Abstract
Mammalian cytokinesis proceeds by constriction of an actomyosin ring and furrow ingression, resulting in the formation of the midbody bridge connecting two daughter cells. At the centre of the midbody resides the Flemming body, a dense proteinaceous ring surrounding the interlocking ends of anti-parallel microtubule arrays. Abscission, the terminal step of cytokinesis, occurs near the Flemming body. A series of broad processes govern abscission: the initiation and stabilisation of the abscission zone, followed by microtubule severing and membrane scission—The latter mediated by the endosomal sorting complex required for transport (ESCRT) proteins. A key goal of cell and developmental biologists is to develop a clear understanding of the mechanisms that underpin abscission, and how the spatiotemporal coordination of these events with previous stages in cell division is accomplished. This article will focus on the function and dynamics of the ESCRT proteins in abscission and will review recent work, which has begun to explore how these complex protein assemblies are regulated by the cell cycle machinery.
Highlights
Mammalian cytokinesis proceeds by constriction of an actomyosin ring and furrow ingression, resulting in the formation of the midbody bridge connecting two daughter cells
The final step, cleavage of the membrane bridge, is mediated by the endosomal sorting complex required for transport (ESCRT) proteins, which are known to mediate a diverse array of membrane remodelling activities [3]
A further model was proposed by Saksena and colleagues who proposed that ESCRT-III binds directly to the ESCRT-II complex and oligomerises directly on the membrane into a filament; This led these workers to suggest that ESCRT-III forms a ring that is disassembled by the action of VPS4 at one end, with the net effect resembling a purse-string construction [21]
Summary
The newly formed daughter cells remain attached by a thin intercellular bridge; Abscission completes the formation of the daughter cells by cleaving this bridge (Figure 1) [1,2]. A further model was proposed by Saksena and colleagues who proposed that ESCRT-III binds directly to the ESCRT-II complex and oligomerises directly on the membrane into a filament; This led these workers to suggest that ESCRT-III forms a ring that is disassembled by the action of VPS4 at one end, with the net effect resembling a purse-string construction [21] These different models all agree that ESCRT-III is intimately linked to scission, and that VPS4 is required both to redistribute ESCRT-III subunits back into the cytoplasm and has been shown to be necessary for all ESCRT-mediated processes [22,23]. Regardless of mechanism, the overwhelming body of recent evidence has placed ESCRT and ESCRT-associated proteins, such as VPS4, at the heart of the abscission mechanism together with a growing list of ESCRT-associated proteins that appear to play important roles in regulating aspects of ESCRT function, including cytokinesis (see for example [26,27,28])
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