Adhesion structures and their cytoskeleton-membrane interactions at podosomes as a specific signal transduction site of osteoclasts

用细胞剪切、旋转复制和荧光细胞化学技术研究了破骨细胞足体中细胞骨架的组织。剪毛后，在细胞膜暴露的细胞质一侧，留下与细胞骨架相关的笼状蛋白斑块和颗粒。足体的细胞骨架具有两种类型的肌动蛋白细丝，即位于足体核心周围的相对较长的细丝和位于核心的高度分枝的短丝。从足体发出的单个肌动蛋白细丝与沿细丝长度方向的几个膜颗粒相互作用。这些颗粒沿着单个肌动蛋白细丝的长度与膜表面进行了多次横向接触。足体中肌动蛋白细丝的极性变得定向，其带刺的末端指向足体的核心。肌动蛋白细胞骨架在足体终止或分叉，膜与底物紧密附着。微管通常不存在于足体结构中，但某些微管在形态上似乎与足体核心直接接触。大多数较大的网状蛋白斑块由扁平的网状网状结构组成，这些网状网状结构将相邻的网状网状结构相互连接，形成一个广泛的网状结构区域。但深陷的网状蛋白小斑块与胞体后骨架紧密相连。因此，这些观察结果表明，破骨细胞腹膜上的网状蛋白斑块可能参与了细胞黏附和受体-配体复合体的形成。

Organization of the cytoskeleton in podosomes of osteoclasts was studied by use of cell shearing, rotary replication, and fluorescence cytochemical techniques. After shearing, on the exposed cytoplasmic side of the membrane, clathrin plaques and particles associated with the cytoskeleton were left behind. The cytoskeleton of the podosomes was characterized by two types of actin filaments, which were identified, i.e., relatively long filaments in the portion surrounding the podosome core, and highly branched short filaments in the core. Individual actin filaments radiating from the podosomes interacted with several membrane particles along the length of the filaments. Many lateral contacts with the membrane surface by the particles were made along the length of individual actin filaments. The polarity of actin filaments in podosomes became oriented such that their barbed ends were directed towards the core of podosomes. The actin cytoskeletons terminated or branched at the podosomes, where the membrane tightly adhered to the substratum. Microtubules were not composed of usually present in the podosome structures ; however, certain microtubules appeared to be morphologically in direct contact with the podosome core. Most of the larger clathrin plaques consisted of flat sheets of clathrin lattices that interconnected neighboring clathrin lattices to form an extensive clathrin area. However, the small deeply invaginated clathrin plaques and the podosomal cytoskeleton were located close together. Consequently, these observations indicate that the clathrin plaques on the ventral membrane of osteoclasts might be involved in both cell adhesion and formation of receptor-ligand complexes.