Lelli Andrea, Asai Yukako, Forge Andrew, Holt Jeffrey R, Géléoc Gwenaëlle S G
Department of Neuroscience, University of Virginia School of Medicine, Charlottesville, Virginia 22908-1392, USA.
J Neurophysiol. 2009 Jun;101(6):2961-73. doi: 10.1152/jn.00136.2009. Epub 2009 Apr 1.
Inner ear hair cells are exquisite mechanosensors that transduce nanometer scale deflections of their sensory hair bundles into electrical signals. Several essential elements must be precisely assembled during development to confer the unique structure and function of the mechanotransduction apparatus. Here we investigated the functional development of the transduction complex in outer hair cells along the length of mouse cochlea acutely excised between embryonic day 17 (E17) and postnatal day 8 (P8). We charted development of the stereociliary bundle using scanning electron microscopy; FM1-43 uptake, which permeates hair cell transduction channels, mechanotransduction currents evoked by rapid hair bundle deflections, and mRNA expression of possible components of the transduction complex. We demonstrated that uptake of FM1-43 first occurred in the basal portion of the cochlea at P0 and progressed toward the apex over the subsequent week. Electrophysiological recordings obtained from 234 outer hair cells between E17 and P8 from four cochlear regions revealed a correlation between the pattern of FM1-43 uptake and the acquisition of mechanotransduction. We found a spatiotemporal gradient in the properties of transduction including onset, amplitude, operating range, time course, and extent of adaptation. We used quantitative RT-PCR to examine relative mRNA expression of several hair cell myosins and candidate tip-link molecules. We found spatiotemporal expression patterns for mRNA that encodes cadherin 23, protocadherin 15, myosins 3a, 7a, 15a, and PMCA2 that preceded the acquisition of transduction. The spatiotemporal expression patterns of myosin 1c and PMCA2 mRNA were correlated with developmental changes in several properties of mechanotransduction.
内耳毛细胞是精密的机械传感器，可将其感觉毛束的纳米级偏转转化为电信号。在发育过程中，几个关键要素必须精确组装，以赋予机械转导装置独特的结构和功能。在这里，我们研究了在胚胎第17天（E17）至出生后第8天（P8）之间急性切除的小鼠耳蜗长度上，外毛细胞中转导复合体的功能发育。我们使用扫描电子显微镜描绘了静纤毛束的发育过程；FM1-43摄取，它可透过毛细胞转导通道，快速毛束偏转诱发的机械转导电流，以及转导复合体可能成分的mRNA表达。我们证明，FM1-43的摄取首先在出生后第0天出现在耳蜗基部，并在随后一周向顶端发展。从四个耳蜗区域的234个外毛细胞在E17至P8之间获得的电生理记录显示，FM1-43摄取模式与机械转导的获得之间存在相关性。我们发现转导特性存在时空梯度，包括起始、幅度、工作范围、时间进程和适应程度。我们使用定量RT-PCR来检测几种毛细胞肌球蛋白和候选顶连接分子的相对mRNA表达。我们发现编码钙黏蛋白23、原钙黏蛋白15、肌球蛋白3a、7a、15a和质膜钙ATP酶2（PMCA2）的mRNA的时空表达模式先于转导的获得。肌球蛋白1c和PMCA2 mRNA的时空表达模式与机械转导的几个特性的发育变化相关。
