Diacylglycerol transport in the insect fat body: evidence of involvement of lipid droplets and the cytosolic fraction

In this report we show the existence of a distinct pool of fat body diacylg lycerol (DG) that can be distinguished from the bulk DG. This is a dynamic pool of DG that uses FA entering the fat body from the hemolymph, whereas t he bulk DG uses the fatty acids stored in the fat body fat droplets. Using a dual labeling technique, it was possible to compare the effect of hormone -stimulated DG synthesis and secretion on the distribution of radiolabeled FA among the lipids of the dynamic pool (short-term radiolabeling), with th e hormonal effect on the total complement of fat body lipids (longterm radi olabeling). We observed that, whereas DG represents 2% to 3% of the fat bod y lipid mass, about 20% of the short-term radiolabeled lipids are represent ed by DG. Stimulation of lipolysis produces a fast decrease in the fraction of short-term radiolabeled DG, whereas there is an increase in the mass of fat body DG. The subcellular distribution of bulk DG showed that its major ity (62%) was in the fat cake whereas only 2.9% was in the cytosol. On lipo lysis stimulation, the largest changes in specific activities of newly synt hesized DG were detected in the cytosol and the fat cake, suggesting that n ewly synthesized DG localized in the lipid droplets and the cytosol is pref erentially mobilized.