Baumgärtner Stephan, Tolić Iva M
Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany.
Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany; Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia.
PLoS One. 2014 Apr 10;9(4):e93781. doi: 10.1371/journal.pone.0093781. eCollection 2014.
Positioning of the mitotic spindle is crucial for proper cell division. In the budding yeast Saccharomyces cerevisiae, two mechanisms contribute to spindle positioning. In the Kar9 pathway, astral microtubules emanating from the daughter-bound spindle pole body interact via the linker protein Kar9 with the myosin Myo2, which moves the microtubule along the actin cables towards the neck. In the dynein pathway, astral microtubules off-load dynein onto the cortical anchor protein Num1, which is followed by dynein pulling on the spindle. Yet, the mechanism by which microtubules target cortical anchor sites is unknown. Here we quantify the pivoting motion of astral microtubules around the spindle pole bodies, which occurs during spindle translocation towards the neck and through the neck. We show that this pivoting is largely driven by the Kar9 pathway. The microtubules emanating from the daughter-bound spindle pole body pivot faster than those at the mother-bound spindle pole body. The Kar9 pathway reduces the time needed for an astral microtubule inside the daughter cell to start pulling on the spindle. Thus, we propose a new role for microtubule pivoting: By pivoting around the spindle pole body, microtubules explore the space laterally, which helps them search for cortical anchor sites in the context of spindle positioning in budding yeast.
有丝分裂纺锤体的定位对于细胞的正常分裂至关重要。在出芽酵母酿酒酵母中，有两种机制有助于纺锤体定位。在Kar9途径中，从与子细胞相连的纺锤体极体发出的星状微管通过连接蛋白Kar9与肌球蛋白Myo2相互作用，Myo2沿着肌动蛋白电缆将微管移向颈部。在动力蛋白途径中，星状微管将动力蛋白卸载到皮质锚定蛋白Num1上，随后动力蛋白拉动纺锤体。然而，微管靶向皮质锚定位点的机制尚不清楚。在这里，我们量化了星状微管围绕纺锤体极体的枢转运动，这种运动发生在纺锤体向颈部移动并穿过颈部的过程中。我们表明，这种枢转很大程度上是由Kar9途径驱动的。从与子细胞相连的纺锤体极体发出的微管比与母细胞相连的纺锤体极体处的微管枢转得更快。Kar9途径减少了子细胞内的星状微管开始拉动纺锤体所需的时间。因此，我们提出了微管枢转的一个新作用：通过围绕纺锤体极体枢转，微管在横向探索空间，这有助于它们在出芽酵母纺锤体定位的背景下寻找皮质锚定位点。
