Lipid droplets as fat storage organelles in Caenorhabditis elegans
2011; Elsevier BV; Volume: 53; Issue: 1 Linguagem: Inglês
10.1194/jlr.r021006
ISSN1539-7262
Autores Tópico(s)Genetics, Aging, and Longevity in Model Organisms
ResumoLipid droplets are evolutionarily conserved organelles where cellular fat storage and mobilization are exquisitely regulated. Recent studies have defined lipid droplets in C. elegans and explored how they are regulated by genetic and dietary factors. C. elegans offers unique opportunities to visualize lipid droplets at single-cell resolution in live animals. The development of novel microscopy techniques and protein markers for lipid droplets will accelerate studies on how nutritional states and subcellular organization are linked in vivo. Together with powerful tools for genetic and biochemical analysis of metabolic pathways, alteration in lipid droplet abundance, size, and distribution in C. elegans can be readily connected to whole-animal energy homeostasis, behavior, and life span. Therefore, further studies on lipid droplets in C. elegans promise to yield valuable insights that complement our knowledge gained from yeast, Drosophila, and mammalian systems on cellular and organismal fat storage. Lipid droplets are evolutionarily conserved organelles where cellular fat storage and mobilization are exquisitely regulated. Recent studies have defined lipid droplets in C. elegans and explored how they are regulated by genetic and dietary factors. C. elegans offers unique opportunities to visualize lipid droplets at single-cell resolution in live animals. The development of novel microscopy techniques and protein markers for lipid droplets will accelerate studies on how nutritional states and subcellular organization are linked in vivo. Together with powerful tools for genetic and biochemical analysis of metabolic pathways, alteration in lipid droplet abundance, size, and distribution in C. elegans can be readily connected to whole-animal energy homeostasis, behavior, and life span. Therefore, further studies on lipid droplets in C. elegans promise to yield valuable insights that complement our knowledge gained from yeast, Drosophila, and mammalian systems on cellular and organismal fat storage. Lipid droplets are ubiquitous fat storage organelles that are conserved in yeast, C. elegans, Drosophila, and mammals (1.Farese Jr, R.V. Walther T.C. Lipid droplets finally get a little R-E-S-P-E-C-T.Cell. 2009; 139: 855-860Abstract Full Text Full Text PDF PubMed Scopus (695) Google Scholar, 2.Goodman J.M. Demonstrated and inferred metabolism associated with cytosolic lipid droplets.J. Lipid Res. 2009; 50: 2148-2156Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar, 3.Martin S. Parton R.G. Lipid droplets: a unified view of a dynamic organelle.Nat. Rev. Mol. Cell Biol. 2006; 7: 373-378Crossref PubMed Scopus (914) Google Scholar). They are also sites of regulated release of stored fat by lipases during cell growth and fasting (4.Zechner R. Kienesberger P.C. Haemmerle G. Zimmermann R. Lass A. Adipose triglyceride lipase and the lipolytic catabolism of cellular fat stores.J. Lipid Res. 2009; 50: 3-21Abstract Full Text Full Text PDF PubMed Scopus (404) Google Scholar). Therefore, lipid droplets are central to energy balance at cellular and organismal levels. Key structural and biochemical features of lipid droplets have been defined, and it is generally accepted that neutral lipids such as triglycerides (TAG) and cholesterol esters (CE) are stored in the interior of the organelle that is delimited by a phospholipid monolayer (5.Blanchette-Mackie E.J. Dwyer N.K. Barber