Department of Ear Nose & Throat, Third Hospital and Bethune International Peace Hospital of Hebei Medical University, Shijiazhuang, Hebei, People's Republic of China.
Biochem Biophys Res Commun. 2012 Jan 6;417(1):245-50. doi: 10.1016/j.bbrc.2011.11.093. Epub 2011 Nov 28.
Mutations in Gjb2 and Gjb6 genes, coding for connexin26 (Cx26) and Cx30 proteins, respectively, are linked to about half of all cases of human autosomal non-syndromic prelingual deafness. Molecular mechanisms of the hearing impairments, however, are unclear. Most cochlear gap junctions (GJs) are co-assembled from Cx26 and Cx30 and deletion of either one of them causes deafness. Our previous studies have shown that normal hearing is possible in the absence of the Cx30 gene when Cx26 is over-expressed. To further test unique functional requirements for various types of connexins in the hearing, we investigated whether the hearing in the conditional Cx26 (cCx26) null mice could be rescued by genetically over-expressing Cx30. Multiple lines of control and experimental mouse models were used. Auditory brainstem response (ABR) measurements showed normal hearing in targeted gene deletion mice when the deleted Cx26 or Cx30 was transgenically expressed from integrated bacterial artificial chromosome (BAC), demonstrating the effectiveness of the BAC rescue approach. In contrast, severe hearing loss was found in cCx26 null mice in which Cx30 was over-expressed. Morphology observations were consistent with the ABR data. Cochleae of cCx26 null mice with and without the transgenic over-expression of Cx30 both showed the typical immature feature of postnatal cochlear development-the closed tunnel of Corti. Immunolabeling data and Western blot quantification indicated that the Cx26 protein expression preceded that of Cx30 during the early postnatal period in the cochlea. Null expression of Cx26 may therefore uniquely result in a transient period when a total elimination of GJs in functionally-important regions of the developing cochlea is possible. We conclude that Cx26 plays an essential role in the development of the auditory sensory epithelium and its unique developmental functions required for normal hearing is not replaceable by Cx30.
Gjb2 和 Gjb6 基因突变分别导致连接蛋白 26（Cx26）和 Cx30 蛋白，这两种蛋白与大约一半的人类常染色体非综合征性先天性耳聋有关。然而，听力损伤的分子机制尚不清楚。大多数耳蜗缝隙连接（GJ）是由 Cx26 和 Cx30 共同组装而成的，其中任何一种缺失都会导致耳聋。我们之前的研究表明，当 Cx26 过表达时，即使没有 Cx30 基因，正常听力也是可能的。为了进一步测试各种连接蛋白在听力中的独特功能要求，我们研究了条件性 Cx26（cCx26）缺失小鼠的听力是否可以通过基因过表达 Cx30 来挽救。使用了多种对照和实验小鼠模型。听觉脑干反应（ABR）测量显示，当缺失的 Cx26 或 Cx30 从整合的细菌人工染色体（BAC）中转基因表达时，靶向基因缺失小鼠的听力正常，这证明了 BAC 挽救方法的有效性。相比之下，在过表达 Cx30 的 cCx26 缺失小鼠中发现了严重的听力损失。形态学观察与 ABR 数据一致。cCx26 缺失小鼠耳蜗，无论是否过表达 Cx30，均显示出生后耳蜗发育的典型不成熟特征——柯蒂氏管的封闭隧道。免疫标记数据和 Western blot 定量分析表明，在耳蜗中，Cx26 蛋白的表达先于 Cx30 表达。因此，Cx26 的缺失可能会导致功能性重要区域 GJ 的完全消除，从而导致一个短暂的时期。我们得出结论，Cx26 在听觉感觉上皮的发育中发挥着重要作用，其独特的发育功能是 Cx30 无法替代的。
