Coupling changes in cell shape to chromosome segregation

Key Points Animal cells undergo dramatic changes in their shape as they progress through mitosis and division. This process begins with rounding soon after cells enter mitosis. Mitotic rounding is an active process that depends on a combination of de-adhesion, actomyosin-based contraction and osmotic swelling. Adhesion remodelling is essential for normal cell rounding during mitosis and is triggered by inactivation of the small GTPase RAP1. Entry into mitosis triggers a dramatic change in actin organization and dynamics, leading to the assembly of a formin-based actomyosin network that is tethered to the overlying membrane by activated ERM (Ezrin, Radixin, Moesin) proteins. The changes in actin organization and cell shape that accompany mitotic exit are driven by a combination of actomyosin ring assembly and polar relaxation, which can be induced by chromatin-based signals. Whereas remodelling of the actin and microtubule cytoskeletons seems to be relatively independent during mitotic entry, spindle elongation and cytokinesis must be tightly coupled in space and time to ensure precise cell division. When animal cells divide, they undergo dramatic changes in shape, polarity and mechanical properties. At mitotic entry, the remodelling of cortical actomyosin and cell–substrate adhesions, combined with osmotic swelling enable cell rounding, which is then reversed as cells exit mitosis. We now have a better understanding of the regulation of such shape changes and how they contribute to accurate segregation of chromosomes and other cellular components. Animal cells undergo dramatic changes in shape, mechanics and polarity as they progress through the different stages of cell division. These changes begin at mitotic entry, with cell–substrate adhesion remodelling, assembly of a cortical actomyosin network and osmotic swelling, which together enable cells to adopt a near spherical form even when growing in a crowded tissue environment. These shape changes, which probably aid spindle assembly and positioning, are then reversed at mitotic exit to restore the interphase cell morphology. Here, we discuss the dynamics, regulation and function of these processes, and how cell shape changes and sister chromatid segregation are coupled to ensure that the daughter cells generated through division receive their fair inheritance.