Regulation by male-specific fruitless of neural circuitry used during courtship and copulation behavior in Drosophila melanogaster

Graduation date: 2006Courtship and copulation behaviors in Drosophila melanogaster males are\ud regulated by sex-specific products from the gene fruitless (fru). Male-specific FRU\ud proteins (FRU[superscript M]) are putative transcription factors of the BTB-ZnF family that likely\ud act by controlling development and maintenance of the neural circuitry used during\ud male sexual behavior. However, which neuronal characteristics are regulated by\ud FRU[superscript M] is mostly unknown and how FRU[superscript M] neurons are grouped into circuits and the\ud role that specific neuronal circuits play in sexual behavior has not been elucidated. I\ud have identified a subset of FRU[superscript M] neurons that co-express the transcription factor,\ud Engrailed (En). After fru[superscript M]-RNAi-induced targeted removal of FRU[superscript M] proteins from\ud FRU[superscript M]/En neurons, males were impaired in their ability to initiate or maintain\ud copulation. Further, I examined two characteristics, the initial projections and\ud neurotransmitters used by FRU[superscript M]/En neurons. Males and females showed a difference\ud in the neurochemistry of FRU[superscript M]/En neurons in the thoracic ganglia; this\ud neurochemistry is disrupted in fru mutant males.\ud For one cohort of serotonergic neurons in the abdominal ganglion that were\ud previously shown to be dependent on FRU[superscript M] for expression of serotonin, I determined\ud that FRU[superscript M] works in conjunction with other sex-specific genes, TAKEOUT (TO) and\ud DOUBLESEX (DSX), to induce of serotonin expression in males; in females\ud serotonin expression is repressed by DSX and TO.\ud Finally, I performed a genetic screen for genes that interact with, or are\ud downstream targets of, fru, dsx, or dissatisfaction (dsf). I assessed fertility, copulation\ud success, and abdominal muscle development of EMS-mutagenized flies, resulting in\ud one fly line in which homozygous mutant animals had a novel muscle phenotype. By\ud genetic tests, the mutation was found to be allelic to string, which encodes a Cdc25-\ud like phosphatase.\ud Taken together, my research demonstrates that subsets of FRU[superscript M] neurons\ud function in circumscribed circuits to regulate specific portions of sexual behavior, and\ud that FRU[superscript M], along with other sex-specific genes, controls development of these\ud neurons in part by determining neurochemistry. Further, FRU[superscript M] likely directs multiple\ud downstream targets, in different subsets of neurons in which it is expressed, which\ud collectively provide correct development of neural circuits underlying courtship and\ud copulation behavior