Cryptocephal, the Drosophila melanogaster ATF4, Is a Specific Coactivator for Ecdysone Receptor Isoform B2
(A) Ecdysis in third instar larvae expressing dominant negative EcR-B1-F645A only in the Inka cells (n = 98; EcR-B1 DN) was rescued by expression of EcR-B2 (n = 165) or EcR-B2-E9K (n = 143), but not by expression of EcR-B1 (n = 91) or EcR-A (n = 59). The controls had ETH-GSW only (n = 148), and all larvae were fed RU486. The larval counts included all live third instar larvae (with or without multiple mouthparts), as well as all dead larvae (of all stages). All of the dead larvae found had multiple mouthparts. (B) ETH expression in Inka cells expressing dominant negative EcR-B1-F645A isoform (n = 11) was rescued by co-expression of wild-type EcR-B2 (n = 8) but not wild-type EcR-B1 (n = 9) or the E9K mutant of EcR-B2 (n = 8). The controls had ETH-GSW only (n = 8), and all larvae were fed RU486. All larvae were dissected at ∼12 hr after ecdysis to the third instar. Means with the same lower case (TM5) or upper case (TM8) letters were not significantly different [p>0.05, One-way ANOVA (TM5, p<0.000001; TM8, p = 0.000002) with Bonferroni (all-pairwise) multiple comparison test].