Body composition with respect to white adipose tissue and lean body mass is of central importance and a determining factor of adiposity-associated perturbations, such as diabetes type 2, cardiovascular disease, and cancer. Therefore, modulation of body composition and especially the reduction of body fat are the main foci of dietary and lifestyle interventions. In the last few years, Caenorhabditis elegans became a model organism for investigating fat storage and metabolism, as reviewed by different authors ( 1-3 ). Based on forward genetics ( 4-6 ), functional genomics, and candidate gene approaches ( 7,8 ), more than 400 genes possibly involved in fat storage were described in C. elegans . Most of these genes are evolutionarily conserved and allocated in common pathways and are of relevance for the study of human adiposity.Although C. elegans was extensively used as a model organism to study the genetic and functional basis of fat storage, robust lipid droplet markers such as perilipin are not available at the moment ( 2 ). Appropriate methods concerning the distribution behavior of dyes in the worm or the reproducibility of staining procedures are still under discussion ( 3 ). The classical fi xative Sudan black dye ( 9 ) is shown to be very error prone in C. elegans because of the last ethanol-based washing steps. Recently O' Rourke et al. ( 10 ) demonstrated that the vital dyes Nile red and C1-C12-BODIPY-labeled fatty acid, which were used in more than 75 reports, stain lysosome-like granules rather than lipid droplets within the C. elegans intestine. These dyes were shown not to localize with the fi xative neutral fat fl uorophore LipidTox ( 10 ) 17 March 2011. Published, JLR Papers in Press, March 18, 2011 DOI 10.1194 Fluorescence-based fi xative and vital staining of lipid droplets in Caenorhabditis elegans reveal fat stores using microscopy and fl ow cytometry approaches Abbreviations: BP, bandpass; CARS, coherent anti-Stokes Raman scattering; COPAS, cytometry-based object parametric analysis and sorting system; LRO, lysosome-related organelle; OPO, optical parametric oscillator; TOF, time of fl ight; TAG, triacylglycerol. Manuscript received 8 October 2010 and in revised form

Cytosolic lipid droplets are versatile, evolutionarily conserved organelles that are important for the storage and utilization of lipids in almost all cell types. To obtain insight into the physiological importance of lipid droplet size, we isolated and characterized a new S-adenosyl methionine synthetase 1 (SAMS-1)-deficient Caenorhabditis elegans mutant, which have enlarged lipid droplets throughout its life cycle. We found that the sams-1 mutant showed a markedly reduced body size and progeny number; impaired synthesis of phosphatidylcholine, a major membrane phospholipid; and elevated expression of key lipogenic genes, such as dgat-2, resulting in the accumulation of triacylglyceride in fewer, but larger, lipid droplets. The sams-1 mutant store more than 50 % (wild type: 10 %) of its intestinal fat in large lipid droplets, C10 lm 3 in size. In response to starvation, SAMS-1 deficiency causes reduced depletion of a subset of lipid droplets located in the anterior intestine. Given the importance of liberation of fatty acids from lipid droplets, we propose that the physiological function of SAMS-1, a highly conserved enzyme involved in one-carbon metabolism, is the limitation of fat storage to ensure proper growth and reproduction.