Hirsch M S, Cook S C, Killiany R, Hartford Svoboda K K
Department of Anatomy and Neurobiology, Boston University School of Medicine, Massachusetts, USA.
Anat Rec. 1996 Mar;244(3):284-96. doi: 10.1002/(SICI)1097-0185(199603)244:3<284::AID-AR2>3.0.CO;2-Z.
Chondrocytes in specific areas of chick sterna have different developmental fates. Cephalic chondrocytes become hypertrophic and secrete type X collagen into the extracellular matrix, whereas middle and caudal chondrocytes remain cartilagenous throughout development, continuing to secrete collagen types II, IX, and XI. In this report, we ask if the cell size and cytoarchitecture of chondrocytes differ in cephalic, middle, and caudal portions of whole sterna prior to and during hypertrophy. In addition, what is the distribution of integrin subunits and actin associate proteins in differentiating chondrocytes?
Phalloidin was used to stain filamentous actin, and immunohistochemistry was used to localize the distribution of collagen molecules, integrin receptor subunits, and actin-associated proteins.
Chondrocytes stained for filamentous actin demonstrated that on day 14 cephalic chondrocytes had a significantly larger diameter than middle and caudal chondrocytes. Day 17 chondrocytes in nonhypertrophic cephalic and middle regions of sterna were significantly smaller than hypertrophic chondrocytes and significantly larger than caudal chondrocytes. In contrast to day 14 chondrocytes, day 17 chondrocytes in the hypertrophic region demonstrated similar diameters at all cartilagenous depths. The beta 1 integrin subunit appeared punctate and associated with cell membranes, allowing nonpolarized interactions with extracellular matrix molecules. The distribution of alpha integrin subunits was similar to the beta 1 integrin subunit, although alpha integrin subunits also appeared cytoplasmic. Actin-associated proteins, vinculin, and alpha-actinin, were associated with F-actin, but vinculin was more specifically localized to the ends of the actin filaments. Focal adhesion kinase was diffusely distributed throughout the cytoplasm but also demonstrated areas of colocalization with vinculin. Zyxin and paxillin demonstrated a punctate distribution, although paxillin was slightly more diffuse. Using immunohistochemical detection, no difference in integrin subunit or actin associated protein distribution could be determined between chondrocytes and hypertrophic chondrocytes.
The increased chondrocyte diameter observed in cephalic regions of sterna on day 14 suggests that intracellular changes may precede the specific hypertrophic marker, type X collagen, by several days. In addition, the presence of integrin subunits, which are known to interact with collagen and cytoskeletal proteins, suggests that communication may exist between chondrocytes and their extracellular matrix via these receptor molecules.
鸡胸骨特定区域的软骨细胞具有不同的发育命运。头部软骨细胞会肥大并向细胞外基质分泌X型胶原蛋白，而中部和尾部软骨细胞在整个发育过程中保持软骨状态，继续分泌II型、IX型和XI型胶原蛋白。在本报告中，我们探究在肥大之前及肥大过程中，整个胸骨的头部、中部和尾部的软骨细胞大小和细胞结构是否存在差异。此外，整合素亚基和肌动蛋白相关蛋白在分化软骨细胞中的分布情况如何？
使用鬼笔环肽对丝状肌动蛋白进行染色，并采用免疫组织化学方法定位胶原蛋白分子、整合素受体亚基和肌动蛋白相关蛋白的分布。
对丝状肌动蛋白染色的软骨细胞显示，在第14天，头部软骨细胞的直径明显大于中部和尾部软骨细胞。在第17天，胸骨非肥大头部和中部区域的软骨细胞明显小于肥大软骨细胞，且明显大于尾部软骨细胞。与第14天的软骨细胞不同，第17天肥大区域的软骨细胞在所有软骨深度的直径相似。β1整合素亚基呈点状并与细胞膜相关联，允许与细胞外基质分子进行非极化相互作用。α整合素亚基的分布与β1整合素亚基相似，不过α整合素亚基也出现在细胞质中。肌动蛋白相关蛋白、纽蛋白和α辅肌动蛋白与F-肌动蛋白相关，但纽蛋白更特异性地定位于肌动蛋白丝的末端。粘着斑激酶在整个细胞质中呈弥散分布，但也显示出与纽蛋白共定位的区域。桩蛋白和桩蛋白呈点状分布，不过桩蛋白的分布稍显弥散。通过免疫组织化学检测，未发现软骨细胞和肥大软骨细胞之间在整合素亚基或肌动蛋白相关蛋白分布上存在差异。
在第14天胸骨头部区域观察到的软骨细胞直径增加表明，细胞内变化可能比特定的肥大标志物X型胶原蛋白提前几天出现。此外，已知与胶原蛋白和细胞骨架蛋白相互作用的整合素亚基的存在表明，软骨细胞与其细胞外基质之间可能通过这些受体分子进行通讯。
