We found that lipid droplets isolated from wild type worms
contained similar lipids that made up the whole worm lipid composition,
but were highly enriched in triacylglycerols (TAG). The major
phospholipid (PL) components consist of phosphatidylcholine (PC)
and phosphatidylethanolamine (PE) (Fig. 1A and B). While wild type
whole worm lipid extracts contain a TAG/PL ratio of 1.2 (±0.2), lipid
droplets contain a TAG/PL ratio of 21.3 (±2.8). The daf-2 mutants
showed an even higher enrichment of TAG stores, with the whole
worm TAG/PL ratio of 1.8 (±0.2) and a TAG/PL ratio in isolated daf-2
lipid droplets of 38.0 (±2.7) (Fig. 1B). Both wild type and daf-2 lipid
droplets have higher PC to PE ratio than whole worm extracts, with a
PC/PE ratio of 3.8 (±0.6) in wild type lipid droplets compared to a 1.3
(±0.1) ratio inwholewormextracts (Fig. 1C). These ratioswere similar
in daf-2 mutant worm and lipid droplet extracts (Fig. 1C). Overall, the
lipid composition in C. elegans lipid droplets is similar to that described
in other systems, in which lipid droplets are enriched in TAGs and the
surrounding phospholipid monolayer is enriched in PC [5,35].
In addition to TAGs, the hydrophobic core of lipid droplets isolated
from mammalian and yeast cells contain relatively high amounts of
sterol esters [36,37]. As indicated by cholesterol staining, C. elegans
membranes contain relatively low levels of sterols [38]. Thin layer