Local ecdysone synthesis in a wounded epithelium sustains developmental delay and promotes regeneration in Drosophila Restricted; Files Only

Terry, Douglas (Summer 2023)

Permanent URL: https://etd.library.emory.edu/concern/etds/1v53jz32h?locale=en


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

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