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* Cell Biology Laboratory, Imperial Cancer Research Fund, London WC2A, 3PX, UK; The Golgi apparatus of HeLa cells was fluorescently tagged with a green fluorescent protein
(GFP), localized by attachment to the NH2-terminal retention signal of N-acetylglucosaminyltransferase I
(NAGT I). The location was confirmed by immunogold
and immunofluorescence microscopy using a variety of
Golgi markers. The behavior of the fluorescent Golgi
marker was observed in fixed and living mitotic cells using confocal microscopy. By metaphase, cells contained a constant number of Golgi fragments dispersed
throughout the cytoplasm. Conventional and cryoimmunoelectron microscopy showed that the NAGT
I-GFP chimera (NAGFP)-positive fragments were tubulo-vesicular mitotic Golgi clusters. Mitotic conversion of Golgi stacks into mitotic clusters had surprisingly little effect on the polarity of Golgi membrane
markers at the level of fluorescence microscopy. In living cells, there was little self-directed movement of the clusters in the period from metaphase to early telophase. In late telophase, the Golgi ribbon began to be
reformed by a dynamic process of congregation and tubulation of the newly inherited Golgi fragments. The
accuracy of partitioning the NAGFP-tagged Golgi was
found to exceed that expected for a stochastic partitioning process. The results provide direct evidence for mitotic clusters as the unit of partitioning and suggest that
precise regulation of the number, position, and compartmentation of mitotic membranes is a critical feature for the ordered inheritance of the Golgi apparatus.
Department of Microbiology and
Immunology, Stanford University School of Medicine, Stanford, California 94305-5402; and § Departement de Biologie
Cellulaire, Universite de Geneve, CH-1211 Geneve 4, Switzerland
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