Local ecdysone synthesis in a wounded epithelium sustains developmental delay and promotes regeneration in Drosophila Restricted; Files Only
Terry, Douglas (Summer 2023)
Abstract
The capacity for regeneration is often lost as animals mature past embryonic or juvenile stages, suggesting a dependence on redirecting developmental signals away from patterned growth and toward localized regenerative growth. This generally corresponds with a pause in growth of uninjured tissues that avoids developmental asynchrony by allowing the injured tissue to repair before rejoining a normal developmental trajectory. Yet, how local and systemic endocrine signaling are coordinated to promote tissue regeneration while stalling systemic developmental growth remains poorly understood.
Loss of regeneration competence in a commonly used Drosophila wing injury system parallels the rapid rise in levels of the steroid hormone ecdysone (Ec) that peaks at the larval-to-pupal transition. This apparently inverse relationship has led to the hypothesis that high level Ec inhibits wing regeneration. However, low level Ec is present throughout regeneration-competent larval stages, and Ec has been shown to promote cell proliferation and tissue growth. Moreover, low level Ec and its receptor EcR are required for activity of the pro-growth Dpp and Wg pathways, which promote normal and regenerative wing disc growth.
The apparent paradox that injury results in systemic depletion of the Ec larval growth hormone at a time when the wing blastema is undergoing regenerative growth led us to assess Ec roles and activity within injured wing discs. We find that as EcR activity drops elsewhere in the disc, it rises in the blastema region. In parallel, local depletion of Ec biosynthesis enzymes consistently impairs regrowth of injured wings, while local depletion of the Ec catabolic enzyme Cyp18a1 enhances regeneration. We trace these effects to a requirement for Ec in both injury-induced developmental delay and coordinated growth reduction and find that expression of mRNAs encoding the key regeneration regulators Ets21C and Upd3 expression are responsive to Ec produced locally at the site of injury. These findings suggest that 20E promotes elements of the regenerative transcriptional program in the wing disc, and that the blastema is a unique signaling environment that generates its own Ec to sustain a tissue repair program. Thus, the studies described in this dissertation provide a novel addition to our understanding of how local and systemic Ec production are coordinated to create a privileged transcriptional environment to support tissue repair that may provide insight into regulation of endocrine signaling molecules during tissue regeneration in diverse species.
Table of Contents
Chapter 1. Introduction 1
1.1 Regeneration as a scientific field of study 1
1.2 Comparative study of regeneration 3
1.3 Features of Drosophila as a model organism to understand regeneration 7
1.3.1 Strengths of Drosophila as a model system 7
1.3.2 Regenerative capacity of Drosophila 8
1.3.3 Imaginal wing disc development and patterning 10
1.4 Drosophila imaginal disc regeneration 13
1.4.1 Injury models 13
1.4.2 Wing disc regeneration blastema 16
1.4.3 Organismal aspects of regeneration 19
1.5 Ecdysteroid synthesis and signaling in Drosophila 19
1.5.1 Ecdysone signaling overview 19
1.5.2 Ecdysone synthesis: The Halloween gene family 22
1.5.3 Ecdysone receptor structure and mechanism 25
1.5.4 Ecdysone as a promoter of growth 27
1.6 Scope of dissertation 28
Chapter 2. Local ecdysone synthesis in a wounded epithelium sustains
developmental delay and promote regeneration in Drosophila 30
2.1 Abstract 30
2.2 Introduction 31
2.3 Results 32
2.4 Discussion 54
2.5 Materials and Methods 59
Chapter 3. Validation of an EcR probe for tissue-specific disruption of
endogenous LBD-dependent interactions and support for additional EcR
roles in wing disc regeneration 67
3.1 Introduction 67
3.2 Results 71
3.3 Discussion 83
3.4 Materials and Methods 85
Chapter 4. Discussion and future directions 88
4.1 Summary of dissertation 88
4.2 Outstanding questions and future directions 89
4.3 Concluding remarks 94
References 96
About this Dissertation
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File download under embargo until 16 August 2025 | 2023-07-05 16:01:18 -0400 | File download under embargo until 16 August 2025 |
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