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* Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of
Health, Bethesda, Maryland 20892; The Golgi complex is a dynamic organelle
engaged in both secretory and retrograde membrane
traffic. Here, we use green fluorescent protein-Golgi
protein chimeras to study Golgi morphology in vivo. In
untreated cells, membrane tubules were a ubiquitous,
prominent feature of the Golgi complex, serving both
to interconnect adjacent Golgi elements and to carry
membrane outward along microtubules after detaching
from stable Golgi structures. Brefeldin A treatment, which reversibly disassembles the Golgi complex, accentuated tubule formation without tubule detachment.
A tubule network extending throughout the cytoplasm
was quickly generated and persisted for 5-10 min until
rapidly emptying Golgi contents into the ER within 15-30 s. Both lipid and protein emptied from the Golgi
at similar rapid rates, leaving no Golgi structure behind, indicating that Golgi membranes do not simply
mix but are absorbed into the ER in BFA-treated cells.
The directionality of redistribution implied Golgi membranes are at a higher free energy state than ER membranes. Analysis of its kinetics suggested a mechanism
that is analogous to wetting or adsorptive phenomena
in which a tension-driven membrane flow supplements
diffusive transfer of Golgi membrane into the ER. Such
nonselective, flow-assisted transport of Golgi membranes into ER suggests that mechanisms that regulate
retrograde tubule formation and detachment from the
Golgi complex are integral to the existence and maintenance of this organelle.
National Institute of Neurological Disorders and Stroke, NIH, Bethesda, Maryland 20892; § Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06032; and Department of
Physics, Cornell University, Ithaca, New York 14853
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