Institute of Developmental Biology and Neurobiology, Johannes Gutenberg University Mainz, Mainz, Germany.
J Neurogenet. 2020 Mar;34(1):133-150. doi: 10.1080/01677063.2020.1715972. Epub 2020 Jan 30.
Neuronal excitability is determined by the combination of different ion channels and their sub-neuronal localization. This study utilizes protein trap fly strains with endogenously tagged channels to analyze the spatial expression patterns of the four Shaker-related voltage-gated potassium channels, K1-4, in the larval, pupal, and adult ventral nerve cord. We find that all four channels (Shaker, K1; Shab, K2; Shaw, K3; and Shal, K4) each show different spatial expression patterns in the ventral nerve cord and are predominantly targeted to different sub-neuronal compartments. Shaker is abundantly expressed in axons, Shab also localizes to axons but mostly in commissures, Shaw expression is restricted to distinct parts of neuropils, and Shal is found somatodendritically, but also in axons of identified motoneurons. During early pupal life expression of all four Shaker-related channels is markedly decreased with an almost complete shutdown of expression at early pupal stage 5 (∼30% through metamorphosis). Re-expression of K1-4 channels at pupal stage 6 starts with abundant channel localization in neuronal somata, followed by channel targeting to the respective sub-neuronal compartments until late pupal life. The developmental time course of tagged K1-4 channel expression corresponds with previously published data on developmental changes in single neuron physiology, thus indicating that protein trap fly strains are a useful tool to analyze developmental regulation of potassium channel expression. Finally, we take advantage of the large diameter of the giant fiber (GF) interneuron to map channel expression onto the axon and axon terminals of an identified interneuron. Shaker, Shaw, and Shal but not Shab channels localize to the non-myelinated GF axonal membrane and axon terminals. This study constitutes a first step toward systematically analyzing sub-neuronal potassium channel localization in . Functional implications as well as similarities and differences to K1-4 channel localization in mammalian neurons are discussed.
神经元兴奋性是由不同离子通道及其亚神经元定位的组合决定的。本研究利用内源标记通道的蛋白陷阱果蝇品系，分析了四个 Shaker 相关电压门控钾通道（K1-4）在幼虫、蛹和成年 腹神经索中的空间表达模式。我们发现，所有四个通道（Shaker、K1；Shab、K2；Shaw、K3；和 Shal、K4）在 腹神经索中均表现出不同的空间表达模式，并且主要靶向不同的亚神经元隔室。Shaker 在轴突中大量表达，Shab 也定位于轴突，但主要在神经节中，Shaw 的表达仅限于神经节的特定部分，Shal 则在体树突中表达，但也存在于已鉴定的运动神经元的轴突中。在早期蛹期，所有四个 Shaker 相关通道的表达明显降低，在早期蛹期 5 时（约 30%通过变态）表达几乎完全关闭。K1-4 通道在蛹期 6 的重新表达始于神经元胞体中丰富的通道定位，随后通道靶向各自的亚神经元隔室，直到晚期蛹期。标记 K1-4 通道表达的发育时间过程与先前关于单个神经元生理学发育变化的发表数据相对应，因此表明蛋白陷阱果蝇品系是分析钾通道表达发育调控的有用工具。最后，我们利用巨大纤维（GF）中间神经元的大直径将通道表达映射到已鉴定的中间神经元的轴突和轴突末端。Shaker、Shaw 和 Shal 但不是 Shab 通道定位于未髓鞘化的 GF 轴突膜和轴突末端。本研究是系统分析 钾通道亚神经元定位的第一步。讨论了功能意义以及与哺乳动物神经元中 K1-4 通道定位的相似性和差异性。
