As in other organisms, isolated C. elegans lipid droplets are composed
of a monolayer of the phospholipids PC and PE, surrounding a core of
neutral lipids consisting almost exclusively of TAGs. Unlike in mammals,
we found that C. elegans lipid droplets contain very little cholesterol or
cholesterol esters. There are similarities in the lipid composition of
C. elegans lipid droplets and yolk particles, which are structurally similar
to mammalian lipoproteins [48]. In C. elegans, both lipid droplets and
yolk particles contain mainly PC and PE as major phospholipid species,
and both contain TAGs, but very little cholesterol or cholesterol esters.
Yolk and lipid droplets differ in that yolk contains large amounts of
vitellogenins, which are apoliproteins that contain relatively higher ratios
of phospholipids to TAGs [48]. The lipid droplet proteomes of our
study and Zhang et al. both showed vitellogenin proteins associated
with lipid droplets, which might indicate an association of lipid droplets
and yolk particles during yolk biogenesis.