Department of Physics, Faculty of Science, University of Zagreb, Zagreb, Croatia.
Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia.
Biophys J. 2021 Sep 7;120(17):3641-3648. doi: 10.1016/j.bpj.2021.07.024. Epub 2021 Jul 31.
The highly ordered spatial organization of microtubule bundles in the mitotic spindle is crucial for its proper functioning. The recent discovery of twisted shapes of microtubule bundles and spindle chirality suggests that the bundles extend along curved paths in three dimensions, rather than being confined to a plane. This, in turn, implies that rotational forces, i.e., torques, exist in the spindle in addition to the widely studied linear forces. However, studies of spindle architecture and forces are impeded by a lack of a robust method for the geometric quantification of microtubule bundles in the spindle. In this work, we describe a simple method for measuring and evaluating the shapes of microtubule bundles by characterizing them in terms of their curvature and twist. By using confocal microscopy, we obtain three-dimensional images of spindles, which allows us to trace the entire microtubule bundle. For each traced bundle, we first fit a plane and then fit a circle lying in that plane. With this robust method, we extract the curvature and twist, which represent the geometric information characteristic for each bundle. As the bundle shapes reflect the forces within them, this method is valuable for the understanding of forces that act on chromosomes during mitosis.
微管束在有丝分裂纺锤体中高度有序的空间组织对于其正常功能至关重要。最近发现微管束的扭曲形状和纺锤体的手性表明，束沿着三维弯曲的路径延伸，而不是局限于一个平面。这反过来又意味着，除了广泛研究的线性力之外，纺锤体中还存在旋转力，即扭矩。然而，由于缺乏一种强大的方法来对纺锤体中的微管束进行几何量化，因此对纺锤体结构和力的研究受到了阻碍。在这项工作中，我们描述了一种通过描述其曲率和扭曲来测量和评估微管束形状的简单方法。通过使用共聚焦显微镜，我们获得了纺锤体的三维图像，这使我们能够追踪整个微管束。对于每个追踪的束，我们首先拟合一个平面，然后拟合位于该平面内的一个圆。通过这种强大的方法，我们提取了曲率和扭曲，它们代表了每个束的特征几何信息。由于束的形状反映了其中的力，因此该方法对于理解有丝分裂过程中染色体上的力非常有价值。
