Abstract

During cell division, the duplicated chromosomes are physically separated by the action of the mitotic spindle. The mitotic spindle is a dynamic structure of the cytoskeleton, which consists of two microtubule asters. Its orientation defines the axis along which the cell divides. Recent experiments on dividing cells, which adhere to patterned substrates, show that the spindle orientation depends on the spatial distribution of cell adhesion sites. In this talk I will show that the experimentally observed spindle orientation can be understood as the result of the action of cortical force generators acting on the spindle microtubules. We develop a simple physical description of the spindle mechanics based on the assumption that the local activity of force generators is controlled by the spatial distribution of cell adhesion sites. We calculate the torque acting on the spindle, as well as the energy profile and the angular distribution of spindle orientation. Our model accounts for the preferred spindle orientation, as well as the full shape of the angular distributions of spindle orientation observed in a wide variety of pattern geometries.