Ecdysteroid signalling components in metamorphosis and development of the desert locust, Schistocerca gregaria

Abstract

The arthropod-specific hormone family of ecdysteroids plays an important role in regulating diverse physiological processes, such as moulting and metamorphosis, reproduction, diapause and innate immunity. Ecdysteroids mediate their response by binding to a heterodimeric complex of two nuclear receptors, the ecdysone receptor (EcR) and the retinoid-X-receptor/ultraspiracle (RXR/USP). In this study we investigated the role of EcR and RXR in metamorphosis and development of the desert locust, Schistocerca gregaria. The desert locust is a voracious, phytophagous, swarming pest that can ruin crops and harvests in some of the world's poorest countries. A profound knowledge of the ecdysteroid signalling pathway can be used in the development of more target-specific insecticides to combat this harmful plague insect. Here we report an in-depth profiling study of the transcript levels of EcR and RXR, as well as its downstream response genes, in different tissues isolated throughout the last larval stage of a hemimetabolous insect, showing a clear correlation with circulating ecdysteroid titres. Using RNA interference (RNAi), the role of SgEcR/SgRXR in moulting and development was investigated. We have proven the importance of the receptor components for successful moulting of locust nymphs into the adult stage. Some SgEcR/SgRXR knockdown females were arrested in the last larval stage, and 65 % of them initiated vitellogenesis and oocyte maturation, which normally only occurs in adults. Furthermore, our results clearly indicate that at the peak of ecdysteroid synthesis, on day six of the last larval stage, knockdown of SgEcR/SgRXR is affecting the transcript levels of the Halloween genes, Spook, Shadow and Shade.

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

“…After a boost injection (200 ng) on day 3, the locusts were sacrificed on day 6 to check the effect of RNAi-mediated knockdown of SchgrEcR / SchgrRXR on the transcript levels of SchgrETHR and SchgrETHpre. The knockdown efficiency of this experiment was previously published in Lenaerts et al ,29. SchgrETHR and SchgrETHpre transcript levels were respectively 52% and 78% lower in the epidermis of SchgrEcR/SchgrRXR knockdown animals when compared to control animals (Fig.…”

“…Forward and reverse primers flanked by the T7 promoter sequence were (Table 3) used in a PCR reaction with REDTaq ® DNA polymerase (Sigma-Aldrich Co.) to amplify a fragment of the target gene (200–600 bp). Both dsRNA constructs for SchgrEcR as well as SchgrRXR were designed against the common region of their isoforms29. PCR products were analysed using horizontal agarose gel electrophoresis and visualized using UV.…”

“…6. To investigate the effect of an RNAi-mediated knockdown of the ecdysone receptor complex, SchgrEcR/SchgrRXR , on the transcript levels of SchgrETHR and SchgrETHpre , we used samples from an earlier published experiment29. There newly moulted fifth instars were injected with a mix of SchgrEcR and SchgrRXR dsRNA construct (200 ng each in 8 μL locust Ringer solution).…”

Functional characterization of ultraspiracle in Leptinotarsa decemlineata using RNA interference assay

“…In agreement with our results, loss of maternal or zygotic USP functions in D. melanogaster lead to embryonic lethality (Henrich et al , ; Ghbeish et al , ), or death at the first larval moult (Oro et al , ). Moreover, knockdown of USP causes larval lethality during the quiescent stage in T. castaneum (Tan and Palli, ), impairs pupation and adult emergence in G. molesta (Cao et al , ) and results in moulting failure in B. germanica (Martin et al , ) and S. gregaria (Lenaerts et al , ).…”

Performance of reproductive system of Dichelops melacanthus (Hemiptera: Pentatomidae) subjected to buprofezin and pyriproxyfen: morphological analysis of ovarioles and testes

“…It is known that JH acts in lipid synthesis (ZIBAEE et al, 2011), which is important for formation of adult females, mainly for the production of vitellogenin (GUO et al, 2014;SMYKAL et al, 2014). Ecdysone is an important agent for the ecdysis of insects; in addition to controlling the biosynthesis of chitin, diapause and the immune system (LENAERTS et al, 2016), this hormone is also involved in the development of ovarian structure (ZERA; BOTTSFORD, 2001). …”