Brunet S, Polanski Z, Verlhac M H, Kubiak J Z, Maro B
Laboratoire de Biologie Cellulaire du Développement, Institut Jacques Monod, C.N.R.S., Université Paris 6, France.
Curr Biol. 1998 Nov 5;8(22):1231-4. doi: 10.1016/s0960-9822(07)00516-7.
Establishing a bipolar spindle is an early event of mitosis or meiosis. In somatic cells, the bipolarity of the spindle is predetermined by the presence of two centrosomes in prophase. Interactions between the microtubules nucleated by centrosomes and the chromosomal kinetochores enable the formation of the spindle. Non-specific chromatin is sufficient, however, to promote spindle assembly in Xenopus cell-free extracts that contain centrosomes [1,2]. The mouse oocyte represents an excellent model system in which to study the mechanism of meiotic spindle formation because of its size, transparency and slow development. These cells have no centrioles, and their multiple microtubule-organizing centers (MTOCs) are composed of foci of pericentriolar material [3,4]. The bipolarity of the meiotic spindle emerges from the reorganization of these randomly distributed MTOCs [4]. Regardless of the mechanisms involved in this reorganization, the chromosomes seem to have a major role during spindle formation in promoting microtubule polymerization and directing the appropriate rearrangement of MTOCs to form the two poles [5]. Here, we examined spindle formation in chromosome-free mouse oocyte fragments. We found that a bipolar spindle can form in vivo in the absence of any chromatin due to the establishment of interactions between microtubule asters that are progressively stabilized by an increase in the number of microtubules involved, demonstrating that spindle formation is an intrinsic property of the microtubule network.
建立双极纺锤体是有丝分裂或减数分裂的早期事件。在体细胞中，纺锤体的双极性在前期由两个中心体的存在预先决定。中心体产生的微管与染色体动粒之间的相互作用促使纺锤体形成。然而，在含有中心体的非洲爪蟾无细胞提取物中，非特异性染色质足以促进纺锤体组装[1,2]。小鼠卵母细胞因其大小、透明度和发育缓慢，是研究减数分裂纺锤体形成机制的极佳模型系统。这些细胞没有中心粒，其多个微管组织中心（MTOC）由中心粒周围物质的焦点组成[3,4]。减数分裂纺锤体的双极性源于这些随机分布的MTOC的重组[4]。无论这种重组涉及何种机制，染色体在纺锤体形成过程中似乎都起着主要作用，促进微管聚合并指导MTOC进行适当重排以形成两极[5]。在这里，我们研究了无染色体的小鼠卵母细胞片段中的纺锤体形成。我们发现，由于微管星状体之间相互作用的建立，双极纺锤体可以在没有任何染色质的情况下在体内形成，这种相互作用通过参与的微管数量增加而逐渐稳定，这表明纺锤体形成是微管网络的固有特性。
