Ovarian follicle cells are the source of ecdysone in the ovaries of Aedes aegypti mosquitoes

The mosquito Aedes aegypti serves as a model for insect ovarian steroidogenesis, and understanding this process may provide additional targets for controlling vector populations. After a female mosquito takes a blood meal, neuropeptides released from the brain stimulate the ovaries to produce the steroid hormone ecdysone for up to 30 hours. Cholesterol is the initial substrate for ecdysone synthesis, but its movement and localization in the context of ovarian ecdysteroidogenesis is unknown. Previous work on other insects has shown that the follicle cells around each oocyte are the source of ecdysone, but recent work suggests the nurse cells are the source in the ovaries of Drosophila. Filipin staining indicates that the ovaries in non-blood fed mosquitoes are a free cholesterol repository. Within the ovaries, much of the cholesterol staining resides in the plasma membrane of the follicle cells. Additionally, immunostaining of the Halloween gene proteins involved in the initial ecdysone synthesis steps localized to the follicle cells. No difference in staining was observed between ovaries from blood fed mosquitoes and ovaries from non-blood fed mosquitoes. Taken together, these results indicate that the follicle cells possess both the resources and machinery necessary for ovarian ecdysone biosynthesis.