T. Coxey R.A. Takeda T. Rondinone C.M. Theodorakis J.L. Greenberg A.S. Londos C. Perilipin is located on the surface layer of intracellular lipid droplets in adipocytes.J. Lipid Res. 1995; 36: 1211-1226Abstract Full Text PDF PubMed Google Scholar, 6.Robenek H. Buers I. Hofnagel O. Robenek M.J. Troyer D. Severs N.J. Compartmentalization of proteins in lipid droplet biogenesis.Biochim. Biophys. Acta. 2009; 1791: 408-418Crossref PubMed Scopus (65) Google Scholar, 7.Tauchi-Sato K. Ozeki S. Houjou T. Taguchi R. Fujimoto T. The surface of lipid droplets is a phospholipid monolayer with a unique fatty acid composition.J. Biol. Chem. 2002; 277: 44507-44512Abstract Full Text Full Text PDF PubMed Scopus (517) Google Scholar). Current models suggest that fatty acid influx can be accommodated by neutral lipid synthesis and a concomitant change in lipid droplet size or number in a tissue-specific manner (1.Farese Jr, R.V. Walther T.C. 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To study regulators of fat storage and lipid droplet size in metazoans, most studies have focused on the use of tissue culture cells and overexpressed lipid droplet-associated proteins or vital dyes as markers. These studies yielded important insights into how conserved proteins and signaling pathways are coupled to control cellular fat storage. Nevertheless, extension of observations made in tissue culture cells into whole-animal models is often time consuming and can lead to surprising results. In the last few years, C. elegans has emerged as an attractive model for studying fat storage in vivo (11.Watts J.L. Fat synthesis and adiposity regulation in Caenorhabditis elegans.Trends Endocrinol. Metab. 2009; 20: 58-65Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar, 12.Mullaney B.C. Ashrafi K. C. elegans fat storage and metabolic regulation.Biochim. Biophys. Acta. 2009; 1791: 474-478Crossref PubMed Scopus (80) Google Scholar). Although C. elegans lacks dedicated adipose tissues, its intestine serves as the main site for fat storage. Yolk lipoproteins are synthesized in the intestine, exported into the body cavity (pseudocoelomic space), and taken up by developing oocytes (13.Grant B. Hirsh D. Receptor-mediated endocytosis in the Caenorhabditis elegans oocyte.Mol. Biol. Cell. 1999; 10: 4311-4326Crossref PubMed Scopus (457) Google Scholar, 14.Hall D.H. Winfrey V.P. Blaeuer G. Hoffman L.H. Furuta T. Rose K.L. Hobert O. Greenstein D. Ultrastructural features of the adult hermaphrodite gonad of Caenorhabditis elegans: relations between the germ line and soma.Dev. Biol. 1999; 212: 101-123Crossref PubMed Scopus (239) Google Scholar, 15.Kimble J. Sharrock W.J. Tissue-specific synthesis of yolk proteins in Caenorhabditis elegans.Dev. Biol. 1983; 96: 189-196Crossref PubMed Scopus (216) Google Scholar). This is remarkably similar to yolk deposition in chicken, where yolk is synthesized in the liver and transported to the ovum via the bloodstream (16.Schneider W.J. Vitellogenin receptors: oocyte-specific members of the low-density lipoprotein receptor supergene family.Int. Rev. Cytol. 1996; 166: 103-137Crossref PubMed Google Scholar). Therefore, the C. elegans intestine may be viewed as a multifunctional organ that fulfills the roles of the liver and adipose tissues. Inspection of the sequenced genome of C. elegans and functional studies through analysis of genetic mutants revealed extensive conservation of genes involved in fatty acid synthesis, elongation, desaturation, and degradation (17.Mak H.Y. Nelson L.S. Basson M. Johnson C.D. Ruvkun G. Polygenic control of Caenorhabditis elegans fat storage.Nat. Genet. 