E74A protein is sufficient to inhibit its own ecdysone-induced transcription.

<p>(A) Experimental paradigm for expressing E74A protein prior to the prepupal pulse of ecdysone. Expression profile of endogenous <i>E74A</i> mRNA (in gray) and E74A protein (in blue) in salivary glands shown relative to hours after head eversion (AHE). Arrows mark timing of the 30 minute heat-shock treatment and the subsequent dissection of larval salivary glands. (B) Precocious expression of E74A protein (gray bars) is sufficient to repress induction of endogenous <i>E74A</i> mRNA in control and <i>bel^psg9</i> mutant salivary glands. Control salivary glands show over 100-fold induction of <i>E74A</i> in response to the prepupal pulse of ecdysone (first bar from left). In contrast, ectopic expression of E74A protein (second bar), but not E75A protein (third bar), inhibits endogenous <i>E74A</i> transcription. Similarly, ectopic E74A protein inhibits the ecdysone-induced expression of <i>E74A</i> in <i>bel^psg9</i> mutant salivary glands (fourth and fifth bars). (C) Although precocious expression of E74A protein is sufficient to repress the ecdysone-induced transcription of <i>E74A</i>, it has a minor effect on the expression of ecdysone early response genes <i>E75A</i> and <i>BR-C Z1</i>. Salivary glands dissected from heat-shock-treated control (white bars) and <i>hs-E74A</i> carrying (gray bars) animals. (D) <i>E74A</i> is not necessary for the regression of other ecdysone early response genes. Salivary glands dissected from control (white bars) and <i>E74A^neo24/Df</i> mutant (gray bars) animals at +1.5 AHE, when endogenous expression of early response genes <i>E75A</i> and <i>BR-C</i> have regressed to levels prior to the ecdysone pulse. <i>E74A^neo24</i> allele is an RNA null, hence the barely detectable levels of endogenous <i>E74A</i> mRNA. y-axis plots relative expression, normalized to <i>rp49</i>. Expression ratios in 5B calculated relative to −4 AHE control samples to show induction in response to the prepupal pulse of ecdysone. All samples are in triplicate; asterisks indicate p-values <0.05. <i>bel/Df</i>: <i>bel^psg9/Df</i>. AHE: after head eversion.