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

采用细胞剪切、旋转复制和荧光细胞化学技术研究了破骨细胞足状体中细胞骨架的组织结构。剪切后，在膜暴露的细胞质侧，留下与细胞骨架相关的网格蛋白斑块和颗粒。两种类型的肌动蛋白丝，这是确定的，即，在围绕足状体核心的部分中的相对长的细丝，和在核心中的高度分支的短细丝。单个肌动蛋白丝辐射的podosomes相互作用的几个膜颗粒沿着长度的细丝。这些颗粒沿着单个肌动蛋白丝的长度与膜表面进行许多侧向接触。肌动蛋白丝的极性在podosomes成为定向，使其倒刺的目的是针对核心的podosomes。肌动蛋白细胞骨架终止于或分支于足体，在足体处，膜与基质紧密粘附。微管通常不存在于足体结构中;然而，某些微管似乎在形态上与足体核心直接接触。大多数较大的网格蛋白斑块由网格蛋白网格的平片组成，所述网格蛋白网格将相邻的网格蛋白网格互连以形成广泛的网格蛋白区域。然而，小的深深陷入网格蛋白斑块和podosomal细胞骨架位于靠近在一起。因此，这些观察结果表明，网格蛋白斑块腹膜破骨细胞可能参与细胞粘附和受体配体复合物的形成。

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.