Höfer D, Drenckhahn D
Institute of Anatomy, Julius-Maximilians-University Würzburg, Germany.
Anat Rec. 1996 May;245(1):57-64. doi: 10.1002/(SICI)1097-0185(199605)245:1<57::AID-AR10>3.0.CO;2-8.
Stereocilia of the human ductus epididymidis and ductus deferens display unique features in that they arise from an apical cell protrusion (hillock) and contain thick stem portions which are interconnected by cytoplasmic bridges. The molecular basis for this unique fusion and branching pattern is hitherto unknown. These morphologic specialties led us to study the cytoskeleton of male spermway stereocilia with respect to the major proteins that constitute the supportive cytoskeleton of intestinal microvilli and inner ear stereocilia.
Samples of the human epididymidis and ductus deferens were studied by immunoblotting and immunocytochemistry at the light and electron microscope levels.
Spermway stereocilia are supported by an internal actin filament bundle crosslinked by fimbrin and associated with the membrane linker molecule ezrin. The stem portions and hillock area are supplied with the crossbridge forming molecule alpha-actinin. Spermway stereocilia differ from brush border microvilli of the intestine, kidney, and ductuli efferentes by the lack of the second bundling protein villin and the unusual expression of alpha-actinin in the stem region. They resemble inner ear stereocilia by the presence of fimbrin and absence of villin, but differ from them by expression of ezrin and alpha-actinin. Thus, the main molecular difference between spermway stereocilia and stereocilia/microvilli of other locations is the presence of alpha-actinin in their stem portion and the hillock area.
Since alpha-actinin can form crossbridges between adjacent actin filaments (bundles) at longer distances than the other crosslinker of the stereocilium core bundle, fimbrin, we assume that alpha-actinin is essential for both the formation of the stem portions of spermway stereocilia and for the generation of their striking branching pattern. A developmentally regulated temporal sequence of expression of fimbrin and alpha-actinin might control the unique architecture of spermway stereocilia.
人类附睾管和输精管的静纤毛具有独特特征，它们起源于顶端细胞突起（小丘），并包含由细胞质桥相互连接的粗大茎部。这种独特融合和分支模式的分子基础迄今尚不清楚。这些形态学特征促使我们研究男性输精管道静纤毛的细胞骨架，涉及构成肠道微绒毛和内耳静纤毛支持性细胞骨架的主要蛋白质。
通过免疫印迹以及光镜和电镜水平的免疫细胞化学研究人类附睾和输精管样本。
输精管道静纤毛由内部肌动蛋白丝束支撑，该丝束由丝束蛋白交联，并与膜连接分子埃兹蛋白相关联。茎部和小丘区域含有形成交叉桥的分子α - 辅肌动蛋白。输精管道静纤毛与肠道、肾脏和输出小管的刷状缘微绒毛不同，缺乏第二种成束蛋白绒毛蛋白，且α - 辅肌动蛋白在茎区域有异常表达。它们与内耳静纤毛相似之处在于存在丝束蛋白且缺乏绒毛蛋白，但在埃兹蛋白和α - 辅肌动蛋白的表达上与之不同。因此，输精管道静纤毛与其他部位静纤毛/微绒毛之间的主要分子差异在于其茎部和小丘区域存在α - 辅肌动蛋白。
由于α - 辅肌动蛋白能够在比静纤毛核心束的另一种交联蛋白丝束蛋白更长的距离上在相邻肌动蛋白丝（束）之间形成交叉桥，我们推测α - 辅肌动蛋白对于输精管道静纤毛茎部的形成及其显著分支模式的产生至关重要。丝束蛋白和α - 辅肌动蛋白表达的发育调控时间序列可能控制着输精管道静纤毛的独特结构。
