Among the sensory modalities involved in controlling mating behavior in Drosophila melanogaster, contact sex pheromones play a primary role. The key receptor neurons for contact sex pheromones are located on the forelegs, which are activated in males upon touching the female abdomen during tapping events in courtship actions. A fruitless (fru)-positive (fru [+]) male-pheromone sensing cell (M-cell) and a fru [+] female-pheromone sensing cell (F-cell) are paired in a sensory bristle on the legs, and some fru [+] chemoreceptor axons project across the midline in the thoracic neuromere in males but not in females. However, the receptor cells that form sexually dimorphic axon terminals in the thoracic ganglia remain unknown. By generating labeled single-cell clones, we show that only a specific subset of fru [+] chemosensory neurons have axons that cross the midline in males. We further demonstrate that there exist two male-specific bristles, each harboring two chemosensory neurons; neither of which exhibits midline crossing, a masculine characteristic. This study reveals hitherto unrecognized sex differences in chemosensory neurons, imposing us to reinvestigate the pheromone input pathways that impinge on the central courtship circuit.

在控制果蝇的交配行为的感觉方式中，接触性信息素起主要作用。接触性信息素的关键受体神经元位于前肢上，在求爱动作中的敲击事件中，一旦接触雌性腹部，雄性就会激活。甲徒劳（FRU）阳性（FRU [+]）雄性信息素感应单元（M-细胞）和FRU [+]阴信息素感应单元（F-小区）被配对在上腿感官刷毛，和一些FRU[+]化学感受器轴突在男性的胸神经绒毛中线突出，但在女性中没有。但是，在胸神经节中形成有性双态轴突末端的受体细胞仍然是未知的。通过生成标记的单细胞克隆，我们显示只有fru [+]化学感应神经元的特定子集具有跨越男性中线的轴突。我们进一步证明存在两个雄性特有的鬃毛，每个鬃毛都带有两个化学感觉神经元。两者都没有表现出中线交叉，这是男性特征。这项研究揭示了化学感应神经元迄今未认识到的性别差异，迫使我们重新研究影响中央求爱回路的信息素输入途径。