Regeneration Induction in Drosophila Limb Promoted by Nutrient Factors

Author: Li, Yutian

Year: 2027

Degree: Dissertation (Ph.D.)

Advisor: Goentoro, Lea A.

Committee Members: Hay, Bruce A.; Elowitz, Michael B.; Zernicka-Goetz, Magdalena; Goentoro, Lea A.

Option: Biology

Abstract

Regeneration is a remarkable yet highly variable trait across tissue types and animals. This contrast raises a central question in biology: is regenerative capacity truly lost in poorly regenerating animals, or can it be reactivated under the appropriate physiological conditions? In this thesis, I investigated whether specific factors can induce appendage regeneration in animals with poor regenerative capacity, and how this regeneration activation is coordinated at both the tissue and organismal levels.

I first tested this question in animal species across the animal phylogeny: jellyfish, fruit flies, and mice. Although these animals do not normally regenerate appendages, through screening, we observed initiation of appendage regeneration when they were administered leucine, glutamine, and insulin. Although the induced regeneration is not complete, the key finding is that providing nutrient factors is sufficient to activate regeneration across evolutionarily distant species. The cross-species response suggests that regenerative programs are not fundamentally lost during evolution, but instead remain latent and can be reactivated upon favorable metabolic conditions.

Motivated by the potential use of Drosophila for investigating novel and conserved pathways in regeneration induction, I further characterized the regeneration induction. Although limb regrowth could take months, the decision to initiate regeneration processes is made within hours after injury, manifested in altered wound healing. At day-scale, while tissues in the injured limb segment normally degenerate, tissues in nutrient-supplemented flies survive. At week-scale, regenerative growth is preceded by a dome-shaped protrusion at the injury site. Performing single-nucleus RNA sequencing in the limb at this stage, I find widespread transcriptional modulations across cell types, and distinct cell populations within the muscle and epithelial cells that are enriched in mitotic and morphogenetic genes. This evidence across multiple time scales reveals how nutrient supplements can remodel the cells to reverse tissue loss and reactivate tissue replenishment.

Because nutrients act on the whole organism, I next investigated whether regeneration activation is accompanied by systemic remodeling, including changes at the organ level. Indeed, regenerating flies enlarge their gut, which is a known mechanism to adapt to increased demands. In parallel, flies that activate regeneration reduce ovary size and egg chamber maturation. Consistent with the trade-off between activating regeneration and sustaining reproduction, virgin flies are more responsive to treatment. To further dissect candidate systemic regulators, I performed whole-organism transcriptomic profiling to identify the earliest processes that accompany the reactivation of regeneration. This analysis reveals steroid hormone signaling as one of the most highly upregulated signaling pathways. Because steroid hormone signaling is sensitive to nutritional status and interacts closely with insulin signaling to regulate systemic metabolism, these findings suggest that nutrient-induced regeneration involves not only local tissue remodeling, but also systemic organ remodeling and organism-wide resource reallocation.

In summary, my thesis identifies nutrient factors as a conserved strategy for inducing regeneration across evolutionarily distant species. By careful examination of gene-, cell- and tissue-level changes accompanying regeneration induction, I establish adult Drosophila as a tractable model to further dissect regeneration activation. Lastly, the role of nutrients further reveals that regeneration activation is a whole-body response that integrates nutrient sensing, systemic organ remodeling, and organism-wide resource reallocation.