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First published online June 14, 2004
doi: 10.1242/10.1242/jcs.01286

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Dynamics and inheritance of the endoplasmic reticulum

¹ Department of Cell Biology
² Howard Hughes Medical Institute, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA

View larger version (55K): [in a new window]   Fig. 1. Models of ER segregation in proliferating animal cells. In interphase (left panel), the peripheral ER forms an interconnected network that is contiguous with the outer membrane of the nuclear envelope. The outer nuclear membrane is biochemically similar to the peripheral ER membrane. By contrast, some integral membrane proteins are localized specifically to the inner nuclear membrane (yellow ovals) or to nuclear pores where the outer and inner nuclear membranes meet (red ovals). In one model of ER segregation (model a), the peripheral ER and the nuclear envelope undergo progressive vesiculation. By metaphase, the cell contains vesicles derived from the peripheral ER or outer nuclear membrane, and from the inner nuclear membrane or nuclear pore domains. Diffusion of these vesicles during metaphase and anaphase ensures the equal partition of ER elements. Another model (model b) predicts that the peripheral ER retains its integrity during mitosis. The nuclear envelope is absorbed into the peripheral ER. The inner nuclear membrane proteins and the nuclear pore integral membrane proteins are distributed throughout the peripheral ER network at early metaphase. Equal segregation of the ER network ensures the faithful partition of components of various ER domains.

View larger version (69K): [in a new window]   Fig. 2. The ER network in the budding yeast S. cerevisiae. Wild-type yeast cells expressing the ER membrane protein Sec63p fused to GFP were visualized by epifluorescence microscopy. The left panel reveals the appearance of cortical ER tubules and the nuclear envelope in the center of a large-budded cell. Cytoplasmic ER tubules that connect cortical ER and the nuclear envelope are readily seen at this focal plane. Focusing on the periphery of the cell (right panel) allows the visualization of the cortical network of interconnected tubules. Figure reproduced with permission from The Rockefeller University Press (Prinz et al., 2000). Both cortical ER and the nuclear envelope remain intact during mitosis.

View larger version (29K): [in a new window]   Fig. 3. A model for cortical ER inheritance in S. cerevisiae. Myo4p transports ER tubules into the daughter cell along actin cables. She3p functions as an adaptor protein that links Myo4p to the segregating ER tubule. Sec3p stabilizes the cortical association of ER tubules delivered into the bud. The ER tubules are propagated along the bud periphery and form an interconnected tubular network.