Osteoclasts (OCs) can adhere to a variety of substrate surfaces by highly dynamic actin‐based cytoskeletal structures termed podosomes. This tight attachment is established by a sealing zone (SZ), which is made of interconnected individual podosomes. Compared with scattered podosomes in various cell types, the architecture of the SZ is still unclear. Especially, ultrastructural studies on the details of the cytoskeletal structure of an OC have been challenging, because the high density of filaments in their podosomes obscure visualization of individual filaments. Therefore, to study this organization in more exact detail, we employed shearing open combined with replica electron microscopy. The present study provides several new details of the podosome and SZ structure, which were previously unrecognized: (a) the SZ consists of recognizable podosomes with a dense actin network of interpodosomal regions characterized by multiple layers of crossing, branching and anastomosing actin filament networks; (b) the Arp2/3 complex is distributed throughout the actin network of podosomes and SZ, indicating that actin polymerization is concentrated at these regions; (c) a close spatial relationship between the podosome and the dorsal membrane; and (d) a network of membranous organelles in close proximity to the podosomes in the SZ. Taken together, the present study reveals that a more complicated interpodosomal actin network among neighboring individual podosomes, which is more complicated than previously thought, appears to form the SZ. Indeed, individual podosomes are not an isolated structural unit from other organelles; and, in turn, their dynamism might affect the surrounding interpodosomal cytoskeletons, membranous organelles, and plasma membrane.

中文翻译：

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通过细胞剪切，快速冷冻和铂复制电子显微镜观察发现，散布的足小体和与培养的破骨细胞的密封区结构相关的足小体。

破骨细胞（OCs）可以通过高度动态的基于肌动蛋白的细胞骨架结构（称为足小体）粘附在多种基质表面上。这种紧密的连接是由一个密封区域（SZ）建立的，该区域由相互连接的单个足小体构成。与各种细胞类型中分散的足小体相比，SZ的结构仍不清楚。尤其是，有关OC的细胞骨架结构细节的超微结构研究颇具挑战性，因为其足小体中细丝的高密度掩盖了单个细丝的可视化。因此，为了更精确地研究该组织，我们采用剪切开孔与复制电子显微镜相结合的方法。本研究提供了脚架和SZ结构的一些新细节，这些细节以前是无法识别的：（a）SZ由可辨认的足小体组成，该足小体具有致密的肌间体区域肌动蛋白网络，其特征是多层交叉，分支和吻合肌动蛋白丝网络；（b）Arp2 / 3复合物分布在整个足小体和SZ的肌动蛋白网络中，表明肌动蛋白的聚合集中在这些区域；（c）足小体和背膜之间紧密的空间关系；（d）靠近深圳足部的膜细胞器网络。综上所述，本研究表明，相邻个体足小体之间的更复杂的足小体肌动蛋白网络似乎比以前认为的要复杂，形成了SZ。的确，单个足小体不是与其他细胞器分离的结构单位。然后，