Lo W K, Shaw A P, Wen X J
Department of Anatomy, Morehouse School of Medicine, 720 Westview Drive, SW, Atlanta, GA 30310, USA.
Exp Eye Res. 1997 Nov;65(5):691-701. doi: 10.1006/exer.1997.0375.
The distribution and organization of actin filament bundles were studied in cortical fiber cells of rat lenses at various ages (3 days to 2.5 months old), using thin-section electron microscopy, immunocytochemistry and immunoblotting. Electron microscopy showed that actin bundles were regularly found along cortical fiber cell membranes of the lens at all ages studied. The actin bundles were commonly arranged in three distinct units, one bundle in each fiber cell, located at the intersections where three hexagonal fiber cells meet as seen in cross sections. These actin bundles were approximately 150 nm in diameter and were composed of 7-nm small filaments. They were aligned parallel to the long axis of fiber cells as judged by both cross and longitudinal sections. The outside border of each bundle was always surrounded by a zone of 10-nm intermediate filaments which have the same orientation as that of the actin bundles. In longitudinal sections, elongated actin bundles were always parallel to the cell membranes. A number of individual actin bundles sometimes were found to form a chain with periodic short intervals. In addition, actin bundles were frequently associated with adherens junctions near the intersections and other regions of fiber cell membranes. By immunoelectron microscopy, we demonstrated that these filament bundles indeed contained actins. By rhodamine-phalloidin labelling, we found that labeled actin bundles appeared as large, distinct dots at the corners of hexagonal fiber cells in all ages studied. In addition, non-bundle F-actins were labeled preferentially along the cell membranes of the short sides of hexagonal fiber cells. This resulted in a unique zigzag pattern of actin labeling commonly seen in the cortical fiber cells of a mature rat lens. Finally, we showed that alpha-actinin was associated with the actin bundles in the fiber cells by immunofluorescent double labeling and immunoblotting. It is suggested that this unique arrangement of actin bundles in fiber cells may provide a stabilizing structure for forming a sharp angle at each corner of fiber cells, thereby the hexagonal shape of the cells can be maintained.
利用超薄切片电子显微镜、免疫细胞化学和免疫印迹技术，研究了不同年龄（3天至2.5个月大）大鼠晶状体皮质纤维细胞中肌动蛋白丝束的分布和组织情况。电子显微镜显示，在所研究的所有年龄段的晶状体中，肌动蛋白丝束均规则地分布在皮质纤维细胞膜周围。肌动蛋白丝束通常排列成三个不同的单元，每个纤维细胞中有一束，位于三个六边形纤维细胞相交的交叉点处，如在横截面中所见。这些肌动蛋白丝束直径约为150纳米，由7纳米的细丝组成。通过横截面和纵截面判断，它们与纤维细胞的长轴平行排列。每个丝束的外边界总是被一个10纳米的中间丝区域包围，这些中间丝与肌动蛋白丝束的方向相同。在纵截面中，细长的肌动蛋白丝束总是与细胞膜平行。有时会发现许多单独的肌动蛋白丝束形成一条具有周期性短间隔的链。此外，肌动蛋白丝束经常与纤维细胞膜交叉点附近和其他区域的黏附连接相关联。通过免疫电子显微镜，我们证明这些丝束确实含有肌动蛋白。通过罗丹明 - 鬼笔环肽标记，我们发现在所研究的所有年龄段中，标记的肌动蛋白丝束在六边形纤维细胞的角处呈现为大的、明显的点。此外，非丝束F - 肌动蛋白优先沿着六边形纤维细胞短边的细胞膜被标记。这导致了在成熟大鼠晶状体皮质纤维细胞中常见的独特的锯齿状肌动蛋白标记模式。最后，我们通过免疫荧光双标记和免疫印迹表明，α - 辅肌动蛋白与纤维细胞中的肌动蛋白丝束相关联。有人认为，纤维细胞中肌动蛋白丝束的这种独特排列可能为在纤维细胞的每个角处形成锐角提供一种稳定结构，从而维持细胞的六边形形状。
