Mogensen M M, Malik A, Piel M, Bouckson-Castaing V, Bornens M
Department of Anatomy and Physiology, MSI/WTB complex, Dow Street, University of Dundee, Dundee, DD1 5EH, UK.
J Cell Sci. 2000 Sep;113 ( Pt 17):3013-23. doi: 10.1242/jcs.113.17.3013.
The novel concept of a centrosomal anchoring complex, which is distinct from the gamma-tubulin nucleating complex, has previously been proposed following studies on cochlear epithelial cells. In this investigation we present evidence from two different cell systems which suggests that the centrosomal protein ninein is a strong candidate for the proposed anchoring complex. Ninein has recently been observed in cultured fibroblast cells to localise primarily to the post-mitotic mother centriole, which is the focus for a classic radial microtubule array. We show here by immunoelectron microscopical analyses of centrosomes from mouse L929 cells that ninein concentrates at the appendages surrounding the mother centriole and at the microtubule minus-ends. We further show that localisation of ninein in the cochlear supporting epithelial cells, where the vast majority of the microtubule minus-ends are associated with apical non-centrosomal sites, suggests that it is not directly involved in microtubule nucleation. Ninein seems to play an important role in the positioning and anchorage of the microtubule minus-ends in these epithelial cells. Evidence is presented which suggests that ninein is released from the centrosome, translocated with the microtubules, and is responsible for the anchorage of microtubule minus-ends to the apical sites. We propose that ninein is a non-nucleating microtubule minus-end associated protein which may have a dual role as a minus-end capping and anchoring protein.
在对耳蜗上皮细胞进行研究之后，先前曾提出过一种与γ-微管蛋白成核复合体不同的中心体锚定复合体的新概念。在本研究中，我们展示了来自两种不同细胞系统的证据，这些证据表明中心体蛋白九蛋白是所提出的锚定复合体的有力候选者。最近在培养的成纤维细胞中观察到九蛋白主要定位于有丝分裂后的母中心粒，而母中心粒是经典放射状微管阵列的焦点。我们通过对小鼠L929细胞中心体的免疫电子显微镜分析表明，九蛋白集中在围绕母中心粒的附属结构以及微管负端。我们进一步表明，在耳蜗支持上皮细胞中，绝大多数微管负端与顶端非中心体部位相关，九蛋白在其中的定位表明它不直接参与微管成核。九蛋白似乎在这些上皮细胞中微管负端的定位和锚定中发挥重要作用。有证据表明，九蛋白从中心体释放，随微管转运，并负责将微管负端锚定到顶端部位。我们提出九蛋白是一种非成核的微管负端相关蛋白，可能具有作为负端封端蛋白和锚定蛋白的双重作用。
