Highly dynamic and interdependent organization of distinct subcellular structures. The Vero cells in (a) show the normal arrangement of microtubules (green) radiating from the microtubule-organizing center. The Golgi complex (indicated by the arrow), a membrane-bounded organelle through which all secretory proteins pass en route to the cell surface, is stained with antibodies against the coat protein complex COPI (red; where red and green staining coincide they appear yellow). The Golgi complex resides as a tight structure at a central perinuclear location. The cell in (b) has been treated with the drug brefeldin A, which causes rapid removal of the COPI coat from Golgi membranes into a cytoplasmic pool, followed by disassembly of the Golgi apparatus. The microtubule network remains unaffected by this treatment, however. (c) Treatment of a cell with the drug nocodazole causes disassembly of the microtubules into their respective cytoplasmic tubulin monomers. This breakdown of the microtubule network, a key component of cell architecture, also results in the breakdown of the Golgi complex into distinct fragments spread throughout the cell (as indicated by the arrowheads). The cell in (d) has been transfected with a GFP-tagged novel cDNA, which when expressed localizes along the entire microtubule network (green). But as the expression level of this protein increases, it interferes with the microtubule network with the concomitant result that the Golgi is fragmented in a similar manner to that observed in (c) (as indicated by the arrowheads). This phenotypic effect illustrates the dynamic interdependency of organelles exemplified by Golgi morphology and the microtubule network. The nuclei of all the cells have also been stained with the DNA-chelating agent diamino phenylindole (DAPI; blue), showing that this organelle appears not to be affected by the various treatments. The bar indicates 10 μm.