The Cytoplasm: Paraplasmic Inclusions
Lipid droplets (LDs) are neutral lipid-containing structures that play an essential role in energy storage and also have additional functions. In addition to being a major structural component of adipocytes (cf. Figs. 164 and 165 ), they are ubiquitous
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confused with contact sites between endoplasmic reticulum and lipid droplets (cf. Fig. 97). Panel G depicts schematically two proposed models of lipid droplet biogenesis. They have in common the presence of a tiny lipid ester droplet between the inner and outer phospholipid leaflet of the ER membrane. This lipid droplet leaves the ER either by a budding-fission process, which is currently widely accepted, or by hatching. In either case, the cytoplasmic phospholipid leaflet forms the surface phospholipid layer of the lipid droplet. Figures A–G from Fujimoto et al. (2008) Histochem Cell Biol 130:263.
References Fujimoto T, Parton RG (2011) Not just fat: the structure and function of the lipid droplet. Cold Spring Harb Perspect Biol 3:a004838 Fujimoto T, Ohsaki Y, Cheng J, Suzuki M, Shinohara Y (2008) Lipid droplets: a classic organelle with new outfits. Histochem Cell Biol 130:263 Ohsaki Y, Cheng J, Suzuki M, Fujita A, Fujimoto T (2008) Lipid droplets are arrested in the ER membrane by tight binding of lipidated apolipoprotein B-100. J Cell Sci 121:2415 Ohsaki Y, Suzuki M, Fujimoto T (2014) Open questions in lipid droplet biology. Chem Biol 21:86 Ozeki S, Cheng J, Tauchi-Sato K, Hatano N, Taniguchi H, Fujimoto T (2005) Rab18 localizes to lipid droplets and induces their close apposition to the endoplasmic reticulum-derived membrane. J Cell Sci 118:2601 Robenek MJ, Severs NJ, Schlattmann K, Plenz G, Zimmer KP, Troyer D, Robenek H (2004) Lipids partition caveolin-1 from ER membranes into lipid droplets: updating the model of lipid droplet biogenesis. FASEB J 18:866 Robenek H, Robenek MJ, Troyer D (2005) PAT family proteins pervade lipid droplet cores. J Lipid Res 46:1331 Robenek H, Hofnagel O, Buers I, Robenek MJ, Troyer D, Severs NJ (2006) Adipophilin-enriched domains in the ER membrane are sites of lipid droplet biogenesis. J Cell Sci 119:4215 Sato S, Fukasawa M, Yamakawa Y, Natsume T, Suzuki T, Shoji I, Aizaki H, Miyamura T, Nishijima M (2006) Proteomic profiling of lipid droplet proteins in hepatoma cell lines expressing hepatitis C virus core protein. J Biochem 139:921 Thiam AR, Farese jr RV, Walther TC (2013) The biophysics and cell biology of lipid droplets. Nat Rev Mol Cell Biol 14:775
Magnification: ×45,000 (A); ×300,000 (B, D); ×32,500 (F) M. Pavelka, J. Roth, Functional Ultrastructure: Atlas of Tissue Biology and Pathology, Third Edition, DOI 10.1007/978-3-7091-1830-6_9, © Springer-Verlag Vienna 2015
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The Cytoplasm: Paraplasmic Inclusions
GLYCOGEN Glucose is an important source for energy, and glycogen is its cellular storage form, which is most abundant in liver and muscle. Glycogen is found in the cytoplasm in the form of granules ranging from 10 to 40 nm in diameter, the so-called β particles, which are typical for muscle cells. In hepatocytes, the β particles assemble to form characteristic rosettes of glycogen, the α particles (arrows). The α particles do not consist solely of glycogen but additionally contain various enzymatic proteins involved in the synthesis of glycoge
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