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A more recent version of this article appeared on January 1, 2007
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Submitted on May 22, 2006
Revised on August 24, 2006
Accepted on October 13, 2006
Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark
Monitoring Editor: Sean Munro
Cholesterol is an important constituent of cellular membranes. It has been suggested that cholesterol segregates into sterol-rich and -poor domains in the plasma membrane, though clear evidence for this is lacking. By fluorescence imaging of the natural sterol dehydroergosterol (DHE) the lateral sterol distribution has been visualized in living cells. The spatial labeling pattern of DHE coincided with surface structures like ruffles, microvilli and filopodia with correlation lengths in the range of 0.8-2.5 µm. DHE staining of branched tubules and of nanotubes connecting two cells was detected. Dynamics of DHE in folded and plane membrane regions was comparable as determined by fluorescence recovery after photobleaching (FRAP). DHE colocalized with fluid-membrane preferring phospholipids in surface structures, at sites of cell attachment as well as in the cleavage furrow of dividing cells but was not particularly enriched in those regions. Fluorescent sterol showed homogeneous staining in membrane blebs induced by F-actin disruption. Cross-linking the ganglioside GM1 - a putative raft marker - did not affect the cell surface distribution of DHE. The results suggest that spatial heterogeneities of plasma membrane staining of DHE resolvable by light microscopy reflect the cell surface topography but not phase separated sterol domains in the bilayer plane.
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