2006; 38: 363-368Crossref PubMed Scopus (156) Google Scholar, 18.Kniazeva M. Crawford Q.T. Seiber M. Wang C.Y. Han M. 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Ruvkun G. daf-2, an insulin receptor-like gene that regulates longevity and diapause in Caenorhabditis elegans.Science. 1997; 277: 942-946Crossref PubMed Scopus (1719) Google Scholar). A number of reverse genetic techniques will accelerate functional dissection of signaling and protein interaction networks (30.Frøkjaer-Jensen C. Davis M.W. Hollopeter G. Taylor J. Harris T.W. Nix P. Lofgren R. Prestgard-Duke M. Bastiani M. Moerman D.G. et al.Targeted gene deletions in C. elegans using transposon excision.Nat. Methods. 2010; 7: 451-453Crossref PubMed Scopus (74) Google Scholar, 31.Kamath R.S. Martinez-Campos M. Zipperlen P. Fraser A.G. Ahringer J. Effectiveness of specific RNA-mediated interference through ingested double-stranded RNA in Caenorhabditis elegans.Genome Biol. 2001; 2 (RESEARCH0002)PubMed Google Scholar, 32.Robert V. Bessereau J.L. Targeted engineering of the Caenorhabditis elegans genome following Mos1-triggered chromosomal breaks.EMBO J. 2007; 26: 170-183Crossref PubMed Scopus (86) Google Scholar). The development of novel transgenic technologies has also enabled expression of native or heterologous proteins to near-physiological levels (33.Frøkjaer-Jensen C. Davis M.W. Hopkins C.E. Newman B.J. Thummel J.M. Olesen S.P. Grunnet M. Jorgensen E.M. Single-copy insertion of transgenes in Caenorhabditis elegans.Nat. Genet. 2008; 40: 1375-1383Crossref PubMed Scopus (716) Google Scholar). This is critical for structure-function analysis of specific proteins in vivo and the accurate targeting of fluorescent protein markers to lipid droplets and other subcellular organelles. The use of C. elegans offers a unique advantage of imaging lipid droplets in live animals at single-cell resolution. Their intestinal cells support lipid droplet expansion to >10 µm in diameter, similar to lipid droplets found in mammalian adipocytes (34.Zhang S.O. Box A.C. Xu N. Le Men J. Yu J. Guo F. Trimble R. Mak H.Y. Genetic and dietary regulation of lipid droplet expansion in Caenorhabditis elegans.Proc. Natl. Acad. Sci. USA. 2010; 107: 4640-4645Crossref PubMed Scopus (113) Google Scholar). In contrast, adherent tissue culture cells have limited depth, which restricts spherical expansion of lipid droplets. Finally, C. elegans offers ample opportunities to connect alteration in cellular fat storage to whole-animal physiology, behavior, and life span (18.Kniazeva M. Crawford Q.T. Seiber M. Wang C.Y. Han M. Monomethyl branched-chain fatty acids play an essential role in Caenorhabditis elegans development.PLoS Biol. 2004; 2: E257Crossref PubMed Scopus (146) Google Scholar, 35.Brock T.J. Browse J. Watts J.L. Genetic regulation of unsaturated fatty acid composition in C. elegans.PLoS Genet. 2006; 2: e108Crossref PubMed Scopus (175) Google Scholar, 36.Wang M.C. O'Rourke E.J. Ruvkun G. Fat metabolism links germline stem cells and longevity in C. elegans.Science. 2008; 322: 957-960Crossref PubMed Scopus (284) Google Scholar). This review will focus on the discovery of lipid droplets in C. elegans, the methods to detect lipid droplets, and the proteins that associate with lipid droplets in this model organism. Thorough understanding of these areas will no doubt provide answers to fundamental questions regarding how lipid droplets accommodate changes in the cellular demand and supply of fat in an evolutionarily conserved manner. In the absence of a specialized fat storage tissue, C. elegans store their fat primarily in the intestine. It is remarkable that