Multimodal and multisensory coding in the Drosophila larval peripheral gustatory center

The ability to evaluate food palatability is innate in all animals from insects to mammals, ensuring their survival. The external taste organ at the periphery in Drosophila larvae is composed of only few sensory neurons but displays discrimination between a wide range of chemicals as well as a high level of complexity in receptor expression and cell response profile. Taking advantage of this architecturally simple but functionally complex sensory system, we tackled dissection of taste coding at organ level with cellular resolution. We combined whole-organ calcium imaging and single-cell transcriptomics to map physiological properties and molecular features of individual sense neurons. In line with taste multimodality, about one third of gustatory sense neurons responded to multiple tastants. Reinforcing on the peripheral integration of signals, we observed neuronal deactivation events within simultaneous neighboring responses, submitting the probability of inter-cellular communication through electrical coupling. Furthermore, we identified neurons responding to both mechanical and taste stimulation, indicating potential multisensory integration. On a molecular level, chemosensory cells show heterogeneity in neuromodulator expression. In addition to a broad cholinergic profile, markers on dopaminergic, glutamatergic or neuropeptidergic pathways are present either in distinct cell populations or are seemingly co-expressed. Our data further extend the sensory capacity of the larval taste system showing a large degree of multimodal as well as multisensory coding principles. Overall design: Fluorescently labelled sense organs were manually isolated and further treated enzymatically for single cell dissociation. We then completed DisCo workflow and generated cDNA libraries.

从昆虫到哺乳动物的所有动物均天生具备评估食物适口性的能力，这是其生存的必要保障。果蝇幼虫（Drosophila larvae）外周的外部味觉器官仅由少量感觉神经元构成，却能够区分种类繁多的化学物质，且在受体表达与细胞响应特征上呈现高度复杂性。借助这一结构简洁却功能复杂的感觉系统，我们着手在细胞分辨率下解析器官层面的味觉编码机制。我们结合全器官钙成像（whole-organ calcium imaging）与单细胞转录组学（single-cell transcriptomics）技术，绘制了单个感觉神经元的生理特性与分子特征图谱。与味觉的多模态特性相符，约三分之一的味觉感觉神经元会对多种味觉刺激物产生响应。为进一步验证外周信号整合现象，我们观察到相邻神经元同时响应时会出现神经去激活事件，提示存在通过电耦合实现细胞间通信的可能性。此外，我们还鉴定出可同时响应机械刺激与味觉刺激的神经元，表明存在潜在的多感觉整合机制。在分子层面，化学感觉细胞在神经调质（neuromodulator）表达上呈现异质性。除了广泛存在的胆碱能（cholinergic）特征外，多巴胺能（dopaminergic）、谷氨酸能（glutamatergic）或神经肽能（neuropeptidergic）通路的标志物既可分布于不同的细胞群中，也似乎存在共表达现象。我们的数据进一步拓展了果蝇幼虫味觉系统的感知能力，揭示了其具备高度的多模态及多感觉编码原则。整体实验设计：我们手动分离了经荧光标记的感觉器官，随后通过酶解法完成单细胞解离。之后我们完成了DisCo流程并构建了cDNA文库。