Expression of ecdysteroid-regulated transcripts in the silk gland of the wax moth, Galleria mellonella

Expression of six different transcripts encoding members of the nuclear receptor superfamily was studied in whole silk glands of the wax moth, Galleria mellonella, during development and in response to 20-hydroxyecdysone (20E) and juvenile hormone (JH II) in vitro. Nucleic acid probes specific to Galleria homologs of the Drosophila E75 early gene and the delayed early gene DHR3 were used to follow mRNAs encoding isoforms A and B of the E75 protein and GHR3 protein, respectively. Among these mRNAs, E75A mRNA appeared first during the larval molt and was most rapidly induced by 20E, while E75B and GHR3 mRNAs appeared with a 2 h delay. Unlike E75B mRNA, GHR3 mRNA required protein synthesis for its full induction. The 20E-induced levels of E75A mRNA were increased one and a half-fold within 1 h in the presence of 10-100 ng/ml JH II in cultured silk glands. Antisense cRNA probes for the Manduca sexta ecdysone receptor isoforms EcR-A and EcR-B1 detected transcripts that were directly induced by 20E in cultured silk glands. The levels of the putative EcR-A mRNA were high relative to those of EcR-B1 mRNA in silk glands at molting and metamorphosis. An antisense cRNA probe for the Man duca Ultraspiracle homolog detected a 4 kb mRNA that was most abundant around the time of larval ecdysis but was not induced by 20E in vitro.