The steroid hormone ecdysone (Ec) is secreted from the prothoracic gland for growth in the developing Drosophila larva. How Ec-dependent regeneration can occur despite a drop in circulating Ec in the injured developing larvae remains unclear. In a new study in Development, Kenneth Moberg and colleagues find that injury induces local Ec synthesis at the wounded site to delay development and promote tissue repair in Drosophila. To learn more about the story behind the paper, we caught up with first author Douglas Terry and corresponding author Kenneth Moberg, Professor of Cell Biology at Emory University School of Medicine, USA.
Kenneth Moberg (left) and Douglas Terry (right). Credit: Colby Schweibenz.
Ken, can you give us your scientific biography and the questions your lab is trying to answer?
KM: I did my PhD training with Jackie Lees at the MIT Center for Cancer Research (now the David H. Koch Institute for Integrative Cancer Research at MIT), where I worked on the E2F family of transcription factors and the Rb family of proteins that regulate them. This work got me interested in how core cell cycle machinery is subordinated to developmental signals that pattern growth in developing multicellular organisms, so I joined Iswar Hariharan's lab at the Massachusetts General Hospital (MGH) Cancer Center to look for genes that inhibit growth in the fruit fly, Drosophila melanogaster. That led to the identification of the Archipelago protein as the specificity subunit of a ubiquitin ligase that degrades Cyclin E (and later found to degrade Myc). The Archipelago homolog FBXW7 was subsequently shown to target the same proteins for degradation in human cells and is now routinely sequenced in biopsied samples from cancer patients. The molecules my own lab studies have evolved over the years, but we remain interested in growth control.
Douglas, how did you come to work in the lab and what drives your research today?
DT: Following my undergraduate studies, I performed clinical chemistry research as an ORISE Fellow at the Centers for Disease Control and Prevention (CDC) and then for a small biotech company. After these experiences using biomarkers to perform diagnostic research, I wanted to shift my graduate studies to focus on the fundamental molecular biology that produces and uses such molecules. Ken's research with Drosophila drew me in because it presented the opportunity to probe the molecular pathways that coordinate local growth perturbations with systemic changes in growth and development. These same questions drive my research today as I continue to study local and systemic growth control, now in the Drosophila and murine intestine.
What is the background of the field that inspired your work?
KM: This current story was born out of an interesting paradox that proliferation of cells to restore missing tissue (i.e. regenerative growth) is associated with a systemic drop in the pro-proliferative hormone ecdysone. Ecdysone production had long been considered the sole domain of the prothoracic gland, but intriguing work from several labs, including the Schupbach and Irvine labs, had found examples of other sources of ecdysone that act locally near their site of production. We were thus curious whether the systemic drop in ecdysone after injury might be offset by local production of ecdysone at the site of regeneration.
We were curious whether the systemic drop in ecdysone after injury might be offset by local production of ecdysone at the site of regeneration
Can you give us the key results of the paper in a paragraph?
KM: We've defined a requirement for local synthesis of the steroid hormone ecdysone in injury-induced developmental delay and regeneration. These findings indicate that the wing disc blastema is a specialized signalling environment that requires local production of ecdysone. The data extend our understanding of how steroid hormone signalling can act locally or systemically to control development and, in this case, tissue renewal.
Douglas, when doing the research, did you have any particular result or eureka moment that has stuck with you?
DT: It was pretty early on in this project. I was performing confocal microscopy imaging to investigate what molecular pathways are turned on following injury to the fly wing disc. This consists of hours spent alone in a dark room scanning through slides of stained wing discs (vibing to Grateful Dead helps). But I remember seeing the increased expression of ecdysone receptor (EcR) activity reporter in the area of regeneration and thinking, oh wow I am seeing something new here… This was further confirmed by Ken's whoop of joy when I showed him the images.
EcR activity is downregulated in uninjured regions of L3 wing discs but upregulated locally at the site of injury and surrounding cells. Anti-βGal staining to detect activity of the EcRE-lacZ reporter in an uninjured L3 wing (left) and an L3 disc after injury to the pouch region (right).
And what about the flipside: any moments of frustration or despair?
DT: It wouldn't be a story about science without some frustration or despair. As we were putting together this story, we became particularly interested in discovering the molecular connection between depletion of local ecdysone signalling in the regenerating tissue and the subsequent loss of systemic coordinated growth reduction we observed. A signalling peptide called Ilp8 had been shown through lovely research by several labs to be produced at the site of regeneration in the wing disc and to signal through neurons in the fly brain to control developmental progression. Perfect, queue up the models with local ecdysone signalling upstream of Ilp8 production in the regenerating tissue. Alas, when I tested levels of Ilp8 in our injured wing discs, I found it completely unresponsive to our local ecdysone signalling perturbation. Months of frustration, rereading the relevant literature, and testing other possibilities eventually led us to the finding that the regeneration regulators Upd3 and Ets21C are responsive to local ecdysone signalling.
It wouldn't be a story about science without some frustration or despair
Why did you choose to submit this paper to Development?
KM: As pressure to fund translational science is growing in the US, we viewed Development as the perfect place to send our paper. The journal has a long history of supporting the developmental biology community and has a wide readership that we hoped would be interested in the work.
Douglas, what is next for you after this paper?
DT: I am currently performing a postdoctoral fellowship in the lab of Brian Robinson, MD/PhD. Here, I am continuing to study regeneration, now in the context of the Drosophila and murine intestine. The molecular pathways responsible for the crosstalk between the local and systemic environments during growth perturbations continue to drive my interest.
Ken, where will this story take your lab next?
KM: The ecdysone receptor EcR is linked to a rather large transcriptional programme in the larval wing disc that changes over time, presumably in response to changing ecdysone levels. Our finding that EcR is locally activated in injured wing discs implies that it may be an important contributor to the regeneration-specific transcriptome. That's an area of interest for us now.
Finally, let's move outside the lab – what do you like to do in your spare time?
KM: Atlanta is a great city for outdoor activities. The climate is warm, and the city is the most heavily forested of all major US cities. I spend weekends with my wife and kids hiking and enjoying our local restaurant and brewery scene. I'm currently trying to plan a fly-fishing trip with my son in the North Georgia mountains.
DT: During graduate school I was invited by senior grad students to play intramural volleyball. It had been years since I had played a team sport, but I quickly found the camaraderie of bump-set-spiking addictive. Some serendipitous meetups later led me to find a strong community playing grass volleyball in the many parks scattered across Atlanta. Now you'll find me out playing volleyball as often as the weather and my poor legs allow.
D.T.: Graduate Programs in Genetics and Molecular Biology, Laney Graduate School, Emory University, Atlanta, GA 30322, USA.
D.T. & K.M.: Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.
E-mail: [email protected]