the entire intestine is composed of only 20 cells, arranged in rings of two or four cells that enclose the lumen, which spans almost the entire length of the animal (∼1 mm) (37.Leung B. Hermann G.J. Priess J.R. Organogenesis of the Caenorhabditis elegans intestine.Dev. Biol. 1999; 216: 114-134Crossref PubMed Scopus (205) Google Scholar, 38.Altun Z.F. Hall D.H. Alimentary system: intestine.2009Google Scholar). Each intestinal cell is derived from a single embryonic blastomere; cell division ceases and organogenesis is complete before the hatching of a free-living animal (37.Leung B. Hermann G.J. Priess J.R. Organogenesis of the Caenorhabditis elegans intestine.Dev. Biol. 1999; 216: 114-134Crossref PubMed Scopus (205) Google Scholar, 38.Altun Z.F. Hall D.H. Alimentary system: intestine.2009Google Scholar). Nevertheless, the intestinal cells increase in size that matches the growth of the animal as it progresses through four larval stages before maturing into a reproductive adult. One of the defining features of lipid droplets is the phospholipid monolayer that encloses their neutral lipid core, as demonstrated by transmission and freeze-fracture electron microscopy (5.Blanchette-Mackie E.J. Dwyer N.K. Barber T. Coxey R.A. Takeda T. Rondinone C.M. Theodorakis J.L. Greenberg A.S. Londos C. Perilipin is located on the surface layer of intracellular lipid droplets in adipocytes.J. Lipid Res. 1995; 36: 1211-1226Abstract Full Text PDF PubMed Google Scholar, 6.Robenek H. Buers I. Hofnagel O. Robenek M.J. Troyer D. Severs N.J. Compartmentalization of proteins in lipid droplet biogenesis.Biochim. Biophys. Acta. 2009; 1791: 408-418Crossref PubMed Scopus (65) Google Scholar, 7.Tauchi-Sato K. Ozeki S. Houjou T. Taguchi R. Fujimoto T. The surface of lipid droplets is a phospholipid monolayer with a unique fatty acid composition.J. Biol. Chem. 2002; 277: 44507-44512Abstract Full Text Full Text PDF PubMed Scopus (517) Google Scholar). This sets lipid droplets apart from all other intracellular organelles that are bound by a phospholipid bilayer. Extensive ultrastructural studies have been performed in C. elegans that revealed numerous vesicular compartments of similar size in the intestinal cells (37.Leung B. Hermann G.J. Priess J.R. Organogenesis of the Caenorhabditis elegans intestine.Dev. Biol. 1999; 216: 114-134Crossref PubMed Scopus (205) Google Scholar, 38.Altun Z.F. Hall D.H. Alimentary system: intestine.2009Google Scholar, 39.Albert P.S. Riddle D.L. Mutants of Caenorhabditis elegans that form dauer-like larvae.Dev. Biol. 1988; 126: 270-293Crossref PubMed Scopus (89) Google Scholar). These compartments may be differentiated by their electron densities. Two putative fat and lipoprotein storage compartments have been proposed: electron-lucent lipid droplets and electron-opaque gut granules (37.Leung B. Hermann G.J. Priess J.R. Organogenesis of the Caenorhabditis elegans intestine.Dev. Biol. 1999; 216: 114-134Crossref PubMed Scopus (205) Google Scholar, 38.Altun Z.F. Hall D.H. Alimentary system: intestine.2009Google Scholar, 39.Albert P.S. Riddle D.L. Mutants of Caenorhabditis elegans that form dauer-like larvae.Dev. Biol. 1988; 126: 270-293Crossref PubMed Scopus (89) Google Scholar, 40.Zhang S.O. Trimble R. Guo F. Mak H.Y. Lipid droplets as ubiquitous fat storage organelles in C. elegans.BMC Cell Biol. 2010; 11: 96Crossref PubMed Scopus (80) Google Scholar). Gut granules have also been detected using light microscopy and were subsequently defined as lysosome-related organelles (LRO) (41.Clokey G.V. Jacobson L.A. The autofluorescent "lipofuscin granules" in the intestinal cells of Caenorhabditis