Insulin receptor expression during development and a reproductive cycle in the ovary of the mosquito Aedes aegypti
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A key tyrosine kinase receptor regulates steroidogenesis during egg maturation in the mosquito Aedes aegypti. This study examined expression patterns and phosphorylation states of the mosquito insulin receptor (MIR) in ovaries during the previtellogenic stage and a reproductive cycle. Little or no MIR protein was present until 24 h after adult eclosion, when the mature MIR appeared as a ~400-kDa tetrameric protein composed of two 116-kDa α-subunits and two 95-kDa β-subunits. Immunocytochemistry showed that MIR was localized in the cell membranes of follicle cells surrounding the oocyte and nurse cells. Protein and mRNA transcript levels gradually increased in ovaries during the first few days after eclosion, and remained constant during previtellogenic arrest for up to 21 days. During a reproductive cycle, MIR protein levels remained constant up to 12 h post-bloodmeal (pbm). However, from 24 to 48 h pbm, during chorion deposition, the MIR protein was not detected. By 72 h pbm, after oviposition, the level of MIR protein returned to pre-bloodmeal levels. Two peaks of MIR transcript occurred in ovaries after a bloodmeal, immediately following a bloodmeal and after oviposition. MIR protein was constitutively phosphorylated on tyrosine residues at low levels during the previtellogenic arrest stage. Tyrosine phosphorylation increased three- to fourfold when ovaries were incubated with bovine insulin in vitro, and twofold when incubated with sodium orthovanadate, thus demonstrating a role for MIR in activating steroidogenesis. Notably, MIR protein and transcript were not detected in eggs, larvae, pupae, or pharate adults.
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