Mogensen M M, Tucker J B, Stebbings H
Department of Biology and Preclinical Medicine, University of St. Andrews, Fife, Scotland.
J Cell Biol. 1989 Apr;108(4):1445-52. doi: 10.1083/jcb.108.4.1445.
Hook decoration with pig brain tubulin was used to assess the polarity of microtubules which mainly have 15 protofilaments in the transcellular bundles of late pupal Drosophila wing epidermal cells. The microtubules make end-on contact with cell surfaces. Most microtubules in each bundle exhibited a uniform polarity. They were oriented with their minus ends associated with their hemidesmosomal anchorage points at the apical cuticle-secreting surfaces of the cells. Plus ends were directed towards, and were sometimes connected to, basal attachment desmosomes at the opposite ends of the cells. The orientation of microtubules at cell apices, with minus ends directed towards the cell surface, is opposite to the polarity anticipated for microtubules which have elongated centrifugally from centrosomes. It is consistent, however, with evidence that microtubule assembly is nucleated by plasma membrane-associated sites at the apical surfaces of the cells (Mogensen, M. M., and J. B. Tucker. 1987. J. Cell Sci. 88:95-107) after these cells have lost their centriole-containing, centrosomal, microtubule-organizing centers (Tucker, J. B., M. J. Milner, D. A. Currie, J. W. Muir, D. A. Forrest, and M.-J. Spencer. 1986. Eur. J. Cell Biol. 41:279-289). Our findings indicate that the plus ends of many of these apically nucleated microtubules are captured by the basal desmosomes. Hence, the situation may be analogous to the polar-nucleation/chromosomal-capture scheme for kinetochore microtubule assembly in mitotic and meiotic spindles. The cell surface-associated nucleation-elongation-capture mechanism proposed here may also apply during assembly of transcellular microtubule arrays in certain other animal tissue cell types.
用猪脑微管蛋白进行钩状装饰，以评估微管的极性。在果蝇蛹后期翅表皮细胞的跨细胞束中，微管主要由15根原纤维组成。微管与细胞表面进行端对端接触。每个束中的大多数微管呈现出统一的极性。它们的负极与细胞顶端角质层分泌表面的半桥粒锚定点相连。正极指向细胞相对端的基底附着桥粒，有时还与之相连。细胞顶端微管的取向是负极朝向细胞表面，这与从中心体离心伸长的微管所预期的极性相反。然而，这与以下证据一致：在这些细胞失去含中心粒的、中心体的微管组织中心后（塔克，J.B.，M.J.米尔纳，D.A.柯里，J.W.缪尔，D.A.福雷斯特，和M.-J.斯宾塞。1986.欧洲细胞生物学杂志。41:279-289），微管组装由细胞顶端表面与质膜相关的位点成核（莫根森，M.M.，和J.B.塔克。1987.细胞科学杂志。88:95-107）。我们的研究结果表明，许多这些顶端成核的微管的正极被基底桥粒捕获。因此，这种情况可能类似于有丝分裂和减数分裂纺锤体中动粒微管组装的极核形成/染色体捕获模式。这里提出的细胞表面相关的成核-伸长-捕获机制也可能适用于某些其他动物组织细胞类型中跨细胞微管阵列的组装过程。
