Functions of the Golgi complex in cell division: formation of cell-matrix contacts and cell-cell communication channels in the terminal phase of cytokinesis.

ABSTRACT

The Golgi complex of mammalian cells is disorganized into dispersed vesicular and tubular elements during mitosis and is then reorganized into an interconnected system of cisternal stacks in each daughter cell during cytokinesis. Recent studies further indicate that the Golgi complex is typically relocated from the proximal to the distal side of the nucleus in the terminal phase of cytokinesis (as related to the intercellular bridge). Here, the functional role of this shift in position was approached using rat embryo fibroblasts synchronized with thymidine and nocodazole. Mitotic cells were collected by shaking and seeded in medium without or with brefeldin A (a fungal metabolite that inhibits protein secretion). They were fixed after one or two hours and stained for immunocytochemical demonstration of mannosidase II (a Golgi protein), fibronectin (an extracellular matrix protein), the fibronectin receptor (a member of the integrin family of proteins), and connexin 43 (a member of the connexin family of gap junction proteins). One hour after seeding, the cells had completed mitosis and progressed into cytokinesis. The Golgi complex was now usually located on the proximal side of the nucleus and overlapping fibrillar arrays of fibronectin and fibronectin receptors were observed in the contact zone between the daughter cells, while connexin 43 mainly occurred in fine dispersed spots. Two hours after seeding, the cells had spread out on the substrate and started to move apart. The Golgi complex was now usually located on the distal side of the nucleus. Moreover, fibronectin and fibronectin receptors were found to codistribute both in the contact zone between the daughter cells and in adhesive contacts beneath them, while connexin 43 was concentrated to plaques in the former zone. After treatment with brefeldin A, there was a diffuse cytoplasmic staining for mannosidase II and fibronectin and no distinct extracellular staining for fibronectin was noted. In addition, the connexin 43 positive plaques were reduced in size and number. Although the cells completed cytokinesis in the presence of the drug, they showed an increased tendency to detach from the substrate and locate on top of each other rather than to move apart normally. Taken together, the observations suggest that the change in position of the Golgi complex during cytokinesis serves the function to direct transport of secretory proteins as well as membrane constituents to different parts of the cell surface at different times.(ABSTRACT TRUNCATED AT 400 WORDS)