Spatial patterns of XXXX activation during the onset of Drosophila metamorphosis.

@entity51131 @entity59304 @entity11088
Ecdysteroid signaling in insects is transduced by a heterodimer of the @entity51131 and @entity59304 nuclear receptors. In order to monitor the temporal and spatial patterns of ecdysteroid signaling in vivo we established transgenic animals that express a fusion of the GAL4 DNA binding domain and the ligand binding domain (LBD) of @entity51131 or @entity59304 , combined with a GAL4-dependent lacZ reporter gene. The patterns of beta-galactosidase expression in these animals indicate where and when the GAL4-LBD fusion protein has been activated by its ligand in vivo. We show that the patterns of GAL4- @entity51131 and GAL4- @entity59304 activation at the onset of metamorphosis reflect what would be predicted for ecdysteroid activation of the @entity51131 / @entity59304 heterodimer. No activation is seen in mid-third instar larvae when the ecdysteroid titer is low, and strong widespread activation is observed at the end of the instar when the ecdysteroid titer is high. In addition, both GAL4- @entity51131 and GAL4- @entity59304 are activated in larval organs cultured with @entity11088 (20E), consistent with @entity51131 / @entity59304 acting as a 20E receptor. We also show that GAL4- @entity59304 activation depends on @entity51131 , suggesting that @entity59304 requires its heterodimer partner to function as an activator in vivo. Interestingly, we observe no GAL4-LBD activation in the imaginal discs and ring glands of late third instar larvae. Addition of 20E to cultured mid-third instar imaginal discs results in GAL4- @entity59304 activation, but this response is not seen in imaginal discs cultured from late third instar larvae, suggesting that @entity51131 / @entity59304 loses its ability to function as an efficient activator in this tissue. We conclude that @entity51131 / @entity59304 activation by the systemic ecdysteroid signal may be spatially restricted in vivo. Finally, we show that GAL4- @entity51131 functions as a potent and specific dominant negative at the onset of metamorphosis, providing a new tool for characterizing ecdysteroid signaling pathways during development.
