Department of Biosciences and Nutrition, Karolinska Institutet, SE-141 83, Huddinge, Sweden.
Mol Biol Cell. 2022 May 1;33(5):br7. doi: 10.1091/mbc.E21-10-0500. Epub 2022 Mar 2.
During mitosis, sister chromatids congress on both sides of the spindle equator to facilitate the correct partitioning of the genomic material. Chromosome congression requires a finely tuned control of microtubule dynamics by the kinesin motor proteins. In , the kinesin proteins Cin8, Kip1, and Kip3 have a pivotal role in chromosome congression. It has been hypothesized that additional proteins that modulate microtubule dynamics are involved. Here, we show that the microtubule plus-end tracking protein Bik1-the budding yeast ortholog of CLIP-170-is essential for chromosome congression. We find that nuclear Bik1 localizes to the kinetochores in a cell cycle-dependent manner. Disrupting the nuclear pool of Bik1 with a nuclear export signal (Bik1-NES) leads to slower cell-cycle progression characterized by a delayed metaphase-anaphase transition. Bik1-NES cells have mispositioned kinetochores along the spindle in metaphase. Furthermore, using proximity-dependent methods, we identify Cin8 as an interaction partner of Bik1. Deleting CIN8 reduces the amount of Bik1 at the spindle. In contrast, Cin8 retains its typical bilobed distribution in the Bik1-NES mutant and does not localize to the unclustered kinetochores. We propose that Bik1 functions with Cin8 to regulate kinetochore-microtubule dynamics for correct kinetochore positioning and chromosome congression.
在有丝分裂过程中，姐妹染色单体在纺锤体赤道两侧聚集，以促进基因组物质的正确分配。染色体聚集需要驱动蛋白马达蛋白对微管动力学进行精细的调控。在酵母中，驱动蛋白 Cin8、Kip1 和 Kip3 在染色体聚集过程中起着关键作用。人们假设还涉及其他调节微管动力学的蛋白质。在这里，我们表明微管末端追踪蛋白 Bik1——芽殖酵母 CLIP-170 的同源物——对于染色体聚集是必不可少的。我们发现，Bik1 在细胞核中以细胞周期依赖性的方式定位于动粒。用核输出信号（Bik1-NES）破坏 Bik1 的核池会导致细胞周期进程变慢，表现为有丝分裂中期到后期的转变延迟。Bik1-NES 细胞中的动粒在有丝分裂中期沿纺锤体错位。此外，我们使用邻近依赖性方法鉴定出 Cin8 是 Bik1 的相互作用伙伴。删除 CIN8 会减少纺锤体上的 Bik1 含量。相比之下，Cin8 在 Bik1-NES 突变体中保留其典型的双叶分布，并且不会定位到未聚集的动粒上。我们提出，Bik1 与 Cin8 一起作用，调节动粒-微管动力学，以实现正确的动粒定位和染色体聚集。
