Genetic access to synaptic mechanisms of memory in the behaving animal - Axo-axonal synaptic integration in control of neurotransmitter release

这个艾美奖Noether项目的重点是了解模式生物果蝇蘑菇体(MBS)在轴-树突触交界处的食欲记忆存储的突触机制(Owald等人，2015；Perisse，Owald等人，2016；Barnstedt，Owald等人，2016)。作为这个项目的一个关键结果，我们能够识别出一种涉及烟碱型乙酰胆碱受体的突触后记忆存储的新机制(Pribbenow等人，手稿附后)。虽然我们已经对记忆存储机制有了很好的理解，但新的和学习到的信息是如何瞬间整合在一起的，在很大程度上仍然不清楚。这里提出的项目现在建立在一个轴突-轴突突触主题的发现上，我们发现了记忆存储位置下游的一个突触(未发表)。这种连接的功能依赖于通过α7尼古丁受体的信号，该受体在脊椎动物的突触前信号中也被发现。重要的是，α7烟碱受体基因敲除干扰了行为程序，改变了沿着同一轴突分支的单个突起的神经生理学特性。在分子方面，我们的数据表明，Alpha7亚基可以直接与突触小泡释放机制的蛋白质相互作用。因此，我们假设，Alpha7可以通过电压门控钙通道平行于规范途径来塑造神经递质的释放。因为我们在这个艾美奖Noether项目(Raccuglia等人，2019年)中发现了一个类似的网络中发出睡眠压力信号的基序，所以我们遵循这样的假设，即轴突连接中的Alpha7信号传递代表着网络整合的一个一般基序。在这里，我们将利用我们在这个项目中构建的携带GFP标记的内源性Alpha7的苍蝇来研究轴突接触的分子结构。同时，我们将分别在嗅觉和视觉整合MB输出神经元和R5环神经元的背景下，研究轴突信号的神经生理学原理，询问使用光学传感器的神经递质释放的后续步骤。总之，该项目旨在从结构(分子)和功能上研究一种新的突触基序，该基序可能能够参与信息整合和即时决策。

This Emmy Noether project focuses on understanding the synaptic mechanisms of appetitive memory storage within the mushroom bodies (MBs) of the model organism Drosophila at an axo-dendritic synaptic junction (Owald et al., 2015; Perisse, Owald et al., 2016; Barnstedt, Owald et al., 2016). As a key result of this project, we were able to identify a novel mechanism of postsynaptic memory storage involving nicotinic acetylcholine receptors (Pribbenow et al., manuscript attached). While we have come to a good understanding of memory-storage mechanisms, how novel and learnt information are instantaneously integrated remains largely unclear. The here proposed project now builds on the discovery of an axo-axonal synaptic motif that we uncovered one synapse downstream of memory storage sites (unpublished). Functionality of this connection relies on signaling through the alpha7 nicotinic receptor that has also been identified in presynaptic signaling in vertebrates. Importantly, alpha7 nicotinic receptor knock-down interfered with behavioral programs and altered neurophysiological properties of individual boutons along the same axonal branch. Molecularly, our data suggest that alpha7 subunits can directly interact with proteins of the synaptic vesicle release machinery. We thus hypothesize that alpha7 can shape neurotransmitter release in parallel to canonical pathways via voltage-gated calcium channels. Because we uncovered a similar motif within a network signaling sleep pressure in this Emmy Noether project (Raccuglia et al., 2019), we follow the hypothesis that alpha7-signalling at axo-axonal connections represents a general motif for network integration.Here, we will investigate the molecular structure of axo-axonal contacts utilizing flies harboring GFP-tagged endogenous alpha7 that we constructed in this project. In parallel, we will investigate neurophysiological principles of axo-axonal signaling in the context of olfactory and visual integration of MB output neurons and R5 ring neurons respectively, interrogating subsequent steps of neurotransmitter release using optical sensors. Together, this project aims at structurally (molecularly) and functionally investigating a novel synaptic motif potentially capable of partaking in information integration and instant decision making.