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

这个Emmy Noether项目的重点是了解模式生物果蝇在轴-树突突触连接的蘑菇体（mb）内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成果，我们能够确定一种涉及尼古丁乙酰胆碱受体的突触后记忆存储的新机制（Pribbenow等人，手稿附）。虽然我们已经对记忆存储机制有了很好的理解，但新信息和所学信息是如何瞬间整合的，在很大程度上仍然不清楚。这个项目现在建立在发现轴-轴突突触基序的基础上，我们发现了记忆存储位点下游的一个突触（未发表）。这种连接的功能依赖于α - 7烟碱受体的信号传导，该受体也在脊椎动物的突触前信号传导中被发现。重要的是，α - 7烟碱受体的敲除干扰了行为程序，并改变了沿同一轴突分支的单个钮扣的神经生理特性。分子上，我们的数据表明alpha7亚基可以直接与突触囊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形成与规范途径平行的神经递质释放。由于我们在Emmy Noether项目中发现了信号睡眠压力网络中的类似基序（Raccuglia et al., 2019），因此我们假设轴突-轴突连接中的alpha7信号代表了网络整合的一般基序。在这里，我们将利用携带gfp标记的内源性alpha7的果蝇来研究轴-轴突接触的分子结构。同时，我们将分别研究MB输出神经元和R5环神经元在嗅觉和视觉整合背景下轴-轴突信号传导的神经生理原理，并利用光学传感器探讨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，它可能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on the discovery of an axo-axonal synaptic motif that we uncovered one synapse downstream of memory storage sites (unpublished).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.