Cellular dissection of the neural circuits processing and integrating skylight cues in the brain of the fruit fly Drosophila melanogaster

视觉系统必须提取、处理和整合关于不同视觉线索的信息，以便向行为输出提供信息。对昆虫大脑处理和整合特定天体信号(如天光偏振、颜色梯度和地标)的神经电路的解剖为理解从细胞/突触到生理/行为水平的处理和整合提供了一个独特的机会。该提案的目的是以果蝇为模型，与其他感觉系统进行比较，对潜在的回路机制提供全面的功能表征。许多昆虫使用天体信号来改善远距离导航，以及更多的局部定位任务。在“指南针路径”中，不同的天光信号，如天体的偏振、颜色和强度梯度，或天体的位置，都被处理过，并通过平行的路径传送到中央大脑。电生理记录显示，在视叶细胞类型中，偏振和染色信号的整合已经开始，在中央大脑中的一个视球--前视结节(AOTU)--变得越来越突出，AOTU是中央复合体的中继器。重要的是，果蝇在开阔的天空下以及在实验室条件下定向时也会使用偏振光。像许多其他昆虫一样，它们在成虫眼睛的一个特殊的“背缘区域”拥有对偏振敏感的光感受器，表现出对偏振敏感的生理反应。在为这项提议做准备时，我们已经积累了支持实验目标的初步数据：使用分子遗传学工具，我们现在能够解决有关处理天窗偏振的神经电路的功能连通性的重要公开问题，以及那些将偏振与其他视觉线索相结合的电路元件：(1)特定类型的细胞的活动将使用遗传编码指示器可视化，它们对行为动物的作用将在失活后进行测试。(2)横跨整个苍蝇脑(‘连接体’)的电子显微镜数据将揭示不同类型细胞之间突触连接的数量和分布；(3)功能性突触连接将通过系统地沉默或激活细胞类型来验证，同时成像中央大脑中下游元件的活动；(4)特定神经递质及其受体的机制将通过基因突变和细胞类型特异性救援来阐明。尽管对天光偏振、彩色信息或小物体的处理进行了研究，但COMPASS通路中确切的功能连接和整合仍然未知。我们将结合解剖学、生理学和行为学实验，通过解剖连接眼睛和AOTU的神经回路来弥合这一知识差距。

The visual system must extract, process, and integrate information about different visual cues in order to inform a behavioral output. The dissection of neural circuits in the insect brain processing and integrating specific celestial cues like skylight polarization, colour gradients, and landmarks offers a unique opportunity to understand how processing and integration is achieved, from a cellular/synaptic to a physiological/behavioural level. The goal of this proposal is to provide a comprehensive functional characterization of the underlying circuit mechanisms in comparison with other sensory systems using Drosophila melanogaster as a model. Many insects use celestial cues to improve navigation over long distances, as well as more local orientation tasks. In the ‘compass pathway’, different skylight cues such as celestial polarization, colour and intensity gradients, or the position of a celestial body, are processed and conveyed via parallel pathways to the central brain. Electrophysiological recordings showed that integration of polarization and chromatic cues already begins in optic lobe cell types, becoming increasingly prominent in the ‘anterior optic tubercle’ (AOTU), an optic glomerulus in the central brain that serves a relay to the central complex. Importantly, fruit flies also use polarized light when orienting under the open sky, as well as under laboratory conditions. Like many other insects they harbor polarization-sensitive photoreceptors in a specialized ‘dorsal rim area’ of the adult eye, which manifest polarization-sensitive physiological responses. In preparation for this proposal we have accumulated preliminary data that motivate the experimental aims: Using molecular genetic tools we are now in the position to address important open questions about the functional connectivity of the neural circuits processing skylight polarization, as well as those circuit elements integrating polarization with other visual cues: (1) The activity of specific cell types will be visualized using genetically encoded indicators and their role for the behaving animal will be tested after inactivation. (2) Electron microscopic data spanning the entire fly brain (the ‘connectome’), will reveal both number and distribution of synaptic connections between cell types; (3) Functional synaptic connections will be validated by systematically silencing or activating cell types, while imaging the activity of downstream elements in the central brain; (4) The mechanistic role of specific neurotransmitters and their receptors will be elucidated using genetic mutants and cell type specific rescue. Despite studies on processing of skylight polarization, chromatic information, or small objects, the exact functional connectivity and integration within the compass pathway remain unknown. We will close this gap in knowledge, by dissecting the neural circuits connecting the eye to the AOTU, using a combination of anatomy, physiology, and behavior experiments.