Membrane associated clathrin sheets as a possible adhesion structure in cultured osteoclasts

本研究的目的是利用免疫荧光显微镜和电镜观察细胞剪切或洗涤剂提取后培养的破骨细胞的细胞-基质粘附结构。鉴定出两种不同的粘附结构；一个是典型的足粒体，另一个是网格蛋白片。速冻和冷冻替代或冷冻干燥的网格蛋白呈典型的蜂窝状亚结构，由六边形或五边形的多边形组成（每个多边形直径为20 ~ 30nm）。这些网格蛋白片经常出现在腹膜的周围或中心区域。网格蛋白片几乎没有细胞骨架，而足小体则由微丝束和相关结构组成。在某些情况下，运动中的破骨细胞假基的腹侧膜含有几个网格蛋白片。此外，即使在用机械细胞剪切和化学洗涤剂萃取几乎去除细胞结构后，网格蛋白片仍留在细胞表面。总之，这些结果支持了网格蛋白片通过受体-配体相互作用在破骨细胞粘附中可能起作用的观点。

The purpose of the present study is to investigate the cell-substratum adhesion structures in cultured osteoclasts using immunofluorescent microscopy and electron microscopy after cell shearing or detergent extraction. Two different adhesion structures were identified ; one was typical podosomes and the other clathrin sheets. In quick-freezing and freeze-substituted or freeze-dried replicas the clathrins showed a typical honey-comb substructure which were composed of polygons with hexagonal or pentagonal in shape (each polygon was 20〜30nm in diameter). These clathrin sheets were often encountered the peripheral or central region of the ventral membrane. Almost clathrin sheets were devoid of the cytoskeletons, while podosomes were composed of the bundles of microfilaments and related structures. In some case, the ventral membrane of pseudo-podium in moving osteoclasts contained several clathrin sheets. In addition clathrin sheets were left behind the cell surface even after almost cellular structures had removed away by using mechanical cell shearing and chemical detergent extraction. In conclusion, these results, therefore, support the idea that the clathrin sheets plays a possible role in osteoclastic adhesion via receptor-ligand interaction.