Mechanisms of the disassembly and reassembly of organelles during mitosis

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At the onset of mitosis vesicle-mediated protein transport is inhibited, and organelles such as the Golgi and nuclear envelope are disassembled into small vesicles. At telophase the small vesicles are fused each other to form intact organelles. Although recent studies revealed that NSF and VCP are involved in the fusion of Golgi-derived vesicles, the mechanisms of the assembly and disassembly of organelles have not been fully understood. In the present study we studied the mechanism of the biogenesis of organelles including the nuclear envelope, Golgi apparatus, and endoplasmic reticulum. The followings are the results obtained.1. NSF is associated with the membrane-embedded SNARE complex via SNAP.NSF is localized not only at the Golgi apparatus but also at the nuclear envelope. An antibody against a subunit of the SNARE complex, SNAP-25, inhibits the fusion of nuclear membrane vesicles in vitro, suggesting the involvement of the NSF-SNAP-SNARE complex in the nuclear membrane fusion.2. The Golgi apparatus is disassembled by nordihydroguaiaretic acid in a mechanism dependent on trimeric GTP-binding proteins. This disassembly was suppressed by overexpression of alpha_<12> or alpha_2, but not other species, suggesting the involvement of specific alpha subunits in the organization of this organelle.3. A novel syntaxin species (syntaxin 18) was identified. Syntaxin 18 is most likely a homologue of yeast Ufe1p, a protein involved in the fusion of nuclear or endoplasmic reticulum membranes. The role of syntaxin 18 in the organization of the endoplasmic reticulum is under investigation.