Establishment of a lipid accumulation model in an insect cell line

The study of adipocyte differentiation and lipid accumulation in insects has been limited by the lack of a system suitable for analysis of molecular mechanisms. Here, we describe the establishment of a model system of lipid accumulation in BmN4 cells, which are derived from silkworm ovary. In BmN4 cells, dexamethasone treatment induced accumulation of lipid, suppressed cellular proliferation, and caused the cells to form aggregates. We isolated the Bombyx mori fatty acid binding protein 1 gene (BmFABP1), which is the silkworm homologue of mouse Fabp4 (aP2), a marker of adipocyte differentiation in mammals. BmFABP1 expression was increased by dexamethasone treatment. We also isolated the BmFABP1 promoter, and found that it was activated by a combination of drugs that included dexamethasone. The demonstration of dexamethasone-stimulated lipid accumulation and BmFABP1 expression in BmN4 cells provides a useful model of inducible adipogenesis. This system should be valuable for investigation of the molecular mechanisms of fat body formation, adipocyte differentiation, and lipid accumulation in the silkworm and other Lepidopteran insects.