Ben-Yosef Tamar, Belyantseva Inna A, Saunders Thomas L, Hughes Elizabeth D, Kawamoto Kohei, Van Itallie Christina M, Beyer Lisa A, Halsey Kärin, Gardner Donald J, Wilcox Edward R, Rasmussen Julia, Anderson James M, Dolan David F, Forge Andrew, Raphael Yehoash, Camper Sally A, Friedman Thomas B
Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville, MD 20850, USA.
Hum Mol Genet. 2003 Aug 15;12(16):2049-61. doi: 10.1093/hmg/ddg210.
Tight junctions (TJs) create ion-selective paracellular permeability barriers between extracellular compartments. In the organ of Corti of the inner ear, TJs of the reticular lamina separate K(+)-rich endolymph and Na(+)-rich perilymph. In humans, mutations of the gene encoding claudin 14 TJ protein cause profound deafness but the underlying pathogenesis is unknown. To explore the role of claudin 14 in the inner ear and in other tissues we created a mouse model by a targeted deletion of Cldn14. In the targeted allele a lacZ cassette is expressed under the Cldn14 promoter. In Cldn14-lacZ heterozygous mice beta-galactosidase activity was detected in cochlear inner and outer hair cells and supporting cells, in the collecting ducts of the kidney, and around the lobules of the liver. Cldn14-null mice have a normal endocochlear potential but are deaf due to rapid degeneration of cochlear outer hair cells, followed by slower degeneration of the inner hair cells, during the first 3 weeks of life. Monolayers of MDCK cells expressing claudin 14 show a 6-fold increase in the transepithelial electrical resistance by decreasing paracellular permeability for cations. In wild type mice, claudin 14 was immunolocalized at hair cell and supporting cell TJs. Our data suggest that the TJ complex at the apex of the reticular lamina requires claudin 14 as a cation-restrictive barrier to maintain the proper ionic composition of the fluid surrounding the basolateral surface of outer hair cells.
紧密连接（TJs）在细胞外间隙之间形成离子选择性的细胞旁通透性屏障。在内耳的柯蒂氏器中，网状板的紧密连接将富含钾离子的内淋巴和富含钠离子的外淋巴分隔开。在人类中，编码紧密连接蛋白14的基因突变会导致严重耳聋，但其潜在的发病机制尚不清楚。为了探究紧密连接蛋白14在内耳及其他组织中的作用，我们通过靶向缺失Cldn14创建了一个小鼠模型。在靶向等位基因中，一个lacZ盒在Cldn14启动子的控制下表达。在Cldn14-lacZ杂合小鼠中，在耳蜗内、外毛细胞及支持细胞、肾集合管以及肝小叶周围检测到了β-半乳糖苷酶活性。Cldn14基因敲除小鼠具有正常的内淋巴电位，但在出生后的前3周内，由于耳蜗外毛细胞迅速退化，随后内毛细胞缓慢退化，导致耳聋。表达紧密连接蛋白14的MDCK细胞单层通过降低阳离子的细胞旁通透性，使跨上皮电阻增加了6倍。在野生型小鼠中，紧密连接蛋白14免疫定位在毛细胞和支持细胞的紧密连接处。我们的数据表明，网状板顶端的紧密连接复合体需要紧密连接蛋白14作为阳离子限制屏障，以维持外毛细胞基底外侧表面周围液体的适当离子组成。
