Op18 reveals the contribution of nonkinetochore microtubules to the dynamic organization of the vertebrate meiotic spindle
Op18 reveals the contribution of nonkinetochore microtubules to the dynamic organization of the vertebrate meiotic spindle
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DOI：
10.1073/pnas.0902317106
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发表时间：
2009-09-08
影响因子：
11.1
通讯作者：
Kapoor, Tarun M.
中科院分区：
文献类型：
--
作者：
Houghtaling, Benjamin R.;Yang, Ge;Kapoor, Tarun M.
染色体分离的准确性取决于双极纺锤体的组装。有丝分裂纺锤体具有大致相等数量的着丝粒微管 (kMT) 和非着丝粒微管 (非 kMT)，而脊椎动物减数分裂纺锤体主要由非 kMT 组成，其中很大一部分在纺锤体赤道处形成反平行的“桶”阵列。虽然需要 kMT 来驱动染色体分离，但非 kMT 的贡献更为神秘。在这里，我们表明增加 Op18/stathmin（直接控制微管动力学的染色体介导的微管形成途径的一个组成部分）的浓度，可用于消耗非洲爪蟾卵提取物中组装的脊椎动物减数分裂纺锤体中的非 kMT。在这些条件下，kMT 和纺锤杆相关的非 kMT 阵列持续存在于较小的纺锤体中，姐妹动粒之间的距离（着丝粒张力的指标）仍然存在。值得注意的是，驱动蛋白 5（一种保守的运动蛋白，可以推动微管分开，是双极减数分裂纺锤体的组装和维持所必需的）在过量 Op18 存在的情况下不需要维持纺锤体双极性。我们的数据表明，减数分裂纺锤体中的非 kMT 有助于正常的 kMT。我们认为，在没有非 kMT 的情况下，减数分裂中期纺锤体与哺乳动物有丝分裂纺锤体相似，在纺锤体赤道处没有广泛的反平行微管重叠或关键的有丝分裂驱动蛋白的情况下，其平衡力维持中期纺锤体组织。
Accuracy in chromosome segregation depends on the assembly of a bipolar spindle. Unlike mitotic spindles, which have roughly equal amounts of kinetochore microtubules (kMTs) and nonkinetochore microtubules (non-kMTs), vertebrate meiotic spindles are predominantly comprised of non-kMTs, a large subset of which forms an antiparallel "barrel'' array at the spindle equator. Though kMTs are needed to drive chromosome segregation, the contributions of non-kMTs are more mysterious. Here, we show that increasing the concentration of Op18/stathmin, a component of the chromosome-mediated microtubule formation pathway that directly controls microtubule dynamics, can be used to deplete non-kMTs in the vertebrate meiotic spindle assembled in Xenopus egg extracts. Under these conditions, kMTs and the spindle pole-associated non-kMT arrays persist in smaller spindles. In excess Op18, distances between sister kinetochores, an indicator of tension across centromeres, remain unchanged, even though kMTs flux poleward with a approximate to 30% slower velocity, and chromosomes oscillate more than in control metaphase spindles. Remarkably, kinesin-5, a conserved motor protein that can push microtubules apart and is required for the assembly and maintenance of bipolar meiotic spindles, is not needed to maintain spindle bipolarity in the presence of excess Op18. Our data suggest that non-kMTs in meiotic spindles contribute to normal kMT dynamics, stable chromosome positioning, and the establishment of proper spindle size. We propose that without non-kMTs, metaphase meiotic spindles are similar to mammalian mitotic spindles, which balance forces to maintain metaphase spindle organization in the absence of extensive antiparallel microtubule overlap at the spindle equator or a key mitotic kinesin.