Experimental Center, Faculty of Medicine Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany.
Experimental Center, Faculty of Medicine Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany.
Curr Biol. 2018 Sep 24;28(18):2991-2997.e2. doi: 10.1016/j.cub.2018.07.012. Epub 2018 Sep 6.
In oocytes of many organisms, meiotic spindles form in the absence of centrosomes [1-5]. Such female meiotic spindles have a pointed appearance in metaphase with microtubules focused at acentrosomal spindle poles. At anaphase, the microtubules of acentrosomal spindles then transition to an inter-chromosomal array, while the spindle poles disappear. This transition is currently not understood. Previous studies have focused on this inter-chromosomal microtubule array and proposed a pushing model to drive chromosome segregation [6, 7]. This model includes an end-on orientation of microtubules with chromosomes. Alternatively, chromosomes were thought to associate along bundles of microtubules [8, 9]. Starting with metaphase, this second model proposed a pure lateral chromosome-to-microtubule association up to the final meiotic stages of anaphase. Here, we applied large-scale electron tomography [10] of staged C. elegans oocytes in meiosis to analyze the orientation of microtubules in respect to chromosomes. We show that microtubules at metaphase I are primarily oriented laterally to the chromosomes and that microtubules switch to an end-on orientation during progression through anaphase. We further show that this switch in microtubule orientation involves a kinesin-13 microtubule depolymerase, KLP-7, which removes laterally associated microtubules around chromosomes. From this, we conclude that both lateral and end-on modes of microtubule-to-chromosome orientations are successively used in C. elegans oocytes to segregate meiotic chromosomes.
在许多生物体的卵母细胞中，有丝分裂纺锤体在没有中心体的情况下形成[1-5]。这种雌性有丝分裂纺锤体在中期呈尖状，微管集中在无中心体纺锤体极。在后期，无中心体纺锤体的微管然后过渡到染色体间阵列，而纺锤体极消失。目前尚不清楚这种转变。以前的研究集中在这个染色体间微管阵列上，并提出了一个推动模型来驱动染色体分离[6,7]。该模型包括微管与染色体的端对端取向。或者，染色体被认为沿着微管束聚集[8,9]。从中期开始，第二个模型提出了一种纯粹的侧向染色体与微管的关联，直到后期的最后有丝分裂阶段。在这里，我们应用大规模电子断层扫描[10]对分期的 C. elegans 卵母细胞进行有丝分裂，以分析微管相对于染色体的取向。我们表明，有丝分裂 I 中期的微管主要侧向排列在染色体上，并且在通过后期进展时微管切换到端对端取向。我们进一步表明，这种微管取向的转变涉及一种驱动蛋白-13 微管解聚酶，KLP-7，它去除染色体周围侧向关联的微管。由此，我们得出结论，线虫卵母细胞中微管与染色体的取向的侧向和端对端模式都被相继用于分离有丝分裂染色体。