elegans are secondary lysosomes.Mech. Ageing Dev. 1986; 35: 79-94Crossref PubMed Scopus (151) Google Scholar, 42.Hermann G.J. Schroeder L.K. Hieb C.A. Kershner A.M. Rabbitts B.M. Fonarev P. Grant B.D. Priess J.R. Genetic analysis of lysosomal trafficking in Caenorhabditis elegans.Mol. Biol. Cell. 2005; 16: 3273-3288Crossref PubMed Scopus (181) Google Scholar). The appearance and relative abundance of these compartments are dependent on the developmental stages of the animal. However, membrane structures that surrounded these compartments were not studied in detail until recently. To positively identify lipid droplets using electron microscopy in C. elegans, Zhang et al. took advantage of a mutant that appeared to undergo selective expansion of fat storage compartments (34.Zhang S.O. Box A.C. Xu N. Le Men J. Yu J. Guo F. Trimble R. Mak H.Y. Genetic and dietary regulation of lipid droplet expansion in Caenorhabditis elegans.Proc. Natl. Acad. Sci. USA. 2010; 107: 4640-4645Crossref PubMed Scopus (113) Google Scholar) (Fig. 1). The daf-22/thiolase gene encodes the terminal enzyme in a peroxisomal β-oxidation pathway. DAF-22/thiolase was originally identified as a key enzyme for processing the fatty acid moiety of the C. elegans dauer pheromone (43.Butcher R.A. Ragains J.R. Li W. Ruvkun G. Clardy J. Mak H.Y. Biosynthesis of the Caenorhabditis elegans dauer pheromone.Proc. Natl. Acad. Sci. USA. 2009; 106: 1875-1879Crossref PubMed Scopus (122) Google Scholar). Loss of DAF-22/thiolase function in C. elegans specifically increases the level of triglycerides that are accommodated by expanded fat storage compartments in the intestinal cells (34.Zhang S.O. Box A.C. Xu N. Le Men J. Yu J. Guo F. Trimble R. Mak H.Y. Genetic and dietary regulation of lipid droplet expansion in Caenorhabditis elegans.Proc. Natl. Acad. Sci. USA. 2010; 107: 4640-4645Crossref PubMed Scopus (113) Google Scholar). As most other vesicular structures are 10 µm in diameter) could be readily identified by size. Indeed, it was found that such compartments were delimited by a phospholipid monolayer, thus confirming the existence of lipid droplets in C. elegans (34.Zhang S.O. Box A.C. Xu N. Le Men J. Yu J. Guo F. Trimble R. Mak H.Y. Genetic and dietary regulation of lipid droplet expansion in Caenorhabditis elegans.Proc. Natl. Acad. Sci. USA. 2010; 107: 4640-4645Crossref PubMed Scopus (113) Google Scholar). Additional support came from the targeting of the adipose triglyceride lipase (ATGL) ortholog ATGL-1 to the surface of expanded lipid droplets in daf-22 mutant animals (34.Zhang S.O. Box A.C. Xu N. Le Men J. Yu J. Guo F. Trimble R. Mak H.Y. Genetic and dietary regulation of lipid droplet expansion in Caenorhabditis elegans.Proc. Natl. Acad. Sci. USA. 2010; 107: 4640-4645Crossref PubMed Scopus (113) Google Scholar). Since the initial report, lipid droplets have also been identified in wild-type animals by transmission electron microscopy (40.Zhang S.O. Trimble R. Guo F. Mak H.Y. Lipid droplets as ubiquitous fat storage organelles in C. elegans.BMC Cell Biol. 2010; 11: 96Crossref PubMed Scopus (80) Google Scholar). It was also determined that lipid droplets are distinct from LROs (40.Zhang S.O. Trimble R. Guo F. Mak H.Y. Lipid droplets as ubiquitous fat storage organelles in C. elegans.BMC Cell Biol. 2010; 11: 96Crossref PubMed Scopus (80) Google Scholar), a compartment that was previously proposed to store fat in C. elegans (44.Schroeder L.K. Kremer S. Kramer M.J. Currie E. Kwan E. Watts J.L. Lawrenson A.L. Hermann G.J. Function of the Caenorhabditis elegans ABC transporter PGP-2 in the biogenesis of a lysosome-related fat storage organelle.Mol. Biol. Cell. 2007; 18: 995-1008Crossref PubMed Scopus (90) Google Scholar). Furthermore, expanded lipid droplets have been reported in mutant animals that lack ACS-3/acyl-CoA synthetase (45.Mullaney B.C. Blind R.D. Lemieux G.A. Perez C.L. Elle I.C. Faergeman N.J. Van Gilst M.R. Ingraham H.A. Ashrafi K. Regulation of C. elegans fat uptake and storage by acyl-CoA synthase-3 is dependent on NR5A family nuclear hormone receptor nhr-25.Cell Metab. 