Fig. 3: Fat body catabolism and nutrient release to hemolymph facilitates regenerative proliferation through mTORC signalling pathway.

A, B Nile Red staining (cyan/grey) of fat body dissected from larvae with control (A) or egr-expressing (B) wing discs. DAPI (magenta) visualises nuclei. C Mean area of lipid droplets in fat body dissected from larvae with control (A) or egr-expressing (B) wing discs. Mean and 95% CI, two-tailed Unpaired t test. p-value = 0.0004. (control: n = 15, egr-expression in discs: n = 18). D, E Triacylglycerides (TAG) levels in fat bodies dissected from larvae with egr-expressing wing disc, control or starved (16 h) larvae. Mean and 95% CI, One-way ANOVA followed by Dunnett’s test for multiple comparison (control larvae: n = 9, egr-expressing larvae: n = 9 and starved larvae: n = 4). p-values: control vs egr = 0.0353; control vs starved =0.0076. F, G ImpL2-GFP in control (A) and egr-expressing discs (B). DAPI visualises nuclei. H Mean ImpL2-GFP intensity in control (F) and egr-expressing discs (G). Mean and 95% CI, two-tailed Welch’s t test, p-value = 0.0001 (control: n = 9, egr-expressing discs: n = 11). I, J Nile Red staining of fat body (cyan/grey) from larvae with control (I) or ImpL2-expressing wing discs using rn-GAL4 (J). K Lipid droplet areas in fat body from larvae with either control or ImpL2-expressing wing discs using rn-GAL4 (24 h). Mean and 95% CI, two-tailed Mann-Whitney test, p-value < 0.0001 (control: n = 23, experiment: n = 18). L Heat map showing relative changes of metabolite concentrations in the larval hemolymph from control and egr-expressing larvae. Data were quantile normalised and analysed using a two-sided, unpaired Wilcoxon rank-sum test. Metabolites with at least < 0.75 and > 1.5-fold change were selected. Metabolites were ordered by log2 fold changes shown as Z-scores. Sample size n = 3 per condition. M, N CG5535-GFP in control (cyan/grey) (M) and egr-expressing discs (N). TRE-RFP visualises JNK- activity (magenta). O Mean CG5535-GFP intensity in the pouch of control and the proliferative domain of egr-expressing discs (PD^egr). Mean and 95% CI, two-tailed Unpaired t test, p-value = 0.0092 (control: n = 4, egr-expressing discs: n = 5). P, Q OPP visualises protein synthesis in egr-expressing wing discs from larvae fed on food without (P) or with rapamycin (200 μM) (Q) for 24 h during egr-expression. R. Mean OPP intensity in the pouch of control and the proliferative domain of egr-expressing discs (PD^egr) from larvae fed on food without or with rapamycin. Mean and 95% CI, One-way ANOVA followed by Tukey’s post-hoc test for multiple comparisons (control: non-fed: n = 9, fed: n = 10; egr-expressing disc: non-fed: n = 10, fed: n = 10). PD^egr vs PD^egr+ Rapamycin: p < 0.0001, Control + Rapamycin vs PD^egr+ Rapamycin: p = 0.0167 and Control vs Control + Rapamycin: p = 0.0017. S Model: ImpL2 from senescent-like cells in high JNK domain represses fat body anabolism via inducing insulin resistance, promoting nutrient mobilisation. This branch may reinforce the metabolic switch induced by Insulin restriction. Released nutrients (e.g., amino acids) enter hemolymph and support mTORC1/S6K activation in the proliferative domain. Scale bars: 100 μm. Fluorescence intensities are reported as arbitrary units. Source data in graphs are provided as a Source Data file. Illustrations were created in Biorender Classen, A. (2025) https://BioRender.com/h63vwwi.