Institute of Molecular Biology and Department of Biology, 1229 University of Oregon, Eugene, Oregon 97403, USA.
Institute of Molecular Biology and Department of Biology, 1229 University of Oregon, Eugene, Oregon 97403, USA
Biol Open. 2020 Jun 25;9(6):bio052308. doi: 10.1242/bio.052308.
How oocytes assemble bipolar meiotic spindles in the absence of centrosomes as microtubule organizing centers remains poorly understood. We have used live cell imaging in to investigate requirements for the nuclear lamina and for conserved regulators of microtubule dynamics during oocyte meiosis I spindle assembly, assessing these requirements with respect to recently identified spindle assembly steps. We show that the nuclear lamina is required for microtubule bundles to form a peripheral cage-like structure that appears shortly after oocyte nuclear envelope breakdown and surrounds the oocyte chromosomes, although bipolar spindles still assembled in its absence. Although two conserved regulators of microtubule nucleation, RAN-1 and γ-tubulin, are not required for bipolar spindle assembly, both contribute to normal levels of spindle-associated microtubules and spindle assembly dynamics. Finally, the XMAP215 ortholog ZYG-9 and the nearly identical minus-end directed kinesins KLP-15/16 are required for proper assembly of the early cage-like structure of microtubule bundles, and for early spindle pole foci to coalesce into a bipolar structure. Our results provide a framework for assigning molecular mechanisms to recently described steps in oocyte meiosis I spindle assembly.
卵母细胞在缺乏微管组织中心的情况下如何组装两极有丝分裂纺锤体，目前还知之甚少。我们在 中使用活细胞成像来研究核纤层在卵母细胞第一次减数分裂纺锤体组装过程中的作用，以及保守的微管动力学调控因子的作用，同时评估这些作用与最近发现的纺锤体组装步骤的关系。我们发现，核纤层对于微管束形成一个外周笼状结构是必需的，该结构在卵母细胞核膜破裂后不久出现，并环绕卵母细胞染色体，尽管在没有核纤层的情况下仍能组装两极纺锤体。虽然两个保守的微管起始调控因子 RAN-1 和 γ-微管蛋白对于两极纺锤体的组装不是必需的，但它们都有助于正常水平的纺锤体相关微管和纺锤体组装动力学。最后，ZYG-9 同源物 XMAP215 和几乎相同的微管负端定向驱动蛋白 KLP-15/16 对于微管束早期笼状结构的正确组装，以及早期纺锤体极焦点融合成两极结构是必需的。我们的研究结果为将分子机制分配到最近描述的卵母细胞第一次减数分裂纺锤体组装步骤提供了一个框架。
