Cryptocephal, the Drosophila melanogaster ATF4, Is a Specific Coactivator for Ecdysone Receptor Isoform B2
(A) ETH transcript levels mirrored the changes in the circulating ecdysone titer with a 6.5 to 8 hr delay. Transcript levels were measured semi-quantitatively in as the intensity of ETH in situ hybridization in Inka cells in tracheal metamere 5 (TM5) and TM8 at five times at the onset of metamorphosis (relative to pupariation). The arrow indicates the peak of the late-larval pulse of circulating 20E, which occurs at pupariation . Means with the same lower case (TM5) or upper case (TM8) letters were not significantly different [p>0.05, n = 5–8; One-way ANOVA (TM5, p = 0.000776; TM8, p<0.000001) with Bonferroni (all-pairwise) multiple comparison test]. Insets below the histograms in (A) and (B) show representative images of cells at each time point. (B) The Inka cells of young third instar larvae fed with 20E for 12 hr showed higher expression levels for the fluorescent ETH reporter, ETH-EGFP (n = 4). *, p<0.05 (one-way ANOVA: TM5, p = 0.036; TM8, p = 0.044). Bar = 20 µM.