Insulin and TOR signal in parallel through FOXO and S6K to promote epithelial wound healing

Abstract

The TOR and Insulin/IGF signalling (IIS) network controls growth, metabolism and ageing. Although reducing TOR or insulin signalling can be beneficial for ageing, it can be detrimental for wound healing, but the reasons for this difference are unknown. Here we show that IIS is activated in the cells surrounding an epidermal wound in Drosophila melanogaster larvae, resulting in PI3K activation and redistribution of the transcription factor FOXO. Insulin and TOR signalling are independently necessary for normal wound healing, with FOXO and S6K as their respective effectors. IIS is specifically required in cells surrounding the wound, and the effect is independent of glycogen metabolism. Insulin signalling is needed for the efficient assembly of an actomyosin cable around the wound, and constitutively active myosin II regulatory light chain suppresses the effects of reduced IIS. These findings may have implications for the role of insulin signalling and FOXO activation in diabetic wound healing.

Long-termin vivoimaging ofDrosophilalarvae

“…The transgenic tools like Gal4 drivers, fluorescently tagged proteins and other markers, which were originally developed and established for studies in embryos can also be used for larvae. In addition, larvae are resilient to heat-shock or UV irradiation, the methods used to induce mosaic clones and to control temperature sensitive protein function and optogenetic tools 34,[36][37][38] .…”

“…Finally, it is easy to treat larvae with drugs, such as rapamycin, chloroquine, bafilomycin A1, wormatin, blebbistatin and many others, which can simply be administered by including them in the food 34,[57][58][59] . The larva therefore represents an attractive in vivo model both for fundamental and medically relevant questions.…”

“…For all our live imaging we used an inverted spinning disk confocal microscope as described above (section Materials/Microscope) 34…”

“…image epidermal wound healing in larvae, use either: w 1118 ; e22c-Gal4, UAS-Src-GFP, UAS-DsRed2-Nuc/CyO; + or: w 1118 ; +; A58-Gal4, UAS-Src-GFP, UAS-DsRed2-Nuc/TM6B flies.In both lines, the plasma membrane is marked by Src-GFP and nuclei by DsRed2-Nuc34,61 .Both drivers, e22c-Gal4 and A58-Gal4, are expressed in the epidermis. e22c-Gal4 is expressed from embryonic stage 10-11 onward and A58-Gal4 from the first larval instar onward 61, 70 .2To visualise the adherens junctions for laser ablations at cell interfaces, use a transgenic line, in which endogenous DE-Cad is marked by GFP (w 1118 , y -; endo:DEcad-GFP; +)71 .…”

Repair, regenerate and reconstruct: meeting the state-of-the-art

“…The link between nutrition control and early regeneration has been examined by Maria Leptin (University of Cologne and the European Molecular Biology Laboratory, Germany). She showed that signalling through the insulin receptor (InR) and TOR is necessary for epithelial organization during wound healing in Drosophila (Kakanj et al, 2016). The insulin pathway activates Pi3K and FOXO, whereas the TOR pathway operates through the Atg1/Atg13 autophagy machinery.…”