IMC16, Sapporo, 2006
Partitioning of the Endoplasmic Reticulum during Cell Division
Maija Rantanen1*, Helena Vihinen1 and Eija Jokitalo1
1
Institute of Biotechnology, Electron Microscopy Unit, University of Helsinki, Finland
*Correspondence: [email protected]
Partitioning of the major subdomains of the endoplasmic reticulum (ER) - the nuclear envelope (NE), rough and smooth
ER - in animal cells during cell division is poorly understood. Electron microscopic data suggests partial fragmentation of the
membranes in some cell types [1]. On the other hand, light microscopy shows that after NE breakdown (NEBD) some of NE
components disperse into peripheral ER which remains continuous throughout the cell division [2]. It is not known, however,
whether NE proteins spread evenly throughout ER, and whether ER network organization itself changes during cell division.
Morphology of NE and peripheral ER of interphase and mitotic Chinese hamster ovary cells were studied with light and
electron microscope. Live cells carrying either NE or total ER labels were imaged in three dimensions with confocal
microscope and similarly labeled fixed cells observed with electron microscope. Three-way-junctions reflecting the degree of
ER networking and tubule lengths of ER profiles in confocal optical sections (FIG. 1) and electron micrographs (FIG. 2)
were quantified.
In confocal images, ER of the dividing cells appeared tightly networked. The labelling pattern of the NE protein lamin B
receptor resembled that of total ER labelling after NEBD to the end of anaphase. After that it accumulated on NE
surrounding the chromosomes. Electron micrographs and 3D tomography of mitotic cells confirmed continuity of the ER
network and dispersion of NE label into ER. However, a more careful inspection revealed many unstained tubules next to and
continuous with stained ones. Quantification of ER profiles from both confocal and EM images showed more three-wayjunctions and short tubules than in interphase cells. These observations suggest the ER organization of the dividing cells is
different from that of interphase cells, which may be required to ensure even distribution of ER to both daughter cells.
[1] Warren G. and Wickner W., Cell, 84 (1996), 395-400
[2] Ellenberg J., Siggia E.D., Moreira J.E., Smith C.L., Presley J.F., Worman H.J., Lippincott-Schwartz J., J Cell Biol, 138
(1997),1193-1206
[3] We want to thank Academy of Finland and Viikki Graduate School in Biosciences for financial support.
A
B
C
FIG. 1. Image stacks of live mitotic and interphase cells were obtained with confocal microscope (a)
and deconvoluted (b) for image analysis. Skeletonized images (c) were used to quantify 3-way-junctions
and ER tubule lengths. Bar, 5 µm.
FIG. 2. Thin section EM image of a prophase cell with cytochemical staining of the total ER. Close up shows
ER tubules, three-way junctions (arrow heads) and ER exit sites (stars) that are also stained. Bars, 1 µm.
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