Insect Nuclear Receptors

Abstract

The nuclear receptors (NRs) of metazoans are an ancient family of transcription factors defined by conserved DNA- and ligand-binding domains (DBDs and LBDs, respectively). The Drosophila melanogaster genome project revealed 18 canonical NRs (with DBDs and LBDs both present) and 3 receptors with the DBD only. Annotation of subsequently sequenced insect genomes revealed only minor deviations from this pattern. A renewed focus on functional analysis of the isoforms of insect NRs is therefore required to understand the diverse roles of these transcription factors in embryogenesis, metamorphosis, reproduction, and homeostasis. One insect NR, ecdysone receptor (EcR), functions as a receptor for the ecdysteroid molting hormones of insects. Researchers have developed nonsteroidal ecdysteroid agonists for EcR that disrupt molting and can be used as safe pesticides. An exciting new technology allows EcR to be used in chimeric, ligand-inducible gene-switch systems with applications in pest management and medicine.

20-hydroxyecdysone activates Forkhead box O to promote proteolysis during Helicoverpa armigera molting

“…20E binds to its nuclear receptor, ecdysone receptor (EcR), and forms a transcription complex with heterodimeric ultraspiracle protein (USP). The complex then binds to the ecdysone-response element (EcRE) to promote 20E-responsive gene transcription (Fahrbach et al, 2012;Riddiford et al, 2001). One of the 20E-response genes encodes the transcription factor Broad [Br, or Br-complex (Br-C)], which is crucial to initiate metamorphosis in the 20E pathway (Zhou and Riddiford, 2002).…”

BDE-47 causes developmental retardation with down-regulated expression profiles of ecdysteroid signaling pathway-involved nuclear receptor (NR) genes in the copepod Tigriopus japonicus

“…In early metamorphosis of the hemimetabolous insect (Blattella germanica), RNAi injection of EcR, USP, E75, HR3, and FTZ-F1 caused stage-specific developmental arrest (Cruz et al, 2008). To date, ecdysteroid signaling pathway-related genes have a role in both reproduction and development of ecdysozoa (Oro et al, 1992;Fahrbach et al, 2011). BDE-47 can alter endocrine secreting systems by disturbing internal secretion of ecdysteroid hormone, resulting in retardation of molting and metamorphosis in T. japonicus.…”

“…5). In Drosophila and insect mid-prepupal stage larvae, the FTZ-F1 gene was significantly expressed at low dose 20E exposure, while it was down-regulated with high-dose 20E (5 × 10 −6 M) (Beckstead et al, 2005;Fahrbach et al, 2011). In the honeybees Apis mellifera, a low level of 20E led to increased EcR gene expression during development, while high level 20E (5 g) repressed EcR expression (Mello et al, 2014).…”

Sequencing and structural homology modeling of the ecdysone receptor in two chrysopids used in biological control of pest insects

“…Ecdysteroids as the natural insect molting hormone 20-hydroxyecdysone (20E) bind to the ecdysone receptor (EcR) that is forming a functional heterodimer complex with the ultraspiracle protein (USP) and so plays an important role in regulating development and reproduction in insects and crustaceans (Nakagawa and Henrich 2009;Fahrbach et al 2012). The EcR is a member of the nuclear receptor superfamily, which comprises a group of receptors containing at least one of two highly conserved domains: the centrally located DNA binding domain (DBD) and the C-terminal ligand-binding domain (LBD) (Yao et al 1993;Billas et al 2009).…”