The gregarious lipid droplet

Cytoplasmic lipid droplets were considered until recently to be in the same category as glycogen granules, simple storage sites for energy, waxing and waning as metabolic energy needs dictated, but otherwise inert particles. It has become clear, however, that droplets are much more than isolated storage depots in the cell and that they can skate around on the cytoskeleton, physically interact with several organelles over short or long durations, and be beasts of burden, storing important molecules unrelated to lipids for later use. Although important clues to the panoply of droplet functions have come to light as a result of several proteomics studies, some behavioral qualities of this organelle were apparent from older morphological studies. Droplets are indeed gregarious. In this Minireview, after first considering the basic biochemical properties of lipid droplets, I shall focus on their interactions with other organelles, as manifest by morphological and dynamic studies and hinted at by proteomics. The important functions of droplets in storing and chaperoning proteins are well covered in a recent review (1) and will not be discussed here.