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© The Rockefeller University Press, 0021-9525/1997//1199 $5.00
The Journal of Cell Biology, Volume 137, Number 6, , 1997 1199-1210

Article

Integral Membrane Proteins of the Nuclear Envelope Are Dispersed throughout the Endoplasmic Reticulum during Mitosis



Li Yang, Tinglu Guan, and Larry Gerace

Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037

We have analyzed the fate of several integral membrane proteins of the nuclear envelope during mitosis in cultured mammalian cells to determine whether nuclear membrane proteins are present in a vesicle population distinct from bulk ER membranes after mitotic nuclear envelope disassembly or are dispersed throughout the ER. Using immunofluorescence staining and confocal microscopy, we compared the localization of two inner nuclear membrane proteins (laminaassociated polypeptides 1 and 2 [LAP1 and LAP2]) and a nuclear pore membrane protein (gp210) to the distribution of bulk ER membranes, which was determined with lipid dyes (DiOC6 and R6) and polyclonal antibodies. We found that at the resolution of this technique, the three nuclear envelope markers become completely dispersed throughout ER membranes during mitosis. In agreement with these results, we detected LAP1 in most membranes containing ER markers by immunogold electron microscopy of metaphase cells. Together, these findings indicate that nuclear membranes lose their identity as a subcompartment of the ER during mitosis. We found that nuclear lamins begin to reassemble around chromosomes at the end of mitosis at the same time as LAP1 and LAP2 and propose that reassembly of the nuclear envelope at the end of mitosis involves sorting of integral membrane proteins to chromosome surfaces by binding interactions with lamins and chromatin.

Abbreviations used in this paper: LAP, lamina-associated polypeptide; LBR, lamin binding receptor; NE, nuclear envelope; NPC, nuclear pore complex; NRK, normal rat kidney; GFP, green fluorescent protein.

Address all correspondence to Larry Gerace, Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037. Tel.: (619) 784-8514. Fax: (619) 784-9132.


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