Gong Ting, McNally Karen L, Konanoor Siri, Peraza Alma, Bailey Cynthia, Redemann Stefanie, McNally Francis J
Department of Molecular and Cellular Biology, university of California, Davis, Davis, CA 95616, USA.
Department of Cell Biology, University of Virginia, School of Medicine, Charlottesville, VA, USA.
bioRxiv. 2024 Jun 25:2024.04.19.590357. doi: 10.1101/2024.04.19.590357.
In many animal species, the oocyte meiotic spindle, which is required for chromosome segregation, forms without centrosomes. In some systems, Ran-GEF on chromatin initiates spindle assembly. We found that in oocytes, endogenously-tagged Ran-GEF dissociates from chromatin during spindle assembly but re-associates during meiotic anaphase. Meiotic spindle assembly occurred after auxin-induced degradation of Ran-GEF but anaphase I was faster than controls and extrusion of the first polar body frequently failed. In search of a possible alternative pathway for spindle assembly, we found that soluble tubulin concentrates in the nuclear volume during germinal vesicle breakdown. We found that the concentration of soluble tubulin in the metaphase spindle region is enclosed by ER sheets which exclude cytoplasmic organelles including mitochondria and yolk granules. Measurement of the volume occupied by yolk granules and mitochondria indicated that volume exclusion would be sufficient to explain the concentration of tubulin in the spindle volume. We suggest that this concentration of soluble tubulin may be a redundant mechanism promoting spindle assembly near chromosomes.
在许多动物物种中，染色体分离所需的卵母细胞减数分裂纺锤体在没有中心体的情况下形成。在某些系统中，染色质上的Ran-GEF启动纺锤体组装。我们发现，在卵母细胞中，内源性标记的Ran-GEF在纺锤体组装过程中从染色质上解离，但在减数分裂后期重新结合。生长素诱导Ran-GEF降解后发生减数分裂纺锤体组装，但后期I比对照更快，并且第一极体的排出经常失败。为了寻找纺锤体组装的可能替代途径，我们发现可溶性微管蛋白在生发泡破裂期间集中在核体积中。我们发现中期纺锤体区域中可溶性微管蛋白的浓度被内质网片包围，内质网片排除了包括线粒体和卵黄颗粒在内的细胞质细胞器。对卵黄颗粒和线粒体所占体积的测量表明，体积排除足以解释纺锤体体积中微管蛋白的浓度。我们认为，可溶性微管蛋白的这种浓度可能是促进染色体附近纺锤体组装的一种冗余机制。
