Ahmed Zubair M, Goodyear Richard, Riazuddin Saima, Lagziel Ayala, Legan P Kevin, Behra Martine, Burgess Shawn M, Lilley Kathryn S, Wilcox Edward R, Riazuddin Sheikh, Griffith Andrew J, Frolenkov Gregory I, Belyantseva Inna A, Richardson Guy P, Friedman Thomas B
Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville, Maryland 20850, USA.
J Neurosci. 2006 Jun 28;26(26):7022-34. doi: 10.1523/JNEUROSCI.1163-06.2006.
Sound and acceleration are detected by hair bundles, mechanosensory structures located at the apical pole of hair cells in the inner ear. The different elements of the hair bundle, the stereocilia and a kinocilium, are interconnected by a variety of link types. One of these links, the tip link, connects the top of a shorter stereocilium with the lateral membrane of an adjacent taller stereocilium and may gate the mechanotransducer channel of the hair cell. Mass spectrometric and Western blot analyses identify the tip-link antigen, a hitherto unidentified antigen specifically associated with the tip and kinocilial links of sensory hair bundles in the inner ear and the ciliary calyx of photoreceptors in the eye, as an avian ortholog of human protocadherin-15, a product of the gene for the deaf/blindness Usher syndrome type 1F/DFNB23 locus. Multiple protocadherin-15 transcripts are shown to be expressed in the mouse inner ear, and these define four major isoform classes, two with entirely novel, previously unidentified cytoplasmic domains. Antibodies to the three cytoplasmic domain-containing isoform classes reveal that each has a different spatiotemporal expression pattern in the developing and mature inner ear. Two isoforms are distributed in a manner compatible for association with the tip-link complex. An isoform located at the tips of stereocilia is sensitive to calcium chelation and proteolysis with subtilisin and reappears at the tips of stereocilia as transduction recovers after the removal of calcium chelators. Protocadherin-15 is therefore associated with the tip-link complex and may be an integral component of this structure and/or required for its formation.
声音和加速度由毛束检测，毛束是位于内耳毛细胞顶端的机械感觉结构。毛束的不同组成部分，即静纤毛和动纤毛，通过多种连接类型相互连接。其中一种连接，即顶连接，将较短静纤毛的顶端与相邻较高静纤毛的侧膜相连，并可能控制毛细胞的机械转导通道。质谱分析和蛋白质印迹分析确定顶连接抗原，一种迄今未鉴定的抗原，它特异性地与内耳感觉毛束的顶连接和动纤毛连接以及眼睛光感受器的睫状萼相关，是人类原钙黏蛋白-15的鸟类直系同源物，原钙黏蛋白-15是1F型聋/盲乌舍尔综合征/DFNB23位点基因的产物。多种原钙黏蛋白-15转录本在小鼠内耳中表达，这些转录本定义了四个主要的异构体类别，其中两个具有全新的、以前未鉴定的胞质结构域。针对包含三个胞质结构域的异构体类别的抗体显示，每个异构体在发育中和成熟的内耳中都有不同的时空表达模式。两种异构体以与顶连接复合体相关联的方式分布。一种位于静纤毛顶端的异构体对钙螯合和枯草杆菌蛋白酶的蛋白水解敏感，并且在去除钙螯合剂后随着转导恢复而重新出现在静纤毛顶端。因此，原钙黏蛋白-15与顶连接复合体相关，可能是该结构的一个组成部分和/或其形成所必需的。
