Indirect control of yolk protein genes by 20-hydroxyecdysone in the fat body of the mosquito, Aedes aegypti
In response to a blood meal, the fat body of the female mosquito, Aedes aegypti, begins massive production of several yolk proteins which are subsequently stored in the developing oocytes. Although 20-hydroxyecdysone (20E) is important for initiation and maintenance of expression of the yolk protein genes encoding vitellogenin (Vg) and vitellogenic carboxypeptidase (VCP), the exact nature of 20E action has not been clearly defined. A primary question is whether this hormone directly stimulates expression of the genes for Vg and VCP or if it acts indirectly through a hormone response cascade. We have demonstrated that 10(-4) M cycloheximide (Chx) reversibly inhibits > 98% of protein synthesis in in vitro fat body culture. 10(-5) M 20E stimulates high levels of the mRNAs for Vg and VCP in previtellogenic fat bodies cultured in vitro, but initiation of this expression is eliminated by Chx. Thus, our results indicate that protein synthesis is required in response to 20E before increased levels of yolk protein mRNAs can be measured. We therefore conclude that the action of 20E is indirect.