Erickson Timothy, Pacentine Itallia V, Venuto Alexandra, Clemens Rachel, Nicolson Teresa
Department of Biology, East Carolina University, Greenville, NC, United States.
Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, OR, United States.
Front Mol Neurosci. 2020 Jan 15;12:320. doi: 10.3389/fnmol.2019.00320. eCollection 2019.
Hair cells sense and transmit auditory, vestibular, and hydrodynamic information by converting mechanical stimuli into electrical signals. This process of mechano-electrical transduction (MET) requires a mechanically gated channel localized in the apical stereocilia of hair cells. In mice, lipoma HMGIC fusion partner-like 5 (LHFPL5) acts as an auxiliary subunit of the MET channel whose primary role is to correctly localize PCDH15 and TMC1 to the mechanotransduction complex. Zebrafish have two genes ( and ), but their individual contributions to MET channel assembly and function have not been analyzed. Here we show that the zebrafish genes are expressed in discrete populations of hair cells: expression is restricted to auditory and vestibular hair cells in the inner ear, while expression is specific to hair cells of the lateral line organ. Consequently, mutants exhibit defects in auditory and vestibular function, while disruption of affects hair cells only in the lateral line neuromasts. In contrast to previous reports in mice, localization of Tmc1 does not depend upon Lhfpl5 function in either the inner ear or lateral line organ. In both and mutants, GFP-tagged Tmc1 and Tmc2b proteins still localize to the stereocilia of hair cells. Using a stably integrated GFP-Lhfpl5a transgene, we show that the tip link cadherins Pcdh15a and Cdh23, along with the Myo7aa motor protein, are required for correct Lhfpl5a localization at the tips of stereocilia. Our work corroborates the evolutionarily conserved co-dependence between Lhfpl5 and Pcdh15, but also reveals novel requirements for Cdh23 and Myo7aa to correctly localize Lhfpl5a. In addition, our data suggest that targeting of Tmc1 and Tmc2b proteins to stereocilia in zebrafish hair cells occurs independently of Lhfpl5 proteins.
毛细胞通过将机械刺激转化为电信号来感知和传递听觉、前庭及流体动力学信息。这种机械电转导（MET）过程需要一个位于毛细胞顶端静纤毛中的机械门控通道。在小鼠中，脂肪瘤HMGIC融合伴侣样5（LHFPL5）作为MET通道的辅助亚基，其主要作用是将PCDH15和TMC1正确定位到机械转导复合体。斑马鱼有两个基因（ 和 ），但它们对MET通道组装和功能的各自贡献尚未得到分析。在这里，我们表明斑马鱼的 基因在不同的毛细胞群体中表达： 表达仅限于内耳的听觉和前庭毛细胞，而 表达则特异性地存在于侧线器官的毛细胞中。因此， 突变体在听觉和前庭功能上表现出缺陷，而 基因的破坏仅影响侧线神经丘中的毛细胞。与之前在小鼠中的报道相反，在内耳或侧线器官中，Tmc1的定位并不依赖于Lhfpl5的功能。在 和 突变体中，绿色荧光蛋白标记的Tmc1和Tmc2b蛋白仍能定位到毛细胞的静纤毛上。使用稳定整合的绿色荧光蛋白-Lhfpl5a转基因，我们表明，末梢连接钙黏蛋白Pcdh15a和Cdh23以及肌球蛋白7aa运动蛋白是Lhfpl5a在静纤毛顶端正确定位所必需的。我们的工作证实了Lhfpl5和Pcdh15之间进化上保守的相互依赖关系，但也揭示了Cdh23和Myo7aa对Lhfpl5a正确定位的新要求。此外我们的数据表明，在斑马鱼毛细胞中，Tmc1和Tmc2b蛋白定位到静纤毛的过程独立于Lhfpl5蛋白。
