Guild Gregory M, Connelly Patricia S, Ruggiero Linda, Vranich Kelly A, Tilney Lewis G
Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA.
J Cell Biol. 2003 Sep 15;162(6):1069-77. doi: 10.1083/jcb.200305143.
The actin bundles essential for Drosophila bristle elongation are hundreds of microns long and composed of cross-linked unipolar filaments. These long bundles are built from much shorter modules that graft together. Using both confocal and electron microscopy, we demonstrate that newly synthesized modules are short (1-2 microm in length); modules elongate to approximately 3 microm by growing over the surface of longitudinally adjacent modules to form a graft; the grafted regions are initially secured by the forked protein cross-bridge and later by the fascin cross-bridge; actin bundles are smoothed by filament addition and appear continuous and without swellings; and in the absence of grafting, dramatic alterations in cell shape occur that substitutes cell width expansion for elongation. Thus, bundle morphogenesis has several components: module formation, elongation, grafting, and bundle smoothing. These actin bundles are much like a rope or cable, made by overlapping elements that run a small fraction of the overall length, and stiffened by cross-linking.
对于果蝇刚毛伸长至关重要的肌动蛋白束长达数百微米，由交联的单极丝组成。这些长束由短得多的模块拼接而成。利用共聚焦显微镜和电子显微镜，我们证明新合成的模块很短（长度为1 - 2微米）；模块通过在纵向相邻模块的表面生长以形成嫁接而伸长至约3微米；嫁接区域最初由叉状蛋白交叉桥固定，随后由肌动蛋白结合蛋白交叉桥固定；肌动蛋白束通过添加细丝而变得平滑，呈现出连续且无肿胀的状态；并且在没有嫁接的情况下，会发生显著的细胞形态改变，即细胞宽度扩展替代了伸长。因此，束形态发生有几个组成部分：模块形成、伸长、嫁接和束平滑。这些肌动蛋白束很像一根绳子或缆绳，由覆盖总长度一小部分的重叠元件制成，并通过交联而变硬。
