Fat Body—Multifunctional Insect Tissue

The relationships between corpora allata and fat body and haemolymph lipids in the adult female desert locust

Fat body cells of Amblyomma cajennense partially engorged females (Acari: Ixodidae) and their role on vitellogenesis process

Metabolic shift from lipogenesis to glycogenesis in the last instar larval fat body of the silkworm, Bombyx mori

Metamorphic changes in fat body proteins of the southwestern corn borer, Diatraea grandiosella

The neuro-endocrine control of protein metabolism in the migratory grasshopper, Melanoplus sanguinipes

Synthesis of vitellogenic and non-vitellogenic yolk proteins by the fat body and the ovary of Leptinotarsa decemlineata

This work analyzed the process of lipid storage in fat body of larval Manduca sexta, focusing on the role of lipid transfer particle (LTP). Incubation of fat bodies with [(3)H]diacylglycerol-labeled lipophorin resulted in a significant accumulation of diacylglycerol (DAG) and triacylglycerol (TAG) in the tissue. Transfer of DAG to fat body and its storage as TAG was significantly inhibited (60%) by preincubating the tissue with anti-LTP antibody. Lipid transfer was restored to control values by adding LTP to fat body. Incubation of fat body with dual-labeled DAG lipophorin or its treatment with ammonium chloride showed that neither a membrane-bound lipoprotein lipase nor lipophorin endocytosis is a relevant pathway to transfer or to storage lipids into fat body, respectively. Treatment of fat body with suramin caused a 50% inhibition in [(3)H]DAG transfer from lipophorin. Treatment of [(3)H]DAG-labeled fat body with lipase significantly reduced the amount of [(3)H]DAG associated with the tissue, suggesting that the lipid is still on the external surface of the membrane. Whether this lipid represents irreversibly adsorbed lipophorin or a DAG lipase-sensitive pool is unknown. Nevertheless, these results indicate that the main pathway for DAG transfer from lipophorin to fat body is via LTP and receptor-mediated processes.

Vitellogenin (Vg) synthesis in cultured tissues was analysed biochemically in a soft tick,Ornithodoros moubata. Nine tissue fractions dissected from reproductive females were incubated in vitro in a specially designed Ringer containing35S-methionine. The synthesis of total protein and Vg was assayed by the radioactivity incorporated into precipitates with trichloroacetic acid and antivitellin (Vn)-serum, respectively. Fat body was the most active tissue in Vg synthesis, which comprised 46% of the Vg synthesis by all tissues and 42% of total protein synthesis by fat body. Protein synthesized by the fat body and precipitated with anti-Vn-serum was shown by electrophoresis and fluorography, to consist of six radioactive polypeptides corresponding to the components of Vg. Vg synthesized in cultured fat body was first accumulated in the tissue and secreted into the medium during incubation. Some tissues other than fat body showed low Vg synthesis (in each, less than 12% of total protein synthesis) which, however, may be due to contamination by fat body cells as seen with the scanning electron microscope (SEM). SEM also showed that fat body cells in the active stage of Vg synthesis expanded about 10-fold in length. Immunohistochemical analysis showed a very strong reaction with anti-Vn-IgG in the cytoplasm of fat body from reproductive females. Fat body from unfed females and other tissues including midgut, did not show any specific fluorescence. A positive reaction was obtained with developing oocytes. These results indicate that the fat body is the only site of Vg synthesis in this tick.

Short-term effects of crustecdysone (20-hydroxyecdysone) on protein and RNA synthesis in third instar larvae of Calliphora

Extended longevity lines of Drosophila melanogaster: abundance of yolk protein gene mRNA in fat body and ovary.

THE FAT BODY AS A PROTEIN FACTORY

Secretion and Uptake of 14C Proteins by Fat Body of Calpodes ethlius Stoll. (Lepidoptera, Hesperiidae)

Regulation of lipid homeostasis by the TBC protein dTBC1D22 via modulation of the small GTPase Rab40 to facilitate lipophagy.

Target of rapamycin (TOR), a serine/threonine protein kinase, is involved in yolk protein synthesis in insects besides regulating a number of growth and developmental processes of an organism. p70 S6 kinase (S6K), a serine/threonine protein kinase, is a downstream target of TOR and an important regulator of protein synthesis responsible for cell growth and reproduction. In the present study, two genes, TOR and S6K were isolated and designated as BdTOR (GenBank accession no. FJ167395) and BdS6K (GQ203802), respectively, from the oriental fruit fly, Bactrocera dorsalis (Hendel). Downregulation of BdTOR activity in vivo resulted in a significant reduction in yolk protein transcripts in both fat body and ovary, with a substantial reduction of ovary size. Downregulation of BdS6K activity in the larval stage resulted in the developmental defects of larvae, pupae, and adults with a curtailed yolk protein expression in the fat body throughout the first reproductive cycle with a substantial reduction in ovary size and also repressed the egg development in female fruit fly. All these observations support the involvement of S6K-mediated TOR signaling in the regulation of the yolk protein synthesis and egg development in B. dorsalis. This study also shows that nutrition-mediated larval S6K signaling is important for adult yolk protein expression and egg production in B. dorsalis. Treatment of the female flies with the reproductive hormone, juvenile hormone (JH), significantly increased BdTOR and BdS6K expression, and also Bdyp1 mRNA only in the presence of BdTOR mRNA, in the fat body, indicating that TOR connects the link between JH and yolk protein production.

Two kinds of storage proteins (SP‐1, SP‐2) were confirmed in hemolymph and fat body of Pieris rapae during metamorphosis. Both proteins were present in high concentrations in the hemolymph during the last larval instar. Hemolymph concentrations of SP‐1 and SP‐2 dropped after pupation as the proteins were being deposited in fat bodies. SP‐2 is present in a larger amount than SP‐1. Detailed studies on storage proteins determined their properties, mode of synthesis, and accumulation in the fat body.SP‐1 has a molecular weight of 500,000 and consists of one type of subunit (Mr 77,000), while SP‐2 has a molecular weight of 460,000 and is composed of two types of subunits (Mr 80,000 and 69,000). The pl values of SP‐1 and SP‐2 were determined to be 6.97 and 7.06, respectively.Fat body cells from 1‐day‐old fifth instar larvae synthesized storage proteins in large amounts, whereas those from late prepupae exhibited high protein sequestration. Proteins taken up in fat body accumulated in dense granules during the pupal stage but sharply decreased at the adult stage.Morphological changes in the fat body tissues were observed during the larval‐pupal transformation; the nuclei of fat body cells became irregularly shaped, and the boundaries between cells seemed to be obscure. Synthesis, storage, or degradation of storage proteins in fat body during development is closely associated with morphological changes in the tissues.