20-hydroxyecdysone stimulation of juvenile hormone biosynthesis by the mosquito corpora allata

Aug 11, 2015Insect biochemistry and molecular biology

How 20-Hydroxyecdysone increases juvenile hormone production in the mosquito hormone gland

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Abstract

Stimulation with 20-hydroxyecdysone (20E) led to a remarkable increase in juvenile hormone (JH) biosynthesis in mosquito pupae.

20E functions as an age-linked hormonal signal, activating the corpora allata in mosquito pupae.
In vitro stimulation of the brain-corpora allata-corpora cardiaca complex with 20E increased JH production and the activity of juvenile hormone acid methyltransferase.
Methyl farnesoate stimulated JH synthesis, indicating the presence of epoxidase activity in the pupae, while farnesoic acid did not.
Separation of the corpora allata-corpora cardiaca complex from the brain in early pupae activated JH synthesis.
An increase in 20E levels may counteract the brain's inhibitory effect on JH synthesis, mimicking the effects of denervation.

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Juvenile hormone III (JH) is synthesized by the corpora allata (CA) and plays a key role in mosquito development and reproduction. JH titer decreases in the last instar larvae allowing pupation and metamorphosis to progress. As the anti-metamorphic role of JH comes to an end, the CA of the late pupa (or pharate adult) becomes again "competent" to synthesize JH, which plays an essential role orchestrating reproductive maturation. 20-hydroxyecdysone (20E) prepares the pupae for ecdysis, and would be an ideal candidate to direct a developmental program in the CA of the pharate adult mosquito. In this study, we provide evidence that 20E acts as an age-linked hormonal signal, directing CA activation in the mosquito pupae. Stimulation of the inactive brain-corpora allata-corpora cardiaca complex (Br-CA-CC) of the early pupa (24 h before adult eclosion or -24 h) in vitro with 20E resulted in a remarkable increase in JH biosynthesis, as well as increase in the activity of juvenile hormone acid methyltransferase (JHAMT). Addition of methyl farnesoate but not farnesoic acid also stimulated JH synthesis by the Br-CA-CC of the -24 h pupae, proving that epoxidase activity is present, but not JHAMT activity. Separation of the CA-CC complex from the brain (denervation) in the -24 h pupae also activated JH synthesis. Our results suggest that an increase in 20E titer might override an inhibitory effect of the brain on JH synthesis, phenocopying denervation. All together these findings provide compelling evidence that 20E acts as a developmental signal that ensures proper reactivation of JH synthesis in the mosquito pupae.

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20-hydroxyecdysone stimulation of juvenile hormone biosynthesis by the mosquito corpora allata

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