Establishment of the circuit of the mushroom body calyx during development

感官信息的正确评估，准确行为目标的定义，运动的协调控制，都依赖于神经系统中精心设计的信息流——由神经元网络的结构保证。在发育过程中，神经元迁移到确定的目标位置，并分化出复杂的、神经元类型特异性的轴突和树突。在到达适当的目标区域后，它们面临的主要任务是在众多伙伴中识别正确的伙伴，并产生适当数量的连接。随着基于电子显微镜的神经元电路重建提供的分辨率水平，局部微电路结构的复杂性最近变得更加清晰。在蘑菇体（MB）花萼内，感觉信息被处理以引起Kenyon细胞（KCs）的稀疏响应代码。我们正在进行的由FOR2705资助的工作表明，MB（以及许多进化过程中的电路）的这种基本特性依赖于MB花萼的主要结构单元微肾小球（mg）的结构。我们专注于嗅觉信息的处理，并描述了在每个MG中，嗅觉投射神经元的轴突钮扣是如何被许多KCs的树突包围的，从而形成了一个由高度互联元素组成的球形结构。根据我们的描述水平，mg似乎是解决开发过程中如何形成特定连接的理想系统。然而，对于mg是如何产生的，我们几乎一无所知。我们建议在这里揭示关键的分子因素和基本逻辑，这些复合体如何进行经典的遗传筛选组装。利用转录组学数据，我们定义了一组由投射神经元或KCs表达的表面分子，作为支持花萼中神经元-神经元识别的候选分子。我们将通过RNAi介导的敲除来筛选mg、投射神经元钮扣、KC树突或它们的突触接触没有正确形成、维持或定位的情况。最好的候选分子将通过遗传学、高分辨率成像和细胞生物学技术的结合进行彻底的分析。为了支持这些研究并帮助阐明突变表型是如何出现的，我们将使用延时成像技术研究发育过程中单个轴突和树突的动态行为，并解决这一过程中活动的影响。最后，除了由mg代表的局部微电路外，我们还将通过生成感官表征图来解决MB花萼的全球组织逻辑。我们将讨论这幅地图是如何出现的，以及它在个人之间的刻板印象。综上所述，我们将在完整电路的功能特性的背景下，为成年果蝇大脑中关键电路的发育组装逻辑奠定基础。

The correct evaluation of sensory information, the definition of an accurate behavioral goal, the coordinated control of movement, all depend upon carefully designed flows of information within the nervous system – guaranteed by the architecture of neuronal networks. During development, neurons migrate to defined target locations and differentiate their complex and neuron-type specific axon and dendrites. Having reached their appropriate target region, they face the major tasks of identifying their correct partners among many and of generating connections in appropriate numbers. With the level of resolution provided by electron microscopy-based reconstructions of neuronal circuits, the complexity of local microcircuit architecture has recently emerged even more clearly. Within the mushroom body (MB) calyx, sensory information is processed to elicit a sparse code of response by the Kenyon cells (KCs). Our ongoing work, funded by the FOR2705, indicates that this fundamental property of the MB (and of many circuits across evolution) relies on the architecture of the main structural unit of the MB calyx, the microglomeruli (MGs). We concentrate on the processing of olfactory information and have described how, within each MG, the axonal bouton of an olfactory projection neuron is surrounded by the dendrites of many KCs to form a spherical structure of highly interconnected elements. With the level of description we produced, MGs seem an ideal system to address how specific connections are formed during development. However, virtually nothing is known about how MGs arise. We propose here to reveal key molecular factors and the fundamental logic of how these complexes assemble by performing a classic genetic screen. Using transcriptomic data, we have defined a set of surface molecules expressed by projection neurons or by KCs as candidates for supporting neuron-neuron recognition in the calyx. We will screen by RNAi- mediated knock-down for conditions in which the MGs, the projection neuron boutons, the KC dendrites or their synaptic contacts are not correctly formed, maintained or positioned. The best molecular candidates will be thoroughly analyzed with a combination of genetics, high-resolution imaging and cell biology techniques. To support these studies and help clarifying how mutant phenotypes emerged, we will investigate with time-lapse imaging the dynamic behavior of individual axons and dendrites during development and address the impact of activity during the process. Finally, in addition to the local microcircuits represented by the MGs, we will address also the logic of the global organization of the MB calyx, by generating a map of sensory representation. We will address how this map emerges and its stereotypy among individuals. Taken together, we will lay the ground of the logic of developmental assembly of a key circuit in the adult fly brain – in the context of the functional properties of the completed circuit.