Research Overview

The Genetics of Tissue Regeneration

Most human tissues damaged by traumatic injury or disease do not regenerate, and current strategies to promote regeneration are limited. The ability to extensively repair and regrow damaged or missing tissue occurs frequently in other species, even in equivalent organs that have little to no regenerative capacity in people. Understanding what gives a tissue the ability to regenerate is an essential step towards developing therapeutic interventions to improve healing outcomes. However, the basic underlying genetic events that permit damage-induced regeneration remain unknown. This includes both the identities of factors required for tissue regrowth, and the regulatory events that lead to their appropriate activity throughout the regeneration process. Thus, the overall goal of our lab is to characterize the fundamental genetic mechanisms that allow tissues to regenerate, with a view to developing methods to enhance regenerative ability.

In order to study regeneration, we use the well established and exceptionally powerful genetic model organism Drosophila melanogaster, the common fruit fly. The larval organs of Drosophila, known as imaginal discs, are able to regenerate following various types of damage, including physical injury, irradiation, and genetically-induced damage.

The wing imaginal disc, which forms the adult wing structures, is an epithelial organ that has been extensively studied as a model for tissue growth and development. The strong conservation of genetic pathways and the similarities in regenerative processes between Drosophila and mammals ensure findings made in this context are likely to ultimately have relevance to regeneration in humans.

Genetically inducing tissue damage and stimulating regeneration

Investigation of wing disc regeneration has been transformed by the development of genetic ablation systems, which  allow researchers to induce reliable and reproducible imaginal disc damage that subsequently stimulates disc regeneration in vivo. However, existing ablation systems often rely on tissue-specific GAL4 expression to induce UAS-driven apoptosis, limiting the simultanous use of other GAL4 or UAS-based reagents that are prevalent in Drosophila research.  Thus, existing methodologies lack the ability to target regenerating cells for genetic manipulations. To overcome this, we pioneered a novel genetic ablation system that overcomes these limitations, called DUAL Control. 

To allow gene manipulation to be independent of ablation, we generated a system based on a split version of LexA, in which ablation is achieved using two transgenes that encode separate halves of a transcriptional activator (LexA:DBD and p65). Each half contributes either spatial or temporal control over expression: a tissue-specific spalt (salm) enhancer drives one half in the distal wing pouch, while a heat shock promoter directs expression of a p65 transcriptional activator domain.  A short heat shock triggers p65 expression, leading to the temporary formation of the full transcriptional activator only in the distal pouch. This transcriptional activator then drives expression of any lexAop-transgene, including those we have developed to cause cell death via apoptosis (via JNK signaling or independent of JNK) and necrosis (via different leaky or activated ion channels). 

This system is compatible with all current GAL/UAS tools, but to target regenerating cells for genetic manipulation we have also engineered a GAL4 transgene (DVE>>GAL4) that drives expression in the cells surrounding the injury that contribute to the newly regenerated tissue. A “STOP” cassette (denoted by >>) prevent its expression until heat shock-induced FLP mediates its removal. Thus, a single heat shock initiates a burst of ablation followed by continuous UAS-driven transgene expression in the regenerating pouch that can be used to interrogate the role of almost any gene in Drosophila.  

Events of regeneration can be examined through immunofluorescent imaging of disc tissues at any point during the process, while overall regeneration can be rapidly assayed by simply evaluating adult wing size, binning into discrete categories or measuring wing area for statistical quantification. Thus, DUAL Control is a powerful tool to explore regeneration, which we are using to 1) investigate regulators of tissue regrowth and comprehensively map changes in regenerative capacity of this tissue, and 2) compare how different forms of injury originating from either programmed cell death (apoptosis) or catastrophic lytic cell death (necrosis) influence the regenerative process.  

See the projects page for details of these specific areas of research.