Multiple motors cooperate to establish and maintain acentrosomal spindle bipolarity in C. elegans oocyte meiosis.
Multiple motors cooperate to establish and maintain acentrosomal spindle bipolarity in C. elegans oocyte meiosis.
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DOI：
10.7554/elife.72872
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发表时间：
2022-02-11
期刊：
影响因子：
7.7
通讯作者：
Wignall SM
中科院分区：
文献类型：
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作者：
Cavin-Meza G;Kwan MM;Wignall SM
虽然中心体在有丝分裂过程中组织纺锤体极，但在没有中心体的情况下，卵母细胞可以进行减数分裂。人类卵母细胞中的纺锤体经常不能保持双极性，因此发生染色体分离错误，这使得了解促进无着丝体纺锤体稳定的机制变得重要。为此，我们优化了秀丽线虫生长素诱导降解系统，在几分钟内从预先形成的卵母细胞纺锤体中去除这些因素，并评估其对纺锤体结构的影响。这一方法表明，动力蛋白是维持无着丝体极的完整性所必需的；从双极纺锤体中移除动力蛋白会导致极扩张，当与因动力蛋白-12马达KLP-18耗尽而诱导的单极纺锤体结合时，动力蛋白耗尽导致单极完全溶解。令人惊讶的是，我们继续发现，在单极分裂之后，单个染色体能够重组局部微管，并重新建立介导染色体分离的微型双极纺锤体。这表明存在多余的微管分选力，当KLP-18和动力蛋白激活时，这些分选力是无法检测到的。我们发现Kinesin-5家族马达BMK-1提供了这种力量，揭示了Kinesin-5对线虫减数分裂纺锤体组织的贡献。总之，我们的研究揭示了在没有中心体的情况下，多个马达是如何同步工作来建立和维持双极的。减数分裂是一种特殊的细胞分裂形式，产生有性繁殖所需的配子，如卵细胞和精子细胞。在细胞分裂之前，它复制自己的基因组，这样它就有四组染色体。然后，遗传信息在染色体之间洗牌，细胞经历两轮分裂，产生四个在基因上截然不同的配子。在分裂之前，复制的染色体被称为微管的绳状蛋白质聚合物分开。在大多数细胞中，被称为中心体的结构将这些纤维组织成纺锤形，从细胞相反两端的两极发出：然后微管附着到染色体上，并将它们分开。尽管没有中心体，卵细胞或卵母细胞仍然能够将它们的微管排列成类似的两极形状。然而，卵母细胞是如何形成这些无着丝体纺锤体的，人们却知之甚少。中心体并不单独组织纺锤体，并接受动力蛋白等各种马达蛋白的帮助。以前的工作表明，动力蛋白参与了无着丝体极点的排列，但尚不清楚在极最初形成后是否需要将它们保持在一起。为了进行调查，Cavin-Meza等人。开发了一种可以快速从秀丽线虫卵母细胞中去除Dynein的策略。实验表明，在线虫体内，动力蛋白是组装和稳定无着丝体纺锤体所必需的。当动力蛋白和一种额外的运动蛋白KLP-18同时从卵母细胞中移除时，两极都被炸开，完全扰乱了纺锤体的组织。令人惊讶的是，Cavin-Meza等人。发现纺锤体能够改造和分离染色体。进一步的探索首次发现，第三种马达蛋白(称为BMK-1)也有助于将纺锤体组织成双极结构。这些发现揭示了运动蛋白在稳定卵母细胞纺锤体和分离染色体方面发挥的重要作用。减数分裂容易出错，而这些错误是人类流产和出生缺陷的主要原因。因此，了解卵母细胞纺锤体形成和保持稳定的潜在机制，可以解释为什么染色体有时无法分离。这可能最终导致抗击不孕不育的新策略。
While centrosomes organize spindle poles during mitosis, oocyte meiosis can occur in their absence. Spindles in human oocytes frequently fail to maintain bipolarity and consequently undergo chromosome segregation errors, making it important to understand the mechanisms that promote acentrosomal spindle stability. To this end, we have optimized the auxin-inducible degron system in Caenorhabditis elegans to remove the factors from pre-formed oocyte spindles within minutes and assess the effects on spindle structure. This approach revealed that dynein is required to maintain the integrity of acentrosomal poles; removal of dynein from bipolar spindles caused pole splaying, and when coupled with a monopolar spindle induced by depletion of the kinesin-12 motor KLP-18, dynein depletion led to a complete dissolution of the monopole. Surprisingly, we went on to discover that following monopole disruption, individual chromosomes were able to reorganize local microtubules and re-establish a miniature bipolar spindle that mediated chromosome segregation. This revealed the existence of redundant microtubule sorting forces that are undetectable when KLP-18 and dynein are active. We found that the kinesin-5 family motor BMK-1 provides this force, uncovering the first evidence that kinesin-5 contributes to C. elegans meiotic spindle organization. Altogether, our studies have revealed how multiple motors are working synchronously to establish and maintain bipolarity in the absence of centrosomes. Meiosis is a specialized form of cell division that produces the gametes required for sexual reproduction, such as egg and sperm cells. Before the cell splits, it copies its genome so that it has four sets of chromosomes. Genetic information is then shuffled between the chromosomes, and the cell undergoes two rounds of division, resulting in four gametes that are genetically distinct. Prior to division, the duplicated chromosomes are separated by rope-like protein polymers called microtubules. In most cells, structures called centrosomes organize these fibers into a spindle shape that emanates from two ‘poles’ on opposite ends of the cell: the microtubules then attach to the chromosomes and pull them apart. Despite not having centrosomes, egg cells, or ‘oocytes’, are still able to arrange their microtubules into a similar bipolar shape. However, how oocytes form these ‘acentrosomal’ spindles is poorly understood. Centrosomes do not organize the spindle alone, and receive help from various motor proteins such as dynein. Previous work showed that dynein is involved in arranging acentrosomal poles, but it was not known if it was required to hold the poles together after they initially formed. To investigate, Cavin-Meza et al. developed a strategy that can rapidly remove dynein from oocytes of the roundworm Caenorhabditis elegans. The experiment showed that dynein is required both to assemble and stabilize acentrosomal spindles in C. elegans. When dynein and an additional motor protein, KLP-18, were both removed from oocytes simultaneously, the poles blew apart, completely disrupting spindle organization. Surprisingly, Cavin-Meza et al. found that the spindles were able to reform and separate the chromosomes. Further probing revealed, for the first time, that a third motor protein (called BMK-1) also helps to organize the spindle into its bipolar structure. These findings reveal the important role motor proteins play in stabilizing spindles and separating chromosomes in oocytes. Meiosis is prone to mistakes, and these errors are a major cause of miscarriages and birth defects in humans. Therefore, understanding the underlying mechanisms of how oocyte spindles form and remain stable could shed light on why chromosomes sometimes fail to segregate. This may eventually lead to new strategies for combating infertility.