Redundant microtubule abscission mechanisms buffer mechanical heterogeneities

In the final step of cell division, cytokinesis, the cytoplasm is partitioned in two, forming a cytoplasmic bridge between the daughter cells. Typically, cytokinesis is followed by abscission, the physical severing of the bridge. The severing of the membrane during abscission is mediated by the ESCRT-III machinery, which also recruits microtubule severing proteins to remove the microtubules of the bridge. Pulling forces on the bridge have been proposed to act as regulators of abscission by influencing the localization of the ESCRT-III complex. However, how forces are integrated by cells during abscission in a developmental context remains elusive. Here, we use pluripotent stem cells, where abscission is slow keeping the two daughter cells connected for hours, to show that the cytoskeleton buffers mechanical heterogeneities to ensure abscission. We show that cells can cut their microtubules in two distinct ways. Slow abscission is associated with an asymmetric cut in the microtubule lattice, while during fast abscission, the microtubules are gradually removed on both sides of the bridge. We show that the contractility of the actin cortex mediates this choice between the two abscission modes through modulation of the master kinase Aurora B. Finally, the choice between the abscission mode depends on and impacts fate choice dynamics.