果蝇嗅觉神经元的信号转导

The first step in olfaction is olfactory transduction, the conversion of odor information into neuronal electrical signals by olfactory sensory neurons (OSNs). Over the past decade, extensive investigations have led to a major controversy in understanding olfactory transduction by Drosophila OSNs. On one hand, ample evidence has demonstrated a metabotropic olfactory transduction that is mediated by G-protein signaling in Drosophila; on the other hand, however, strong evidence also supports an ionotropic olfactory transduction that is independent of G-protein signaling. In any case, most of the prior studies of olfactory transduction in Drosophila were carried out in culture cells such as HEK 293 cells. The cellular signaling environment differs dramatically between Drosophila OSNs and the culture cells. Thus, the understanding gained from the culture-cell studies may not be able to apply directly to Drosophila OSNs. Recently, we have developed the first patch-clamp recordings from native Drosophila OSNs, overcoming the decades-long obstacle in the field. Here, we propose to apply our novel patch-clamp recording technique, together with neural pharmacology and molecular genetics, to address this burning question of olfactory transduction in Drosophila OSNs. Aim 1: we will systematically measure the precise response kinetics from many OSNs that express very different odorant receptors (Ors), which shall provide important clues to understand the signaling cascades mediated odorant responses. Aim 2: we will combine electrophysiology with neural pharmacology to examine contributions of known signaling molecules, such as G-proteins, adenylyl cyclase and cyclic-nucleotide-gated channels, to odorant responses in Drosophila OSNs. Aim 3: we will use fly genetics to manipulate individual signaling genes to dissect its role in Drosophila olfactory transduction. The proposed investigation will enhance our understanding of olfaction in both Drosophila and mammals because they share many similar and conserved olfactory mechanisms. In addition, many disease-propagating insects and crop-consuming insects rely on olfaction for finding host or for reproduction. Thus, the knowledge gained from the proposed research will facilitate insect control, improve human health and agricultural economy.

嗅觉感知起始于嗅觉神经元对气味刺激的信号转导。果蝇嗅觉信号转导在过去几十年来一直是领域内争论的焦点。由于在体果蝇电生理记录的困难，以往的研究集中于体外表达系统。一些实验表明，果蝇的嗅觉转导依赖G蛋白信号通路；另一些则表明，气味刺激直接打开离子通道。但培养细胞和果蝇嗅觉神经元在胞内信号分子与环境方面大为不同，因此培养细胞上的结果不能直接简单应用于果蝇嗅觉神经元。在此，我们利用本实验室新发展的果蝇嗅觉神经元膜片钳记录，研究：1）嗅觉神经元对气味反应慢动力学的普适性；2）结合神经药理学，研究G蛋白通路是否参与嗅觉神经元信号转导；3）结合果蝇遗传学敲除各种信号蛋白，检测其在果蝇嗅觉信号转导中的作用。本研究可加深我们对果蝇嗅觉信号转导机制的认识，也可为哺乳动物中尚未解决的嗅觉转导提供思路。同时，我们的研究还具有社会和经济价值，可为更好地控制有害昆虫，促进人类健康，增加农作物产量等提供理论指导。

果蝇嗅觉信号转导在过去几十年来一直是领域内争论的焦点。本实验室利用首创的果蝇 OSNs 膜片钳记录技术，结合神经药理学和分子遗传学等方法系统解析了嗅觉转导的分子机制，我们发现：1）Or22a-OSNs利用Gs-cAMP信号通路进行嗅觉转导，而其它Or-OSNs不依赖于G蛋白，为离子通道所直接门控；2）利用异位表达Or的方式，发现果蝇嗅觉转导既依赖于Or类型，也依赖于细胞环境；3）Or共受体(ORCO)在信号转导中也有重要作用；4）连接 Or22a 相邻跨膜结构的第2、4、6个环可能与G蛋白激活相关。所以，Or47a与大多数其他Or为离子型嗅觉受体，而Or22a既是G蛋白偶联受体，同时又是信号转导离子通道的组成部分，从而可兼顾信号转导的灵敏度和速度。