Ecdysone receptor (EcR) suppresses lipid accumulation in the Drosophila fat body via transcription control

Abstract

Lipid metabolism drastically changes in response to the environmental factors in metazoans. Lipid is accumulated at the food rich condition, while mobilized in adipocyte tissue in starvation. Such lipid mobilization is also evident during the pupation of the insects. Pupation is induced by metamorphosis hormone, ecdysone via ecdysone receptor (EcR) with lipid mobilization, however, the molecular link of the EcR-mediated signal to the lipid mobilization remains elusive. To address this issue, EcR was genetically knocked-down selectively in 3rd instar larva fat body of Drosophila, corresponding to the adipocyte tissues in mammalians, that contains adipocyte-like cells. In this mutant, lipid accumulation was increased in the fat body. Lipid accumulation was also increased when knocked-down of taiman, which served as the EcR co-activator. Two lipid metabolism regulatory factor, E75B and adipose (adp) as well as cell growth factor, dMyc, were found as EcR target genes in the adipocyte-like cells, and consistently knock-down of these EcR target genes brought phenotypes in lipid accumulation supporting EcR function. These findings suggest that EcR-mediated ecdysone signal is significant in lipid metabolism in insects.