List of Drosophila stocks used in this study.

The distinct textural properties of fruits in varying stages of ripening present unique ecological opportunities for several species of fruit flies, resulting, over evolutionary times, in specialized egg-laying behaviors. In this study we identified a TrpA channel-dependent mechanosensory pathway in the legs, through the gene painless, that modulates the discernment of softer patches for oviposition in gravid D. melanogaster females. We report that the stiffness-sensing role of tarsi is mediated through external sensory organs, namely ventral mechanosensory bristles and subsets of campaniform sensilla present primarily at the joints between tarsomeres. Our findings provide new evidence that campaniform sensilla function as indirect stiffness sensors of oviposition substrates, owing to their placement at joints that experience maximal cuticular distortion. We show that Painless is expressed in mechanosensory neurons innervating peripheral organs and is necessary for their functions in mediating oviposition substrate selection in gravid females. Furthermore, we observed that overexpression of painless in both campaniform sensilla and mechanosensory bristles partially rescues preference for the softer substrates in painless mutants, indicating that painless activity in these organs is necessary to mediate the preference. We propose that different interactions with a soft vs. a hard substrate (compression of the cuticle, distribution of contacts) results in differential mechanotransduction in painless-expressing neurons, determining oviposition preferences.处于不同成熟阶段的果实所具备的独特质地特性，为多种果蝇物种提供了独特的生态机遇，进而在进化历程中催生出特化的产卵行为。本研究中，我们在果蝇腿部通过无痛基因（painless）鉴定出一条依赖于TRPA通道（TrpA channel）的机械感觉通路，该通路可调控怀卵黑腹果蝇（D. melanogaster）雌体对柔软产卵位点的识别能力。我们发现，跗节（tarsi）的硬度感知功能是通过外部感觉器官介导的，具体为主要分布于跗分节关节处的腹侧机械感觉刚毛以及部分钟形感器（campaniform sensilla）。本研究结果为钟形感器作为产卵底物的间接硬度感受器提供了新的实验依据，这是由于该感器定位于表皮变形程度最大的关节处。我们证实，无痛基因（Painless）在支配外周感觉器官的机械感觉神经元中表达，且对于怀卵雌果蝇介导产卵底物选择的相关功能不可或缺。此外，我们观察到，在钟形感器和机械感觉刚毛中同时过表达无痛基因（painless），可部分挽救无痛基因突变体对柔软底物的产卵偏好，这表明上述两类器官中的无痛基因活性对于介导该偏好行为至关重要。我们提出，果蝇与柔软底物和坚硬底物的不同相互作用（即表皮压缩、接触点分布差异）会在表达无痛基因的神经元中引发差异化的机械转导过程，进而决定其产卵偏好。