Regulation of the ecdysone receptor, USP, E75 and MHR3 mRNAs by 20‐hydroxyecdysone in the GV1 cell line of the tobacco hornworm,Manduca sexta

The responsiveness of several nuclear transcription factor genes to 20-hydroxyecdysone (20E) was characterized in an embryonic cell line, GV1, fromManduca sexta. The mRNA for theManducaecdysone receptor (MsEcR) was present in the GV1 cells and transiently increased 2.3-fold by 5 h after the addition of 2 μg/ml (4 × 10−6M) 20-hydroxyecdysone (20E). In contrast,Manducaultraspiracle (MsUSP) mRNA level in the GV1 cells decreased slowly to half of its initial level by 12 h when exposed to the same concentration of 20E. The mRNAs for two putative transcription factors,MsE75 and MHR3, were induced in the GV1 cells by 20E, with that for E75 appearing within 1 h whereas that for MHR3 within 2 h. The ED50s for induction ofMsE75andMHR3gene expression in GV1 cells were 1.2 × 10−6 and 2.5 × 10−6M20E, respectively.