Department of Genetics, University of Cambridge, Downing Street, Cambridge CB2 3EH, UK.
Curr Biol. 2012 Jun 19;22(12):1075-83. doi: 10.1016/j.cub.2012.04.059. Epub 2012 May 17.
Budding yeast is a unique model to dissect spindle orientation in a cell dividing asymmetrically. In yeast, this process begins with the capture of pole-derived astral microtubules (MTs) by the polarity determinant Bud6p at the cortex of the bud in G(1). Bud6p couples MT growth and shrinkage with spindle pole movement relative to the contact site. This activity resides in N-terminal sequences away from a domain linked to actin organization. Kip3p (kinesin-8), a MT depolymerase, may be implicated, but other molecular details are essentially unknown.
We show that Bud6p and Kip3p play antagonistic roles in controlling the length of MTs contacting the bud. The stabilizing role of Bud6p required the plus-end-tracking protein Bim1p (yeast EB1). Bim1p bound Bud6p N terminus, an interaction that proved essential for cortical capture of MTs in vivo. Moreover, Bud6p influenced Kip3p dynamic distribution through its effect on MT stability during cortical contacts via Bim1p. Coupling between Kip3p-driven depolymerization and shrinkage at the cell cortex required Bud6p, Bim1p, and dynein, a minus-end-directed motor helping tether the receding plus ends to the cell cortex. Validating these findings, live imaging of the interplay between dynein and Kip3p demonstrated that both motors decorated single astral MTs with dynein persisting at the plus end in association with the site of cortical contact during shrinkage at the cell cortex.
Astral MT shrinkage linked to Bud6p involves its direct interaction with Bim1p and the concerted action of two MT motors-Kip3p and dynein.
出芽酵母是解析不对称分裂细胞中纺锤体取向的独特模型。在酵母中，这个过程始于极性决定因子 Bud6p 在 G1 期在芽的皮质处捕获来自极的星体微管（MT）。Bud6p 将 MT 生长和收缩与相对于接触点的纺锤极运动偶联。这种活性位于远离与肌动蛋白组织相关联的结构域的 N 端序列中。可能涉及解聚酶 Kip3p（驱动蛋白-8），但其他分子细节基本上未知。
我们表明 Bud6p 和 Kip3p 在控制接触芽的 MT 长度方面发挥拮抗作用。Bud6p 的稳定作用需要末端追踪蛋白 Bim1p（酵母 EB1）。Bim1p 结合 Bud6p N 端，该相互作用对于体内 MT 在皮质处的捕获是必不可少的。此外，Bud6p 通过其在皮质接触过程中对 MT 稳定性的影响影响 Kip3p 的动态分布。通过 Bud6p 影响 MT 稳定性，Kip3p 驱动的解聚和细胞皮层收缩之间的偶联需要 Bud6p、Bim1p 和动力蛋白，后者是一种帮助将缩回的正极系绳固定到细胞皮层的负向导向马达。通过活细胞成像验证了这些发现，该成像显示了动力蛋白和 Kip3p 之间相互作用，这两个马达都用动力蛋白修饰单个星体 MT，在细胞皮层收缩期间，动力蛋白在与皮质接触部位相关联的正极保留。
与 Bud6p 相关的星体 MT 收缩涉及它与 Bim1p 的直接相互作用以及两种 MT 马达-Kip3p 和动力蛋白的协同作用。
