Institute for Auditory Neuroscience, University Medical Center Göttingen, 37075 Göttingen, Germany.
InnerEarLab, University Medical Center Göttingen, 37075 Göttingen, Germany.
Proc Natl Acad Sci U S A. 2019 Apr 30;116(18):9084-9093. doi: 10.1073/pnas.1818358116. Epub 2019 Apr 11.
Encoding the wide range of audible sounds in the mammalian cochlea is collectively achieved by functionally diverse type I spiral ganglion neurons (SGNs) at each tonotopic position. The firing of each SGN is thought to be driven by an individual active zone (AZ) of a given inner hair cell (IHC). These AZs present distinct properties according to their position within the IHC, to some extent forming a gradient between the modiolar and the pillar IHC side. In this study, we investigated whether signaling involved in planar polarity at the apical surface can influence position-dependent AZ properties at the IHC base. Specifically, we tested the role of Gαi proteins and their binding partner LGN/Gpsm2 implicated in cytoskeleton polarization and hair cell (HC) orientation along the epithelial plane. Using high and superresolution immunofluorescence microscopy as well as patch-clamp combined with confocal Ca imaging we analyzed IHCs in which Gαi signaling was blocked by Cre-induced expression of the pertussis toxin catalytic subunit (PTXa). PTXa-expressing IHCs exhibited larger Ca1.3 Ca-channel clusters and consequently greater Ca influx at the whole-cell and single-synapse levels, which also showed a hyperpolarized shift of activation. Moreover, PTXa expression collapsed the modiolar-pillar gradients of ribbon size and maximal synaptic Ca influx. Finally, genetic deletion of and also disrupted the modiolar-pillar gradient of ribbon size. We propose a role for Gαi proteins and LGN in regulating the position-dependent AZ properties in IHCs and suggest that this signaling pathway contributes to setting up the diverse firing properties of SGNs.
哺乳动物耳蜗中广泛的可听声音的编码是通过每个音调位置的功能多样的 I 型螺旋神经节神经元 (SGN) 共同实现的。每个 SGN 的放电被认为是由特定内毛细胞 (IHC) 的单个活性区 (AZ) 驱动的。这些 AZ 根据它们在 IHC 中的位置具有不同的特性，在一定程度上在毛细胞的 modiolar 和 pillar 侧之间形成梯度。在这项研究中，我们研究了在顶表面涉及平面极性的信号是否会影响 IHC 基部位置依赖的 AZ 特性。具体来说，我们测试了 Gαi 蛋白及其结合伴侣 LGN/Gpsm2 的作用，这些蛋白参与细胞骨架极化和毛细胞 (HC) 沿着上皮平面的定向。使用高分辨率和超分辨率免疫荧光显微镜以及与共聚焦 Ca 成像结合的膜片钳技术，我们分析了 Gαi 信号通过 Cre 诱导表达百日咳毒素催化亚基 (PTXa) 阻断的 IHC。表达 PTXa 的 IHC 表现出更大的 Ca1.3 Ca 通道簇，因此在全细胞和单个突触水平的 Ca 内流更大，其激活也表现出超极化偏移。此外，PTXa 表达破坏了 ribbon 大小和最大突触 Ca 内流的 modiolar-pillar 梯度。最后， 和 的基因缺失也破坏了 ribbon 大小的 modiolar-pillar 梯度。我们提出 Gαi 蛋白和 LGN 在调节 IHC 中位置依赖的 AZ 特性中的作用，并表明该信号通路有助于建立 SGN 多样化的放电特性。
