Wilson P G, Fuller M T, Borisy G G
Laboratory of Molecular Biology, University of Wisconsin, Madison 53706, USA.
J Cell Sci. 1997 Feb;110 ( Pt 4):451-64. doi: 10.1242/jcs.110.4.451.
Implicit to all models for mitotic spindle assembly is the view that centrosomes are essentially permanent structures. Yet, immunofluorescence revealed that spindles in larval brains of urchin mutants in Drosophila were frequently monastral but bipolar; the astral pole contained a centrosome while the opposing anastral pole showed neither gamma tubulin nor a radial array of astral microtubules. Thus, mutations in the urchin gene seem to uncouple centrosome organization and spindle bipolarity in mitotic cells. Hypomorphic mutants showed a high frequency of monastral bipolar spindles but low frequencies of polyploidy, suggesting that monastral bipolar spindles might be functional. To test this hypothesis, we performed pedigree analysis of centrosome distribution and spindle structure in the four mitotic divisions of gonial cells. Prophase gonial cells showed two centrosomes, suggesting cells entered mitosis with the normal number of centrosomes and that centrosomes separated during prophase. Despite a high frequency of monastral bipolar spindles, the end products of the four mitotic divisions were equivalent in size and chromatin content. These results indicate that monastral bipolar spindles are functional and that the daughter cell derived from the anastral pole can assemble a functional bipolar spindle in the subsequent cell cycle. Cell proliferation despite high frequencies of monastral bipolar spindles can be explained if centrosome structure in mitotic cells is dynamic, allowing transient and benign disorganization of pericentriolar components. Since urchin proved to be allelic to KLP61F which encodes a kinesin related motor protein (Heck et al. (1993) J. Cell Biol. 123, 665-671), our results suggest that motors influence the dynamic organization of centrosomes.
所有有丝分裂纺锤体组装模型都隐含着这样一种观点，即中心体本质上是永久性结构。然而，免疫荧光显示，果蝇海胆突变体幼虫大脑中的纺锤体常常是单星体但具有双极；星体极含有一个中心体，而相对的无星体极既没有γ微管蛋白，也没有星体微管的放射状排列。因此，海胆基因的突变似乎在有丝分裂细胞中使中心体组织和纺锤体双极性解偶联。亚效突变体显示单星体双极纺锤体的频率很高，但多倍体的频率很低，这表明单星体双极纺锤体可能是有功能的。为了验证这一假设，我们对生殖细胞的四个有丝分裂过程中的中心体分布和纺锤体结构进行了谱系分析。前期生殖细胞显示有两个中心体，这表明细胞进入有丝分裂时中心体数量正常，且中心体在前期分离。尽管单星体双极纺锤体的频率很高，但四个有丝分裂过程的最终产物在大小和染色质含量上是相等的。这些结果表明，单星体双极纺锤体是有功能的，并且来自无星体极的子细胞可以在随后的细胞周期中组装一个有功能的双极纺锤体。如果有丝分裂细胞中的中心体结构是动态的，允许中心粒周围成分出现短暂且良性的紊乱，那么即使单星体双极纺锤体频率很高，细胞增殖也可以得到解释。由于已证明海胆与编码驱动蛋白相关运动蛋白的KLP61F是等位基因（赫克等人（1993年）《细胞生物学杂志》123卷，665 - 671页），我们的结果表明运动蛋白影响中心体的动态组织。