2010; 12: 398-410Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar). Attempts to visualize and quantitate fat storage long preceded the definitive identification of lipid droplets in C. elegans. Sudan Black has been widely adopted as a stain for intracellular fat since its first usage on bacteria (46.Burdon K.L. Stokes J.C. Kimbrough C.E. Studies of the common aerobic spore-forming bacilli: I. Staining for fat with Sudan Black B-safranin.J. Bacteriol. 1942; 43: 717-724Crossref PubMed Google Scholar). In C. elegans, animals that expressed a defective insulin/IGF receptor ortholog DAF-2 showed more intense Sudan Black staining than wild-type animals (29.Kimura K.D. Tissenbaum H.A. Liu Y. Ruvkun G. daf-2, an insulin receptor-like gene that regulates longevity and diapause in Caenorhabditis elegans.Science. 1997; 277: 942-946Crossref PubMed Scopus (1719) Google Scholar). Subsequent biochemical measurement confirmed that loss of insulin signaling elevated triglyceride levels in C. elegans, validating Sudan Black staining as a method for visualization of fat storage (47.Ashrafi K. Chang F.Y. Watts J.L. Fraser A.G. Kamath R.S. Ahringer J. Ruvkun G. Genome-wide RNAi analysis of Caenorhabditis elegans fat regulatory genes.Nature. 2003; 421: 268-272Crossref PubMed Scopus (832) Google Scholar). Sudan Black staining was most prominent in intestinal cells, thus giving rise to the notion that the intestine is the major fat storage organ in C. elegans. In addition, Sudan Black staining was observed in the hypodermis and gonad, suggesting that fat is exported from the intestine to other tissues. Although Sudan Black staining was widely employed in other studies (27.Sze J.Y. Victor M. Loer C. Shi Y. Ruvkun G. Food and metabolic signalling defects in a Caenorhabditis elegans serotonin-synthesis mutant.Nature. 2000; 403: 560-564Crossref PubMed Scopus (477) Google Scholar, 48.Ogg S. Paradis S. Gottlieb S. Patterson G.I. Lee L. Tissenbaum H.A. Ruvkun G. The Fork head transcription factor DAF-16 transduces insulin-like metabolic and longevity signals in C. elegans.Nature. 1997; 389: 994-999Crossref PubMed Scopus (1540) Google Scholar, 49.Ogg S. Ruvkun G. The C. elegans PTEN homolog, DAF-18, acts in the insulin receptor-like metabolic signaling pathway.Mol. Cell. 1998; 2: 887-893Abstract Full Text Full Text PDF PubMed Scopus (330) Google Scholar, 50.McKay R.M. McKay J.P. Avery L. Graff J.M. C elegans: a model for exploring the genetics of fat storage.Dev. Cell. 2003; 4: 131-142Abstract Full Text Full Text PDF PubMed Scopus (248) Google Scholar), the fixation protocol was not readily adaptable for large-scale genetic and functional genomic screens. To overcome this, Nile Red and BODIPY-conjugated fatty acid were used as alternatives for fat staining in live animals (47.Ashrafi K. Chang F.Y. Watts J.L. Fraser A.G. Kamath R.S. Ahringer J. Ruvkun G. Genome-wide RNAi analysis of Caenorhabditis elegans fat regulatory genes.Nature. 