Developmental changes in the protein composition of Manduca sexta lipid droplets

Abstract

The lipid droplets (LDs) are intracellular organelles mainly dedicated to the storage and provision of fatty acids. To accomplish these functions the LDs interact with other organelles and cytosolic proteins. In order to explore possible correlations between the physiological states of cells and the protein composition of LDs we have determined and compared the proteomic profiles of lipid droplets isolated from the fat bodies of 5th-instar larvae and adult Manduca sexta insects and from ovaries. These LD-rich tissues represent three clearly distinct metabolic states in regard to lipid metabolism: 1) Larval fat body synthesizes fatty acids (FA) and accumulates large amounts as triglyceride (TG); 2) Fat body from adult insects provides FA to support reproduction and flight; 3) Ovaries do not synthesize FA, but accumulate considerable amounts of TG in LDs. Major qualitative and semi-quantitative variations in the protein compositions of the LDs isolated from these three tissues were observed by MS/MS and partially validated by immuno-blotting. The differences observed included changes in the abundance of lipid droplet specific proteins, cytosolic proteins, mitochondrial proteins and also proteins associated with the machinery of protein synthesis. These results suggest that changes in the interaction of LDs with other organelles and cytosolic proteins are tightly related to the physiological state of cells. Herein, we summarize and compare the protein compositions of three subtypes of LDs and also describe for the first time the proteomic profile of LDs from an insect ovary. The compositions and compositional differences found among the LDs are discussed to provide a platform for future studies on the role of LDs, and their associated proteins, in cellular metabolism.

The proteomics of lipid droplets: structure, dynamics, and functions of the organelle conserved from bacteria to humans

“…In addition, the proteomic study of RHA1 identifi ed many ribosomal proteins and transcriptional regulators in isolated lipid droplets ( 41 ), similar to lipid droplet proteomes of other organisms ( 15,18,19,30,33,36,38 ). These data suggest that lipid droplets may provide intracellular membrane system for compartmentalization of cellular activities of certain bacteria.…”

“…During analysis of isolated lipid droplet protein phosphorylation, B. mori Lsd1 (Bmlsd1) was identifi ed ( 32 ). More detailed proteomics was carried out using another insect species Manduca sexta ( M. sexta ) ( 33 ). The study involved three subtypes of lipid droplets that were isolated from the fat bodies of Manduca larvae and adult insects, as well as from Manduca ovary.…”

“…The study involved three subtypes of lipid droplets that were isolated from the fat bodies of Manduca larvae and adult insects, as well as from Manduca ovary. Very similar to lipid droplet-associated proteins in other organisms , M. sexta lipid droplet-associated proteins include lipid synthetic and metabolic enzymes, membranetraffi cking proteins, and cell signaling proteins ( 33 ). Several apolipoproteins were identifi ed as components of M. sexta lipid droplets, raising an interesting question about whether apolipoprotein particles in mammals originally had roles in lipid droplets.…”

As the fat flies: The dynamic lipid droplets of Drosophila embryos

“…6D). Over longer time frames, the droplet protein content likely changes more dramatically: proteomic analyses of larval fat-body and of embryonic droplets show massive differences [15, 37, 61], and direct comparisons of the droplet proteome of different life stages of the moth Manduca sexta [146] reveal major remodeling across development.…”

“…In contrast, in S2 cells, a common Drosophila cultured cell line, histones were not detected on lipid droplets [15, 140]. Finally, proteomic analysis of various life stages of the moth Manduca sexta [146] revealed the presence of H2A, H2B, and H4, but relative amounts varied with developmental stage.…”