ACTIN MICROFILAMENTS ARE ESSENTIAL FOR THE CYTOLOGICAL POSITIONING AND MORPHOLOGY OF THE GOLGI-COMPLEX

The organization and function of the Golgi complex was studied in norm al rat kidney cells following disruption of the actin cytoskeleton ind uced by cytochalasin D. In cells treated with these reagents, the reti cular and perinuclear Golgi morphology acquired a cluster shape restri cted to the centrosome region. Golgi complex alteration affected all G olgi subcompartments as revealed by double fluorescence staining with antibodies to the cis/middle Mannosidase II and the trans-Golgi networ k TGN38 proteins or vital staining with the lipid derivate C-6-NBD-cer amide. The ultrastructural and stereological analysis showed that the Golgi cisternae remained attached in a stacked conformation, but they were swollen and contained electron-dense intra-cisternal bodies, The Golgi complex cluster remained linked to microtubules since it was fra gmented and dispersed after treatment with nocodazole. Moreover, the r eassembly of Golgi fragments after the disruption of the microtubuli w ith nocodazole does not utilize the actin microfilaments. The actin mi crofilament requirement for the disassembly and reassembly of the Golg i complex and for the ER-Golgi vesicular transport were also studied. The results show that actin microfilaments are not needed for either t he retrograde fusion of the Golgi complex with the endoplasmic reticul um promoted by brefeldin A or the anterograde reassembly after the rem oval of the drug, or the ER-Golgi transport of VSV-G glycoprotein. How ever, actin microfilaments are directly involved in the subcellular lo calization and the morphology of the Golgi complex.