In particular, we have followed individual cells through different stages of the cell cycle, instead of monitoring bulk properties of synchronized populations of cells. We have capitalized on newly introduced live-cell imaging approaches to reinvestigate the role of membrane traffic in regulating cell surface area. Interpretation of these findings have emphasized the role of exocytic events during the actomyosin-based constriction responsible for cleavage furrow formation and for abscission (separation of the two daughter cells).
A number of proteins found to be essential for cytokinesis also have established functions in endocytic, exocytic, and recycling pathways. Most recent studies on the role of membrane traffic during cell division have focused on delivery and retrieval of membrane at the cleavage furrow during cytokinesis (for a recent review, see ref. Based on these observations, it was proposed that fusion of these structures with the plasma membrane was responsible for a substantial increase in cell surface area particularly at late stages during mitosis. Imaging along the cell cycle by electron microscopy of neuroblastoma cells showed the appearance of blebs at the plasma membrane and the accumulation of single-bilayer or multilamellar vesicles close to the blebs ( 6). We propose a mechanism by which modulation of endosomal recycling controls cell area and surface expression of membrane-bound proteins during cell division.Īnother way to accommodate the altered surface-to-volume ratio when cells round up is to regulate membrane traffic between the cell surface and its interior, leading to membrane loss at the onset of mitosis and recovery afterward. The total cell-membrane area recovers even in the absence of a functional Golgi apparatus, which would be needed for export of newly synthesized membrane lipids and proteins. Interference with either one of these processes by genetic or chemical means impairs cell division. Clathrin-based endocytosis is normal throughout all phases of cell division, whereas recycling of internalized membranes back to the cell surface slows considerably during the rounding up period and resumes at the time at which recovery of cell membrane begins. How does the total area of plasma membrane change to accommodate these morphological changes and by what mechanism is control of total membrane area achieved? Using single-cell imaging methods, we have found that the amount of plasma membrane in attached cells in culture decreases at the beginning of mitosis and recovers rapidly by the end. Many cells round up during prophase and metaphase and reacquire their extended and flattened shape during cytokinesis. The shape and total surface of a cell and its daughters change during mitosis.
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