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Lipid bodies (LBs) are abundant structures in the cytoplasm of eukaryotic cells. LBs are believed to form within the two leaflets of the membrane of the endoplasmic reticulum and to function as lipid storage sites. LBs consist of a core of apolar lipids (as triacylglycerol or cholesterol esters) encapsulated by a single monolayer of phospholipids and by a dense coat of proteins. Recent studies have provided new insights into trafficking of proteins to LBs. Pol et al. (Mol. Biol. Cell [2004] 15, 99-110) demonstrate that caveolin, a crucial component of plasma membrane caveolae, associates with LBs in a reversible fashion. Moreover, a caveolin mutant modulates lipid body motility and function. Caveolins represent an intriguing system to study how membrane components can dynamically associate with the monolayer of phospholipids that encloses the LBs.

In cultured cells, by the incubation of the cells with fatty acids, such as oleic acid, LBs can be induced to form and accumulate and can then be detected with the dye Nile Red. The central panel of the cover image shows the accumulation of lipids in cells incubated with fatty acids. The upper panel shows how brefeldin A (a drug that disrupts the Golgi complex) causes a rapid redistribution of endogenous caveolins from the Golgi complex to LBs and how this association is reversed upon brefeldin A washout. The lower panel shows how a caveolin dominant negative mutant alters neutral lipid accumulation in LBs, primarily through inhibition of neutral lipid removal from the LB stores after lipid accumulation. Images are by Albert Pol from the above article.