Cytokinetic abscission, the terminal step of cell division, crucially depends on the local constriction of ESCRT-III helices after cytoskeleton disassembly. While the microtubules of the intercellular bridge are cut by the ESCRT-associated enzyme Spastin, the mechanism that clears F-actin at the abscission site is unknown. Here we show that oxidation-mediated depolymerization of actin by the redox enzyme MICAL1 is key for ESCRT-III recruitment and successful abscission. MICAL1 is recruited to the abscission site by the Rab35 GTPase through a direct interaction with a flat three-helix domain found in MICAL1 C terminus. Mechanistically, in vitro assays on single actin filaments demonstrate that MICAL1 is activated by Rab35. Moreover, in our experimental conditions, MICAL1 does not act as a severing enzyme, as initially thought, but instead induces F-actin depolymerization from both ends. Our work reveals an unexpected role for oxidoreduction in triggering local actin depolymerization to control a fundamental step of cell division.

Cytokinesis requires the constriction of ESCRT-III filaments on the side of the midbody, where abscission occurs. After ESCRT recruitment at the midbody, it is not known how the ESCRT-III machinery localizes to the abscission site. To reveal actors involved in abscission, we obtained the proteome of intact, post-abscission midbodies (Flemmingsome) and identified 489 proteins enriched in this organelle. Among these proteins, we further characterized a plasma membrane-to-ESCRT module composed of the transmembrane proteoglycan syndecan-4, ALIX and syntenin, a protein that bridges ESCRT-III/ALIX to syndecans. The three proteins are highly recruited first at the midbody then at the abscission site, and their depletion delays abscission. Mechanistically, direct interactions between ALIX, syntenin and syndecan-4 are essential for proper enrichment of the ESCRT-III machinery at the abscission site, but not at the midbody. We propose that the ESCRT-III machinery must be physically coupled to a membrane protein at the cytokinetic abscission site for efficient scission, uncovering common requirements in cytokinesis, exosome formation and HIV budding.

Cells don't simply separate at cytokinesis. While furrow contraction critically relies on myosin-II and F-actin, post-furrowing steps are less understood but involve the constriction of ESCRT-III polymer-dependent helices on the side of the midbody, which likely drive final abscission. The first evidence that animal cell cytokinesis requires membrane traffic, as in plant cells, was provided about 15 years ago. Since then, it has become increasingly clear that fusion of vesicles to the cytokinetic furrow is essential in large embryonic cells, and that membrane traffic within the intercellular bridge is crucial for its stability and successful abscission in all animal cells. Here, we review our current knowledge of the secretory and endocytic recycling pathways involved in cytokinesis, and how vesicles defined by specific Rab and Arf GTPases are targeted and fused to the membrane of the intercellular bridge thanks to different molecular motors, tethering complexes and SNARE machineries. At the functional level, we will describe how membrane traffic can remodel both phosphoinositide lipids and promote F-actin clearance necessary for ESCRT-III-dependent abscission, and identify key unanswered questions in the field. We will finally review recent evidence showing a tight coupling between membrane traffic and cytokinesis in complex processes, such as during the establishment of de novo apico-basal polarity.