Functions of the ecdysone receptor isoform-A in the hemimetabolous insect Blattella germanica revealed by systemic RNAi in vivo.

The molecular basis of ecdysteroid function during development has been analyzed in detail in holometabolous insects, especially in Drosophila melanogaster, but rarely in hemimetabolous. Using the hemimetabolous species Blattella germanica (German cockroach) as model, we show that the ecdysone receptor isoform-A (BgEcR-A) mRNA is present throughout the penultimate and last nymphal instars in all tissues analyzed (prothoracic gland, epidermis and fat body). To study the functions of BgEcR-A, we reduced its expression using systemic RNAi in vivo, and we obtained knockdown specimens. Examination of these specimens indicated that BgEcR-A during the last nymphal instar is required for nymphal survival, and that reduced expression is associated with molting defects, lower circulating ecdysteroid levels and defects in cell proliferation in the follicular epithelium. Some BgEcR-A knockdown nymphs survive to the adult stage. The features of these specimens indicate that BgEcR-A is required for adult-specific developmental processes, such as wing development, prothoracic gland degeneration and normal choriogenesis.