Article Abdominal-B Neurons Control Drosophila Virgin Female Receptivity

Howard Hughes Medical InstituteSummaryBackground: Female sexual receptivity offers an excellentmodel for complex behavioral decisions. The female mustparse her own reproductive state, the external environment,and male sensory cues to decide whether to copulate. Inthe fly Drosophila melanogaster, virgin female receptivity hasreceived relatively little attention, and its neural circuitry andindividual behavioral components remain unmapped. Usinga genome-wide neuronal RNAi screen, we identify a subpopu-lation of neurons responsible for pausing, a novel behavioralaspect of virgin female receptivity characterized in this study.Results: We show that Abdominal-B (Abd-B), a homeoboxtranscription factor, is required in developing neurons for highlevels of virgin female receptivity. Silencing adult Abd-B neu-rons significantly decreased receptivity. We characterize twocomponents of receptivity that are elicited in sexually maturefemalesby male courtship: pausing and vaginal plate opening.Silencing Abd-B neuronsdecreased pausingbutdid not affectvaginal plate opening, demonstrating that these two compo-nentsoffemalesexualbehaviorarefunctionallyseparable.Syn-theticactivationofAbd-Bneuronsincreasedpausing,butmalecourtship song alone was not sufficient to elicit this behavior.Conclusions: Our results provide an entry point to the neuralcircuit controlling virgin female receptivity. The female inte-gratesmultiplesensorycuesfromthemaletoexecutediscretemotor programs prior to copulation. Abd-B neurons controlpausing,akeyaspectoffemalesexualreceptivity,inresponseto male courtship.IntroductionTo choose their mates, male and female vinegar flies(Drosophila melanogaster) perform a duet of sexually dimor-phic courtship behaviors that offers an excellent model forstudying the neural circuitry of innate social behavior [1].Malecourtshipiscomposedofaseriesofdiscreteandstereo-typed motor programs such as following the female, produc-ing courtship song using a single extended wing, tappingand licking her genitals, and finally, copulating [1]. The neuralcircuitry underlying several of these behavioral componentshas been identified and dissected [2]. In contrast, very littleis known about how the female evaluates male courtship todecide whether to mate and how she executes that decision.A female fly that engages in copulation is consideredreceptivetomalecourtship.Receptivitycomprisestherelativeabsenceofobviousrejectionbehaviors,slowingdowntoallowthe male to initiate copulation, and opening cuticular vaginalplates to allow access to the genitalia [3]. However, priorwork on receptivity measured only mating rate, a metric thatprovides little insight into the discrete motor programs thatfemales display in the context of courtship. Although classicalgenetic studies identified a region of the female brain [4] andgenes required for receptivity [5–10], neurons with a clearlydefined function specific to female behavior in courtship andmating have yet to be described.Much of the effort to understand female receptivity hasfocused on its regulation. Female sexual maturity developsoverthefirstfewdaysaftereclosion[11],andsexuallyimmatureadult females reject male courtship by running or jumpingaway and kicking and fluttering their wings [12]. After mating,femaleDrosophilatemporarilyswitchintoanunreceptivestatein which they extrude the ovipositor to reject male courtship[12]. They also increase egg laying. This postmating responseistriggeredbySexPeptide,whichactivatestheSexPeptideRe-ceptor (SPR)[13] in a subset of female reproductive tract sen-sory neurons labeled by pickpocket (ppk), fruitless (fru), anddoublesex (dsx)[14–16]. Although recent work has continuedtoidentifyneuronsthatfunctiontocoordinatelyregulaterecep-tivity and egg-laying [14, 17], neurons with specific functionsrestricted to virgin mating behavior are still unknown.Males present an array of sensory cues during courtship,including contact and volatile pheromones and courtshipsong. It is not known which sensory signals trigger individualcomponents of receptivity and whether these componentsare coordinately or independently controlled by female neu-ral circuitry. Song seems critical to the courtship processbecause males muted by having their wings removed havedramaticallyreducedmatingsuccess[18].However,itremainsunclear to what degree females integrate sensory input fromcourtship song with other male courtship cues and how songaffects their behavior [19–21].Toexpandthemechanistic understandingofDrosophilavir-gin female receptivity, we set out to characterize its compo-nent motor programs and identify neurons directly involvedin this behavior. Using a genome-wide neuronal RNAi screen,we discovered a requirement for the homeobox (Hox) tran-scription factor Abdominal-B (Abd-B) in developing neuronsfor female receptivity. Adult Abd-B-Gal4 neurons located inthe abdominal ganglion and reproductive tract project locallywithin these areas and to higher brain centers. These neuronsare functionally required for female receptivity and act toinduce pausing in response to multiple male courtship cues.In addition to demonstrating a role for Abd-B in sex-specificbehavior, our results identify a neuronal subset responsiblefor a discrete component of virgin female receptivity.ResultsAn RNAi Screen Identifies Genes Required in Neurons forFemale Reproductive BehaviorsWe reasoned that genes and neural circuitry required forvirgin female receptivity could be identified within hits of a