Nuclear receptor HR4 plays an essential role in the ecdysteroid-triggered gene cascade in the development of the hemimetabolous insect Blattella germanica

Despite the differences in the developmental strategies between hemimetabolous and holometabolous insects, a common feature between both types of development is that periodic pulses of the steroid hormone 20-hydroxyecdysone (20E) dictate each developmental transition. Although the molecular action of 20E has been extensively studied in holometabolous insects, data on hemimetabolous is scarce. To address this, we have used the German cockroach Blattella germanica to show that 20E signals through a transcriptional cascade of the nuclear hormone receptor-encoding genes BgE75, BgHR3 and BgFTZ-F1. Here, we report the isolation and functional characterization of BgHR4, another nuclear receptor involved in this cascade. Expression studies along with tissue incubations and RNAi experiments show that cross-regulation between BgE75 and BgHR3 directs the expression of BgHR4. Finally, we have also shown that BgHR4 is an essential gene required for successfully completing nymphal–nymphal and nymphal–adult transitions, by allowing the appropriate delay in the induction of BgFTZ-F1.

► Nuclear receptor HR4 is a vital gene in the development of the hemimetabolan insect Blattella germanica. ► Cross-regulation among nuclear receptors E75 and HR3 directs the expression of HR4. ► HR4 plays a key role in repressing 20-hydroxyecdysone-regulated gene expression. ► BgHR4 is necessary for the activation of the key nuclear receptor BgFTZ-F1.