Ecdysis triggering hormone ensures proper timing of juvenile hormone biosynthesis in pharate adult mosquitoes

Sep 27, 2014Insect biochemistry and molecular biology

Ecdysis triggering hormone helps control the timing of juvenile hormone production in developing adult mosquitoes

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Abstract

Ecdysis triggering hormone (ETH) regulates juvenile hormone (JH) synthesis in pharate adult mosquitoes.

A decrease in JH levels allows for pupation and metamorphosis in larvae.
ETH receptors are present in the corpora allata and peak in expression 4 hours before eclosion.
In vitro stimulation with ETH increases JH synthesis in pupal corpora allata.
Silencing ETH receptors in pupae reduces JH synthesis in one-day-old adult females.
ETH stimulation enhances the activity of juvenile hormone acid methyltransferase, an enzyme crucial for JH production.
Blocking calcium release from the endoplasmic reticulum inhibits ETH-driven increases in JH biosynthesis.

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Juvenile hormones (JHs) are synthesized by the corpora allata (CA) and play a key role in insect development. A decrease of JH titer in the last instar larvae allows pupation and metamorphosis to proceed. 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 would play an essential role orchestrating reproductive maturation. In the present study, we provide evidence that ecdysis triggering hormone (ETH), a key endocrine factor involved in ecdysis control, acts as an allatotropic regulator of JH biosynthesis, controlling the exact timing of CA activation in the pharate adult mosquito. Analysis of the expression of Aedes aegypti ETH receptors (AeaETHRs) revealed that they are present in the CA and the corpora cardiaca (CC), and their expression peaks 4 h before eclosion. In vitro stimulation of the pupal CA glands with ETH resulted in an increase in JH synthesis. Consistent with this finding, silencing AeaETHRs by RNA interference (RNAi) in pupa resulted in reduced JH synthesis by the CA of one day-old adult females. Stimulation with ETH resulted in increases in the activity of juvenile hormone acid methyltransferase (JHAMT), a key JH biosynthetic enzyme. Furthermore, inhibition of IP3R-operated mobilization of endoplasmic reticulum Ca(2+) stores prevented the ETH-dependent increases of JH biosynthesis and JHAMT activity. All together these findings provide compelling evidence that ETH acts as a regulatory peptide that ensures proper developmental timing of JH synthesis in pharate adult mosquitoes.

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Ecdysis triggering hormone ensures proper timing of juvenile hormone biosynthesis in pharate adult mosquitoes

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