20-hydroxyecdysone (20E) plays a role in the regulation of juvenile hormone synthesis in the mosquito Aedes aegypti

Juvenile hormone (JH) is an insect-specific sesquiterpenoid that regulates development and reproduction. In the yellow fever mosquito, Aedes aegypti, JH III is synthesized by a pair of endocrine glands with neural connections to the brain called the corpora allata (CA). JH titers are largely determined by the rate of biosynthetic activity of the CA which is tightly regulated by allatostatic (inhibitory) and allatotropic (stimulatory) factors. The ecdysteroid 20-hydroxyecdysone (20E) is a key regulator of insect development and reproduction which has been proposed as a modulator of JH synthesis in the lepidopteran Manduca sexta and Bombyx mori. In the present study, we evaluated in vitro the effect of 20E on JH synthesis in the pupal stage of the female mosquito.  Remarkably, 20E initiates JH biosynthesis in -24 h pupa at a time when the gland is inactive and transcript levels for most JH biosynthetic enzymes are low. Additionally, the application of 20E correlated with an increase in the enzymatic activity of juvenile hormone acid methyltransferase (JHAMT), a critical enzyme of the biosynthetic pathway. Moreover, incubation of isolated CA-CC revealed that the brain is required for the stimulation of JH synthesis by 20E in -24 h pupa.