Oregon Hearing Research Center and Vollum Institute, Oregon Health & Science University, Portland, Oregon, United States of America.
PLoS Genet. 2019 Feb 6;15(2):e1007635. doi: 10.1371/journal.pgen.1007635. eCollection 2019 Feb.
Mutations in transmembrane inner ear (TMIE) cause deafness in humans; previous studies suggest involvement in the mechano-electrical transduction (MET) complex in sensory hair cells, but TMIE's precise role is unclear. In tmie zebrafish mutants, we observed that GFP-tagged Tmc1 and Tmc2b, which are subunits of the MET channel, fail to target to the hair bundle. In contrast, overexpression of Tmie strongly enhances the targeting of Tmc1-GFP and Tmc2b-GFP to stereocilia. To identify the motifs of Tmie underlying the regulation of the Tmcs, we systematically deleted or replaced peptide segments. We then assessed localization and functional rescue of each mutated/chimeric form of Tmie in tmie mutants. We determined that the first putative helix was dispensable and identified a novel critical region of Tmie, the extracellular region and transmembrane domain, which is required for both mechanosensitivity and Tmc2b-GFP expression in bundles. Collectively, our results suggest that Tmie's role in sensory hair cells is to target and stabilize Tmc channel subunits to the site of MET.
跨膜内耳（TMIE）突变会导致人类耳聋；先前的研究表明，TMIE 参与了感觉毛细胞中的机械-电转导（MET）复合物，但 TMIE 的确切作用尚不清楚。在 tmie 斑马鱼突变体中，我们观察到 GFP 标记的 Tmc1 和 Tmc2b，它们是 MET 通道的亚基，不能靶向毛束。相比之下，Tmie 的过表达强烈增强了 Tmc1-GFP 和 Tmc2b-GFP 向静纤毛的靶向。为了确定 Tmie 调节 Tmcs 的基序，我们系统地删除或替换了肽段。然后，我们评估了每种突变/嵌合形式的 Tmie 在 tmie 突变体中的定位和功能挽救。我们确定第一个假定的螺旋是可有可无的，并确定了 Tmie 的一个新的关键区域，即细胞外区域和跨膜结构域，该区域对于机械敏感性和毛束中 Tmc2b-GFP 的表达都是必需的。总之，我们的结果表明，Tmie 在感觉毛细胞中的作用是将 Tmc 通道亚基靶向并稳定在 MET 位点。
