The role of NompC (=TRPN1) for mechanotransducer gating and adaptation in the Drosophila ear

所有感觉的核心都有一个共同的过程：感觉细胞膜上专用离子通道的打开或关闭（称为门控）。这些所谓的感觉换能器通道将外部刺激能量——比如声波中包含的机械能——转换成流经感觉细胞膜的电流。在经典机械感官的情况下，即触觉、听觉和平衡感，这些机械换能器通道被认为是通过最直接的方式进行门控的，即通过刺激力本身。这种直接激活模式意味着换能器必须以某种方式与专门的刺激接收器结构机械耦合，例如我们的耳鼓或果蝇的天线声音接收器。然而，具有讽刺意味的是，它们的激活模式惊人的简单，似乎使迄今为止真正的机械换能器通道的分子识别变得非常复杂。最近，研究表明，果蝇耳朵感觉细胞的机械转导依赖于机械转导通道，其运作原理与脊椎动物内耳的生物物理原理相同。幸运的是，在果蝇中，这些传感器通道的功能可以在完整果蝇的耳朵中进行体内评估。考虑到果蝇巨大的遗传易感性，以及大量机械感觉突变体的可用性，果蝇耳朵因此构成了一个理想的系统，用于探索已识别蛋白质在机械感觉过程中的特定作用，特别是它们对机械转导的贡献。这一提议将通过具体评估称为NompC的离子通道的作用，启动果蝇耳朵中机械传感器功能的分子解剖。据报道，NompC通道在脊椎动物和无脊椎动物的耳朵中都具有机械感觉功能，是目前真正的听觉机械传感器通道的最佳候选。果蝇和脊椎动物耳朵中的机械换能器的一个共同特征似乎是它们适应持续刺激的能力：在脊椎动物毛细胞中，这种适应是由专门的适应马达介导的，它的作用是释放那些将力耦合到换能器通道上的元素的张力，从而允许通道在刺激存在的情况下关闭。最值得注意的是，果蝇耳朵中传感器通道的适应性似乎与脊椎动物的运作方式相同。一些证据表明NompC参与果蝇的机械转导或机械转导适应过程，但更直接的证据仍未得到证实。通过使用生物物理、转基因和建模方法，我将研究NompC对果蝇耳朵的机械转导和/或适应的具体贡献。尽管在非哺乳动物的耳朵中存在NompC通道，但在哺乳动物的耳朵中似乎不存在，但本文提出的研究也将为更好地理解我们自己耳朵的工作原理提供帮助。对非哺乳动物脊椎动物的研究，如海龟和青蛙，提供了许多关于听觉功能的基本机制的见解，这些机制也适用于哺乳动物。这项对果蝇的研究同样有望对我们对耳朵如何将声音提供的机械力转化为电信号的分子理解做出重大贡献，这些电信号可以在大脑中进一步处理。

At the heart of all sensation lies a common process: The opening or closing (called the gating) of dedicated ion channels in the membranes of sensory cells. These so-called sensory transducer channels convert external stimulus energy- such as the mechanical energy contained in a sound wave- into an electrical current that flows through the sensory cell's membrane. In the case of the classical mechanical senses, i.e. the senses of touch, hearing and balance, these mechano-transducer channels are deemed to be gated in the most direct way possible, namely by the stimulus forces themselves. This direct mode of activation implies that the transducers must somehow be mechanically coupled to specialized stimulus receiver structures, such as our ear drums or the antennal sound receivers of fruit flies, for example. Somewhat ironically, however, the astonishing simplicity of their mode of activation appears to have greatly complicated the molecular identification of true mechano-transducer channels to this day. Recently, it was demonstrated that mechano-transduction in the sensory cells of the fruit-fly (Drosophila) ear, relies on mechano-transducer channels that operate according to the same biophysical principles as those in the inner ears of vertebrates. Fortunately, in Drosophila, the function of these transducer channels can be assessed in vivo, in the ears of intact flies. Given the enormous genetic tractability of the fruit fly, along with the availability of a multitude of mechano-sensory mutants, the Drosophila ear therefore constitutes an ideal system in which to probe the specific roles of identified proteins in the process of mechano-sensation, particularly their contributions to mechano-transduction. This proposal will initiate the molecular dissection of mechano-transducer function in the Drosophila ear by specifically assessing the role of an ion channel called NompC. The NompC channel, which reportedly serves mechanosensory functions in the ears of both vertebrates and invertebrates, is presently the best candidate for a true, auditory mechano-transducer channel. A common feature of mechano-transducers in the ears of both fruit flies and vertebrates seems to be their ability to adapt to a maintained stimulus: in vertebrate hair cells this adaptation is mediated by specialized adaptation motors which act to release tension from those elements that couple forces to the transducer channels, thus allowing for the channels to close despite the presence of the stimulus. Most remarkably, the adaptation of transducer channels in the Drosophila ear appears to operate in the same way as in vertebrates. Several lines of evidence have suggested an involvement of NompC in the process of mechano-transduction or mechano-transducer adaptation in Drosophila but more direct evidence remains outstanding. By using biophysical, transgenetic and modelling approaches, I will investigate the specific contribution of NompC to mechano-transduction and/or adaptation in the Drosophila ear. Despite the fact that the NompC channel, though present in the ears of non-mammalian vertebrates, seems to be absent from the ears of mammals, the study proposed here will also provide for a better understanding of our own ears' workings. Studies in non-mammalian vertebrates, such as turtles and frogs have provided much insight into fundamental mechanisms of auditory function that also apply in mammals, This study in the fruit fly is likewise expected to make a significant contribution to our molecular understanding of how ears translate the mechanical forces provided by sound into electrical signals which can be processed further on in the brain.