The physical structure of the extracellular matrix (ECM) is tissue-specific and fundamental to normal tissue function. Proper alignment of ECM fibers is essential for the function of a variety of tissues. While matrix assembly in general has been intensively investigated, little is known about the mechanisms required for formation of aligned ECM fibrils. We investigated the initiation of fibronectin (FN) matrix assembly using fibroblasts that assemble parallel ECM fibrils and found that matrix assembly sites, where FN fibrillogenesis is initiated, were oriented in parallel at the cell poles. We show that these polarized matrix assembly sites progress into fibrillar adhesions and ultimately into aligned FN fibrils. Cells that assemble an unaligned, meshwork matrix formed matrix assembly sites around the cell periphery but the distribution of matrix assembly sites in these cells could be modulated through micropatterning or mechanical stretch. While an elongated cell shape corresponds with a polarized matrix assembly site distribution, these two features are not absolutely linked since we discovered that transforming growth factor beta (TGF-β1) enhances matrix assembly site polarity and assembly of aligned fibrils independently of cell elongation. We conclude the ultimate orientation of FN fibrils is determined by the alignment and distribution of matrix assembly sites which form during the initial stages of cell-FN interactions.

细胞外基质 (ECM) 的物理结构是组织特异性的，是正常组织功能的基础。ECM 纤维的正确排列对于各种组织的功能至关重要。虽然总体上已经对基质组装进行了深入研究，但对形成对齐的 ECM 原纤维所需的机制知之甚少。我们使用组装平行 ECM 原纤维的成纤维细胞研究了纤连蛋白 (FN) 基质组装的启动，发现启动 FN 原纤维生成的基质组装位点在细胞极平行定向。我们表明这些极化的矩阵组装位点进展为纤维状粘连，并最终形成对齐的 FN 纤维。组装未对齐的细胞，网状矩阵在细胞外围形成矩阵组装位点，但这些细胞中矩阵组装位点的分布可以通过微图案化或机械拉伸进行调节。虽然细长的细胞形状与极化的基质组装位点分布相对应，但这两个特征并不是绝对相关的，因为我们发现转化生长因子 β (TGF-β1) 增强了基质组装位点极性和对齐原纤维的组装，而与细胞伸长无关。我们得出结论，FN 原纤维的最终方向是由在细胞-FN 相互作用的初始阶段形成的基质组装位点的排列和分布决定的。虽然细长的细胞形状与极化的基质组装位点分布相对应，但这两个特征并不是绝对相关的，因为我们发现转化生长因子 β (TGF-β1) 增强了基质组装位点极性和对齐原纤维的组装，而与细胞伸长无关。我们得出结论，FN 原纤维的最终方向是由在细胞-FN 相互作用的初始阶段形成的基质组装位点的排列和分布决定的。虽然细长的细胞形状与极化的基质组装位点分布相对应，但这两个特征并不是绝对相关的，因为我们发现转化生长因子 β (TGF-β1) 增强了基质组装位点极性和对齐原纤维的组装，而与细胞伸长无关。我们得出结论，FN 原纤维的最终方向是由在细胞-FN 相互作用的初始阶段形成的基质组装位点的排列和分布决定的。