Abstract:  In insects, ecdysone signal transduction pathway is mediated by a cascade of transcription factors, and ecdysone receptor (EcR), Broad complex (BR-C) and E74A are believed to be the early response factors. To study the functions of these early transcription factors in Lepidoptera, double-stranded RNAs (dsRNAs) of these genes of Bombyx mori were synthesized in vitro and injected into the wandering larvae. Phenotype changes were observed and the expression of these and related genes were analyzed by quantitative real-time PCR (qPCR). Asynchronous pupation and eclosion, deviant wing and death of pupae and moths were observed after interference of BmEcR, BmBR-C and BmE74A. The qPCR results revealed that partial silence of BmEcR decreased the mRNA levels of BmE74A, BmE74B, BmHR3A and BmβFTZ-F1. Partial silence of BmE74A reduced the mRNA levels of BmEcR, BmBR-C, BmE74B, BmHR3A and BmβFTZ-F1, while partial silence of BmBR-C resulted in a significant decrease in the expression levels of all tested genes except for BmIAP. These results implied that BmBR-C may act at the earlier stage in ecdysone signal pathway and regulate the expression of other transcription factor genes as well as ecdysone receptor gene BmEcR in the silkworm.

Key words: Bombyx mori, RNA interference, metamorphosis, ecdysone, transcription factor