dsx encodes transcription factor Dsx^F in females and Dsx^M in males,which are responsible for sex differentiation in flies and other insects.However,whether and how neuronal Dsx proteins control sexually dimorphic behaviors remain poorly understood.In this study,we discover that neuronal dsx is crucial for reproductive and aggressive behaviors in both Drosophila males and females.Knocking down dsx^Mexpression in the male brain decreases male courtship and aggression,whereas knocking down dsx^F expression in the female brain decreases female receptivity but enhances female aggression.Furthermore,knocking down or overexpressing dsx^Mexpression in～8 pairs of male-specific P1^a neurons decreases or enhances male aggression,respectively;while knocking down dsx^F expression in～2 pairs of female-specific p C1^d neurons increases female aggression.We further show that Dsx functions both developmentally and acutely in these sex-specific interneurons to control sexually dimorphic behaviors.In mammals,dsx-related Dmrt genes direct the differentiation of gonads that produce sex hormones controlling both the organization and activation of neural circuits underlying sexually dimorphic behaviors.In this study,we find that sex-specific Dsx isoforms promote distinct sexual behaviors in both sexes,and oppositely regulate aggression to establish male-biased aggressiveness.These results reveal how a conserved sex-determination gene plays both organizational and activational roles in sexually dimorphic behaviors.In addition,we identify a novel male-specific dsx ^M2 transcript,which has a potentially masculinizing function like dsx^M.We find that the dsx ^M2 transcript exists in a variety of insect species from flies to cockroaches,and is generated through intron retention-induced sex-specific splicing.We propose an evolutionary pathway of alternative splicing of dsx,from the transcription-based mechanisms in vertebrates and worms to the splicing-based mechanisms in insects.These results broaden our understanding of the molecular mechanisms underlying sexual differentiation and sexually dimorphic behaviors.