Abstract
Background20-hydroxyecdysone (20E) and its receptor complex ecdysone receptor (EcR) and ultraspiracle (USP) play a crucial role in controlling development, metamorphosis, reproduction and diapause. The ligand-receptor complex 20E-EcR/USP directly activates a small set of early-response genes and a much larger set of late-response genes. However, ecdysone-responsive genes have not been previously characterized in the context of insect chitin biosynthesis.Principal FindingsHere, we show that injection-based RNA interference (RNAi) directed towards a common region of the two isoforms of SeEcR in a lepidopteron insect Spodoptera exigua was effective, with phenotypes including a high mortality prior to pupation and developmental defects. After gene specific RNAi, chitin contents in the cuticle of an abnormal larva significantly decreased. The expression levels of five genes in the chitin biosynthesis pathway, SeTre-1, SeG6PI, SeUAP, SeCHSA and SeCHSB, were significantly reduced, while there was no difference in the expression of SeTre-2 prior to 72 hr after injection of EcR dsRNA. Meanwhile, injection of 20E in vivo induced the expression of the five genes mentioned above. Moreover, the SeTre-1, SeG6PI, SeUAP and SeCHSB genes showed late responses to the hormone and the induction of SeTre-1, SeG6PI, SeUAP and SeCHSB genes by 20E were able to be inhibited by the protein synthesis inhibitor cycloheximide in vitro indicating these genes are 20E late-response genes.ConclusionsWe conclude that SeTre-1, SeG6PI, SeUAP and SeCHSB in the chitin biosynthesis pathway are 20E late-response genes and 20E and its specific receptors plays a key role in the regulation of chitin biosynthesis via inducing their expression.
Highlights
We conclude that SeTre-1, SeG6PI, SeUAP and SeCHSB in the chitin biosynthesis pathway are 20E late-response genes and 20E and its specific receptors plays a key role in the regulation of chitin biosynthesis via inducing their expression
Throughout the insect life cycle, the steroid hormone 20hydroxyecdysone (20E) coordinates multiple developmental events by eliciting a complex genetic program via a heterodimeric nuclear receptor composed of the ecdysone receptor (EcR) and ultraspiracle proteins (USP)
Evidenced in a study of fruit fly Drosophila melanogaster by Ashburner et al first revealed that a part of this developmental program consists of a genetic cascade in which the ligand-receptor complex 20E-EcR/USP directly activates the expression of a very small number of early-response genes
Summary
Throughout the insect life cycle, the steroid hormone 20hydroxyecdysone (20E) coordinates multiple developmental events by eliciting a complex genetic program via a heterodimeric nuclear receptor composed of the ecdysone receptor (EcR) and ultraspiracle proteins (USP). Evidenced in a study of fruit fly Drosophila melanogaster by Ashburner et al first revealed that a part of this developmental program consists of a genetic cascade in which the ligand-receptor complex 20E-EcR/USP directly activates the expression of a very small number of early-response genes. The EcR, USP and a large number of ecdysone-responsive genes from the two gene categories proposed in the Ashburner model have been characterized in D. melanogaster and several other insect species [4,5,6] All of those studies published over the past decade have provided powerful evidence in support of the Ashburner model, meantime taken beyond that model which presented us with diverting new directions for our understanding of ecdysone signaling [7,8,9,10]. Most of the studies regarding the ecdysone-responsive genes in insects have focused on the regulatory genes at the top of the ecdysone-elicit genetic hierarchy
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