Tilney Lewis G, Connelly Patricia S, Ruggiero Linda, Vranich Kelly A, Guild Gregory M
Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6018, USA.
Mol Biol Cell. 2003 Oct;14(10):3953-66. doi: 10.1091/mbc.e03-03-0158. Epub 2003 Jul 25.
Drosophila bristle cells are shaped during growth by longitudinal bundles of cross-linked actin filaments attached to the plasma membrane. We used confocal and electron microscopy to examine actin bundle structure and found that during bristle elongation, snarls of uncross-linked actin filaments and small internal bundles also form in the shaft cytoplasm only to disappear within 4 min. Thus, formation and later removal of actin filaments are prominent features of growing bristles. These transient snarls and internal bundles can be stabilized by culturing elongating bristles with jasplakinolide, a membrane-permeant inhibitor of actin filament depolymerization, resulting in enormous numbers of internal bundles and uncross-linked filaments. Examination of bundle disassembly in mutant bristles shows that plasma membrane association and cross-bridging adjacent actin filaments together inhibits depolymerization. Thus, highly cross-bridged and membrane-bound actin filaments turn over slowly and persist, whereas poorly cross-linked filaments turnover more rapidly. We argue that the selection of stable bundles relative to poorly cross-bridged filaments can account for the size, shape, number, and location of the longitudinal actin bundles in bristles. As a result, filament turnover plays an important role in regulating cytoskeleton assembly and consequently cell shape.
果蝇刚毛细胞在生长过程中，通过附着于质膜的交联肌动蛋白丝纵向束来塑造形状。我们利用共聚焦显微镜和电子显微镜来检查肌动蛋白束的结构，发现刚毛伸长过程中，未交联的肌动蛋白丝缠结和小的内部束也仅在轴细胞质中形成，并在4分钟内消失。因此，肌动蛋白丝的形成和随后的去除是生长中刚毛的显著特征。通过用茉莉酸内酯（一种肌动蛋白丝解聚的膜渗透性抑制剂）培养伸长的刚毛，可以稳定这些短暂的缠结和内部束，从而产生大量的内部束和未交联的丝。对突变刚毛中束解聚的检查表明，质膜结合和相邻肌动蛋白丝的交联共同抑制了解聚。因此，高度交联且与膜结合的肌动蛋白丝周转缓慢并持续存在，而交联不良的丝周转更快。我们认为，相对于交联不良的丝，稳定束的选择可以解释刚毛中纵向肌动蛋白束的大小、形状、数量和位置。因此，丝周转在调节细胞骨架组装进而调节细胞形状方面起着重要作用。
