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First published online 10 June 2009
doi: 10.1242/dev.032672

Development 136, 2345-2353 (2009)
Published by The Company of Biologists 2009
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The Ecdysone receptor controls the post-critical weight switch to nutrition-independent differentiation in Drosophila wing imaginal discs

Christen K. Mirth1,2,*, James W. Truman2 and Lynn M. Riddiford1,2

1 Department of Biology, Box 351800, University of Washington, Seattle, WA 98195, USA.
2 Janelia Farm, HHMI, 19700 Helix Drive, Ashburn, VA 20147, USA.

* Author for correspondence (e-mail: mirthc{at}janelia.hhmi.org)

Accepted 29 April 2009

In holometabolous insects, a species-specific size, known as critical weight, needs to be reached for metamorphosis to be initiated in the absence of further nutritional input. Previously, we found that reaching critical weight depends on the insulin-dependent growth of the prothoracic glands (PGs) in Drosophila larvae. Because the PGs produce the molting hormone ecdysone, we hypothesized that ecdysone signaling switches the larva to a nutrition-independent mode of development post-critical weight. Wing discs from pre-critical weight larvae [5 hours after third instar ecdysis (AL3E)] fed on sucrose alone showed suppressed Wingless (WG), Cut (CT) and Senseless (SENS) expression. Post-critical weight, a sucrose-only diet no longer suppressed the expression of these proteins. Feeding larvae that exhibit enhanced insulin signaling in their PGs at 5 hours AL3E on sucrose alone produced wing discs with precocious WG, CT and SENS expression. In addition, knocking down the Ecdysone receptor (EcR) selectively in the discs also promoted premature WG, CUT and SENS expression in the wing discs of sucrose-fed pre-critical weight larvae. EcR is involved in gene activation when ecdysone is present, and gene repression in its absence. Thus, knocking down EcR derepresses genes that are normally repressed by unliganded EcR, thereby allowing wing patterning to progress. In addition, knocking down EcR in the wing discs caused precocious expression of the ecdysone-responsive gene broad. These results suggest that post-critical weight, EcR signaling switches wing discs to a nutrition-independent mode of development via derepression.

Key words: Ecdysone receptor, Critical weight, Size control, Wing imaginal disc patterning, Drosophila


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Ecdysone uncouples wing development from nutrition

Development 2009 136: e1402. [Full Text]  





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