Cell division culminates in cytokinesis, the step that separates the two daughter cells after successful completion of the previous cell cycle phases. The physical separation by severing the bridge that connects the cells, termed abscission, involves the endosomal sorting complex required for transport-III (ESCRT-III). Piel and colleagues now report that ESCRT-III assembly and abscission are triggered by releasing the tension that the daughter cells exert on the intercellular bridge (Science 339, 1625–1629; 2013).

The authors seeded cells on different sizes of disc-shaped fibronectin micropatterns and observed that abscission was delayed when cells were subjected to a low degree of spatial confinement and were able to move apart from each other. Surprisingly, the longer abscission time was the result of increased pulling forces on the bridge, which in turn depended on ROCK-regulated cell contractility and high membrane tension. The authors performed a series of laser ablation experiments combined with RNAi-mediated depletion of known regulators of abscission, including the CHMP4B ESCRT-III component. These results showed that reducing tension by laser-mediated cutting of the bridge on one side induced the late-stage assembly of the ESCRT-III complex and subsequent abscission of the remaining part of the bridge. Although the mechanism by which tension release promotes ESCRT-III complex formation remains to be elucidated, these findings add to our understanding of how the timing of cytokinetic abscission is regulated.