12002:

Dynamic Changes in 3-Dimensional Distribution of Golgi Stacks During Mitosis and Cytokinesis.

Authors:	Nebenführ, Andreas(A)Frohlick, Jennifer, A.(A)Staehelin, L. Andrew(A)
Affiliations:	(A): University of Colorado, MCD Biology
Presenter:	Nebenführ, Andreas , andreas.nebenfuehr@colorado.edu

Cell division in angiosperms differs dramatically from the corresponding processes in other eukaryotes. The first visible difference is the formation of a cortical band of microtubules (MTs) and microfilaments (MFs). This preprophaseband (PPB) ultimately determines the site of cell division, but degenerates at the onset of mitosis. At the end of mitosis, the phragmoplast is initiated at the center between the two daughter nuclei. The phragmoplast is a complex assembly of MTs, MFs, and ER membranes that is thought to be necessary to guide Golgi products to the site of cell plate formation. As the phragmoplast expands to form a ring-like structure at the leading edge of the cell plate the cell plate also grows outward to the location of the former PPB. Assembly of the cell plate itself requires the delivery and fusion of Golgi-derived vesicles that carry cell wall components as well as biosynthetic enzymes, such as callose and cellulose synthase. The secretory apparatus of plant cells therefore must be continuously active during cytokinesis. This high level of dependence on Golgi products raises the question whether the highly ordered structure of the cytokinetic apparatus is accompanied by an ordered spatial arrangement of Golgi stacks in the vicinity of the phragmoplast. We have investigated this question by studying the Golgi stack distribution in dividing tobacco BY-2 suspension culture cells. The stacks in these cells were labeled with green fluorescent protein (GFP) fused to a resident Golgi protein, a-1,2 mannosidase from soybean, allowing for observation of dynamic changes in living cells. Before the onset of mitosis, the majority of stacks accumulate in a perinuclear region, the phragmosome, which at this time contains most of the cytoplasm in the cell. During mitosis, the stacks within the phragmosome region are generally excluded from the spindle and chromosome regions, but retain an otherwise random localization. In late telophase, a few Golgi stacks appear between the forming daughter nuclei, but are excluded from the phragmoplast. As the phragmoplast is displaced centrifugally, Golgi stacks approach the more mature region of the cell plate in the center of the cell. Thus, our observations suggest a spatially close association of the majority of Golgi stacks with the cytokinetic apparatus while at the same time they are being excluded from regions of high cytoskeletal density. Supported by NIH grant GM18639 to LAS.