The ESCRT machinery mediates membrane fission in a variety of processes in cells. According to the proposed mechanism, ESCRT-III proteins drive membrane fission by assembling into helical filaments on membranes. Yet, ESCRT-III filaments have never been directly visualized in a process utilizing ESCRTs for its function. Here we used 3D STORM imaging of endogenous ESCRT-III component IST1, to reveal the evolution of the structural organization of ESCRT-III in mammalian cytokinetic abscission. Using this approach, ESCRT-III ring and spiral assemblies were resolved and characterized at different stages of abscission. Visualization of IST1 structures in cells depleted of ESCRT-III components or lacking the microtubule severing enzyme spastin provides further information on the organization and function of the ESCRT-III complex in cells. This work provides the first evidence that ESCRT-III proteins form helical filaments to mediate their function in cells. The new structural information raises new mechanistic scenarios for ESCRT-driven cytokinetic abscission.
