Effect of insulin and 20-hydroxyecdysone in the fat body of the yellow fever mosquito, Aedes aegypti

In mosquitoes, yolk protein precursor (YPP) gene expression is activated after a blood meal through the synergistic action of a steroid hormone and the amino acid/target of rapamycin (TOR) signaling pathway in the fat body. We investigated the role of insulin signaling in the regulation of YPP gene expression. The presence of mosquito insulin receptor (InR) and the Protein kinase B (PKB/Akt) in the adult fat body of female mosquitoes was confirmed by means of the RNA interference (RNAi). Fat bodies stimulated with insulin were able to promote the phosphorylation of ribosomal S6 Kinase, a key protein of the TOR signaling pathway. Importantly, insulin in combination with 20-hydroxyecdysone activated transcription of the YPP gene vitellogenin (Vg), and this process was sensitive to the phosphoinositide-3 kinase (PI-3k) inhibitor LY294002 as well as the TOR inhibitor rapamycin. RNAi-mediated knockdown of the mosquito InR, Akt, and TOR inhibited insulin-induced Vg gene expression as well as S6 Kinase phosphorylation in in vitro fat body culture assays.