2003; 421: 268-272Crossref PubMed Scopus (832) Google Scholar). Nile Red was first introduced as a fluorescent vital stain for intracellular lipid droplets in mammalian cells (51.Greenspan P. Mayer E.P. Fowler S.D. Nile red: a selective fluorescent stain for intracellular lipid droplets.J. Cell Biol. 1985; 100: 965-973Crossref PubMed Scopus (1854) Google Scholar), whereas BODIPY-conjugated fatty acid had been used to monitor fatty acid uptake in mammalian cells (52.Schaffer J.E. Lodish H.F. Expression cloning and characterization of a novel adipocyte long chain fatty acid transport protein.Cell. 1994; 79: 427-436Abstract Full Text PDF PubMed Scopus (743) Google Scholar). It was assumed that worms would ingest Nile Red or BODIPY-conjugated fatty acid from E. coli that had been grown in the presence of these dyes on agar plates. This was followed by absorption of the dyes through the intestinal epithelium and their accumulation in fat storage compartments in intestinal cells. The precise mechanisms of absorption and turnover of these dyes are currently unknown. Nile Red staining was initially used to conduct a whole-genome RNAi screen, which resulted in the discovery of hundreds of gene inactivations that altered the intensity and/or pattern of staining within intestinal cells (47.Ashrafi K. Chang F.Y. Watts J.L. Fraser A.G. Kamath R.S. Ahringer J. Ruvkun G. Genome-wide RNAi analysis of Caenorhabditis elegans fat regulatory genes.Nature. 2003; 421: 268-272Crossref PubMed Scopus (832) Google Scholar). Many genes with conserved function in fat metabolism were uncovered, suggesting that Nile Red staining might serve as an indicator of fat storage in C. elegans. However, recent evidence suggests that vital staining with Nile Red and BODIPY-conjugated fatty acid also illuminates LROs, and that their accumulation in lipid droplets is highly dependent on genetic backgrounds (40.Zhang S.O. Trimble R. Guo F. Mak H.Y. Lipid droplets as ubiquitous fat storage organelles in C. elegans.BMC Cell Biol. 2010; 11: 96Crossref PubMed Scopus (80) Google Scholar, 44.Schroeder L.K. Kremer S. Kramer M.J. Currie E. Kwan E. Watts J.L. Lawrenson A.L. Hermann G.J. Function of the Caenorhabditis elegans ABC transporter PGP-2 in the biogenesis of a lysosome-related fat storage organelle.Mol. Biol. Cell. 2007; 18: 995-1008Crossref PubMed Scopus (90) Google Scholar, 53.Märck C. Olsen L. Kurth C. Persson A. Storm N.J. Svensson E. Jansson J.O. Hellqvist M. Enejder A. Faergeman N.J. et al.Statins inhibit protein lipidation and induce the unfolded protein response in the non-sterol producing nematode Caenorhabditis elegans.Proc. Natl. Acad. Sci. USA. 2009; 106: 18285-18290Crossref PubMed Scopus (75) Google Scholar, 54.Yen K. Le T.T. Bansal A. Narasimhan S.D. Cheng J.X. Tissenbaum H.A. 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Lipid droplets as ubiquitous fat storage organelles in C. elegans.BMC Cell Biol. 2010; 11: 96Crossref PubMed Scopus (80) Google Scholar, 45.Mullaney B.C. Blind R.D. Lemieux G.A. Perez C.L. Elle I.C. Faergeman N.J. Van Gilst M.R. Ingraham H.A. Ashrafi K. Regulation of C. elegans fat uptake and storage by acyl-CoA synthase-3 is dependent on NR5A family nuclear hormone receptor nhr-25.Cell Metab. 2010; 12: 398-410Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar). This is because Nile Red in a neutral lipid environment (i.e., lipid droplets) will emit yellow-gold fluorescence instead of red fluorescence (51.Greenspan P. Mayer E.P. Fowler S.D. Nile red: a selective fluorescent stain for intracellular lipid droplets.J. Cell Biol. 1985; 100: 965-973Crossref PubMed Scopus (1854) Google Scholar). Note that Nile Red, BODIPY, or Oil-Red-O staining on fixed C. elegans samples appears to faithfully highlight lipid droplets and reflect biochemical measurements
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