Swatting flies: modelling wound healing and inflammation in Drosophila

Abstract

Aberrant wound healing can lead to a variety of human pathologies, from non-healing chronic wounds that can become dangerously infected, to exuberant fibrotic healing in which repair is accompanied by excessive inflammation. To guide therapeutic intervention, we need a better understanding of the fundamental mechanisms driving tissue repair; this will require complementary wound-healing studies in several model organisms. Drosophila has been used to model genetic aspects of numerous human pathologies, and is being used increasingly to gain insight into the molecular and genetic aspects of tissue repair and inflammation, which have classically been modelled in mice or cultured cells. This review discusses the advantages and disadvantages of Drosophila as a wound-healing model, as well as some exciting new research opportunities that will be enabled by its use.

Fig. 1.

At all stages of development, from embryo to adult, Drosophila can and has been used as a wound-healing model. Wounded areas are shown in red. (A) Embryos can be wounded by hand with a glass needle, which punctures the vitelline membrane (creating asterile wounds), resulting in ragged wounds that vary in size. Laser-mediated wounding ablates a patch of epithelium, leaving a circular hole of reproducible size that gapes in the dorsoventral axis because of tensions within the epithelium. These laser-mediated wounds leave the vitelline membrane intact and are therefore sterile. Embryo wounding is generally performed at around stage 14, when dorsal closure (horizontal oval represents dorsal hole) is near completion, enabling comparisons between wound healing and morphogenesis. (B) Larval wounding (generally third instar) is mediated either with a needle, which breaks the epidermal layer and results in the formation of a melanin clot, or by ‘pinching’ with forceps, which damages the epidermis, but does not breach the barrier cuticle. (C) Within third instar larvae are imaginal discs, which have long been used as a model of pattern regeneration. Wounding was historically mediated by mechanical cutting (broken red line) and required grafting back into an adult host, but new studies use Gal4-UAS-targeted apoptotic killing of defined populations of cells in the wing and/or leg discs. (D) At pupal stages, fly tissues are translucent and are amenable to wounding and dynamic imaging, but only after a window has been cut in the pupal case. (E) Finally, adult flies can be wounded using a tungsten needle or with iridectomy scissors, by cutting between the tergites of the abdomen.

Fig. 2.

Drosophila embryonic macrophages (haemocytes) migrate to wounds in the epithelium. (A) Time course series revealing haemocyte recruitment to the wound within 10 minutes and continuing for 90 minutes before this inflammatory response begins to resolve. Wound recruitment only occurs from stage 15 of fly embryonic development; before this stage, haemocytes seem to integrate wound signals and developmental dispersal cues in ways that suggest molecular mechanisms that enable haemocytes to ‘prioritise’ various attractant cues over others. The closing wound edge is highlighted by the dotted line. Adapted from Stramer et al. (Stramer et al., 2005) with permission. (B) Schematic illustrating the time course of events imaged in A. Epithelial cells at the wound edge rapidly assemble an actomyosin cable and dynamic lamellae and filopodia (red webbed and finger-like structures). Wounding also induces the production of hydrogen peroxide (represented by orange gradient), which acts as a robust chemoattractant for haemocytes in embryos. Haemocytes become polarised and oriented towards the wound via bundled microtubules (green) and initially accumulate at the wound edge before filling the wound space. As the wound closes and the chemoattractant gradient fades, haemocytes return to their developmental positions.