The ecdysis triggering hormone system is essential for successful moulting of a major hemimetabolous pest insect, Schistocerca gregaria

Cynthia Lenaerts,Dorien Cools,Rik Verdonck,Elisabeth Marchal,Lina Verbakel,Jozef Vanden Broeck

doi:10.1038/srep46502

Abstract

Insects are enclosed in a rigid exoskeleton, providing protection from desiccation and mechanical injury. To allow growth, this armour needs to be replaced regularly in a process called moulting. Moulting entails the production of a new exoskeleton and shedding of the old one and is induced by a pulse in ecdysteroids, which activates a peptide-mediated signalling cascade. In Holometabola, ecdysis triggering hormone (ETH) is the key factor in this cascade. Very little functional information is available in Hemimetabola, which display a different kind of development characterized by gradual changes. This paper reports on the identification of the ETH precursor and the pharmacological and functional characterisation of the ETH receptor in a hemimetabolous pest species, the desert locust, Schistocerca gregaria. Activation of SchgrETHR by SchgrETH results in an increase of both Ca2+ and cyclic AMP, suggesting that SchgrETHR displays dual coupling properties in an in vitro cell-based assay. Using qRT-PCR, an in-depth profiling study of SchgrETH and SchgrETHR transcripts was performed. Silencing of SchgrETH and SchgrETHR resulted in lethality at the expected time of ecdysis, thereby showing their crucial role in moulting.

Highlights

Insects are enclosed in a rigid exoskeleton, providing protection from desiccation and mechanical injury
Via a positive feedback loop between eclosion hormone (EH) and ecdysis triggering hormone (ETH) there is a massive release of both peptides in the hemolymph, which leads to the activation of the neuronal network producing cyclic GMP, crustacean cardioactive peptide (CCAP), bursicon and other neuropeptides which control ecdysis and post-ecdysis behavioural sequences
The open reading frames (ORF) of the SchgrETHR consists of 1323 nucleotides encoding a 441 amino acid-long receptor 1(Supplementary Fig. S1)

Summary

Introduction

Insects are enclosed in a rigid exoskeleton, providing protection from desiccation and mechanical injury To allow growth, this armour needs to be replaced regularly in a process called moulting. While JHs determine the nature of the moult, ecdysteroids trigger the moulting process and activate a neuropeptide signalling cascade which in turn regulates the ecdysis sequence at the end of the moulting cycle. In M. sexta, increasing concentrations of ecdysteroids result in production of ecdysis triggering hormone (ETH) in Inka cells attached to the trachea. When ecdysteroid titres decline again, ETH is secreted and activates neurons producing kinins and Corticotropin Releasing Factor (CRF)-like diuretic hormones (DHs), which trigger the pre-ecdysis behaviour sequence. Silencing of ETH or ETHR in different Holometabola resulted in lethality at the expected time of ecdysis[4,5,8,15,20]

Methods

Results

Discussion

Conclusion