Sequestration of Protein by the Fat Body of an Insect

Abstract

THE fat body in an insect commonly contains a single cell type which is functionally diverse. At various times it stores and mobilizes fat, protein and glycogen which it may have synthesized or sequestered. In general the fat body becomes filled with reserves as metamorphosis approaches¹. Larvae of Aëdes fed on casein build up reserves of protein granules in the fat body², and in Drosophila larvae, protein granules are induced to form in the middle of the third stadium by a hormone from the ring gland³. In Calpodes larvae the protein granules are probably translocated endocuticle. They arise suddenly within the Golgi vesicles 30–35 h before pupation, at a time when the thick larval endocuticle is being resorbed by the moulting fluid. At about 10 h before pupation other granules containing both protein and ribosomes arise from the isolation of endoplasmic reticulum in cytolysomes⁴. Although the formation and occurrence of protein granules in the fat body are well documented, there is little information on the origin of the protein.