Segal M, Bloom K, Reed S I
Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Mol Biol Cell. 2000 Nov;11(11):3689-702. doi: 10.1091/mbc.11.11.3689.
In budding yeast, spindle polarity relies on a precise temporal program of cytoplasmic microtubule-cortex interactions throughout spindle assembly. Loss of Clb5-dependent kinase activity under conditions of attenuated Cdc28 function disrupts this program, resulting in diploid-specific lethality. Here we show that polarity loss is tolerated by haploids due to a more prominent contribution of microtubule-neck interactions to spindle orientation inherent to haploids. These differences are mediated by the relative partition of Bud6 between the bud tip and bud neck, distinguishing haploids from diploids. Bud6 localizes initially to the bud tip and accumulates at the neck concomitant with spindle assembly. bud6Delta mutant phenotypes are consistent with Bud6's role as a cortical cue for cytoplasmic microtubule capture. Moreover, mutations that affect Bud6 localization and partitioning disrupt the sequential program of microtubule-cortex interactions accordingly. These data support a model whereby Bud6 sequentially cues microtubule capture events at the bud tip followed by capture events at the bud neck, necessary for correct spindle morphogenesis and polarity.
在出芽酵母中，纺锤体极性依赖于整个纺锤体组装过程中细胞质微管与皮层相互作用的精确时间程序。在Cdc28功能减弱的条件下，Clb5依赖性激酶活性的丧失会破坏这一程序，导致二倍体特异性致死。在这里，我们表明单倍体能够耐受极性丧失，这是因为微管-颈部相互作用对单倍体固有的纺锤体定向贡献更为显著。这些差异是由Bud6在芽尖和芽颈之间的相对分配介导的，从而区分了单倍体和二倍体。Bud6最初定位于芽尖，并随着纺锤体组装在颈部积累。bud6Delta突变体表型与Bud6作为细胞质微管捕获的皮层信号的作用一致。此外，影响Bud6定位和分配的突变相应地破坏了微管-皮层相互作用的顺序程序。这些数据支持了一个模型，即Bud6依次引导芽尖的微管捕获事件，随后是芽颈的捕获事件，这对于正确的纺锤体形态发生和极性是必要的。
