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蛋白酪氨酸磷酸酶受体Q在静纤毛近端的动态区室化:基于肌球蛋白VI的转运的意义

Dynamic compartmentalization of protein tyrosine phosphatase receptor Q at the proximal end of stereocilia: implication of myosin VI-based transport.

作者信息

Sakaguchi Hirofumi, Tokita Joshua, Naoz Moshe, Bowen-Pope Daniel, Gov Nir S, Kachar Bechara

机构信息

Section on Structural Cell Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, USA. hiro-s @koto.kpu- m.ac.jp

出版信息

Cell Motil Cytoskeleton. 2008 Jul;65(7):528-38. doi: 10.1002/cm.20275.

Abstract

Hair cell stereocilia are apical membrane protrusions filled with uniformly polarized actin filament bundles. Protein tyrosine phosphatase receptor Q (PTPRQ), a membrane protein with extracellular fibronectin repeats has been shown to localize at the stereocilia base and the apical hair cell surface, and to be essential for stereocilia integrity. We analyzed the distribution of PTPRQ and a possible mechanism for its compartmentalization. Using immunofluorescence we demonstrate that PTPRQ is compartmentalized at the stereocilia base with a decaying gradient from base to apex. This distribution can be explained by a model of transport directed toward the stereocilia base, which counteracts diffusion of the molecules. By mathematical analysis, we show that this counter transport is consistent with the minus end-directed movement of myosin VI along the stereocilia actin filaments. Myosin VI is localized at the stereocilia base, and exogenously expressed myosin VI and PTPRQ colocalize in the perinuclear endosomes in COS-7 cells. In myosin VI-deficient mice, PTPRQ is distributed along the entire stereocilia. PTPRQ-deficient mice show a pattern of stereocilia disruption that is similar to that reported in myosin VI-deficient mice, where the predominant features are loss of tapered base, and fusion of adjacent stereocilia. Thin section and freeze-etching electron microscopy showed that localization of PTPRQ coincides with the presence of a dense cell surface coat. Our results suggest that PTPRQ and myosin VI form a complex that dynamically maintains the organization of the cell surface coat at the stereocilia base and helps maintain the structure of the overall stereocilia bundle.

摘要

毛细胞静纤毛是充满均匀极化肌动蛋白丝束的顶端膜突起。蛋白酪氨酸磷酸酶受体Q(PTPRQ)是一种具有细胞外纤连蛋白重复序列的膜蛋白,已被证明定位于静纤毛基部和毛细胞顶端表面,并且对静纤毛的完整性至关重要。我们分析了PTPRQ的分布及其分区的可能机制。利用免疫荧光我们证明,PTPRQ在静纤毛基部呈分区分布,从基部到顶端呈衰减梯度。这种分布可以用一种朝向静纤毛基部的运输模型来解释,该模型抵消了分子的扩散。通过数学分析,我们表明这种反向运输与肌球蛋白VI沿静纤毛肌动蛋白丝的负端定向运动一致。肌球蛋白VI定位于静纤毛基部,外源性表达的肌球蛋白VI和PTPRQ在COS-7细胞的核周内体中共定位。在肌球蛋白VI缺陷小鼠中,PTPRQ沿整个静纤毛分布。PTPRQ缺陷小鼠表现出与肌球蛋白VI缺陷小鼠报道的类似的静纤毛破坏模式,其主要特征是锥形基部丧失和相邻静纤毛融合。超薄切片和冷冻蚀刻电子显微镜显示,PTPRQ的定位与致密细胞表面被膜的存在一致。我们的结果表明,PTPRQ和肌球蛋白VI形成一个复合物,动态维持静纤毛基部细胞表面被膜的组织,并有助于维持整个静纤毛束的结构。

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