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Abstract
The reproductive cycle in female mosquitoes consists of alternating periods of rapid development and arrest. After a blood meal, ovary steroidogenesis, a key switch between arrest and egg development, is regulated by an insulin signaling cascade. The first step in this cascade is activation of the mosquito insulin receptor (MIR). After adult eclosion, from previtellogenesis until the end of vitellogenesis, MIR was observed on follicle cell membranes. During post-vitellogenesis, when follicle cells switch from steroid to chorion production, MIR was not expressed. Bovine insulin and an activator of the insulin receptor, pervanadate, both stimulated ovarian steroid production in vitro, and an inhibitor of the insulin receptor, HNMPA-(AM3), prevented steroid production. Furthermore, MIR became tyrosine phosphorylated when ovaries were stimulated with bovine insulin or pervanadate. Together, these data strongly suggest that MIR regulates steroidogenesis in the mosquito ovary.|A second signaling component, protein kinase B (PKB), was characterized in mosquito ovaries. The mosquito PKB gene, MPKB, encodes a 60 kDa protein containing a pleckstrin homology and catalytic domain. MPKB transcript was only found in early embryos and ovaries, with increased expression late in egg development. MPKB was detected in follicle cells prior to a bloodmeal, and was threonine phosphorylated after the ovaries were stimulated with insulin. Okidaic acid, an activator of PKB, stimulated ovary steroidogenesis in the absence of a steroidogenic hormone.|Phosphoinositide 3-kinase (PI3K), a third component of the insulin signaling cascade, acts between the insulin receptor and PKB. Partial sequences from two classes of PI3K were isolated from mosquito ovaries and share considerable sequence identity with PI3Ks from Drosophila. The catalytic subunit of a Class one PI3K in Ae. aegypti, named Aep110, contains catalytic, accessory, and C2 domains. Two inhibitors of PI3K, wortmannin and LY20094, prevented ovarian steroidogenesis in vitro. The Aep110 transcript was found in ovary, head, midgut, and body wall of adult females.