Figure 1. Epithelial damage induces extra endoreplication in ECs.

(a–d) Midguts of 3–5-day-old flies were stained with DAPI (blue) to visualize DNA. Representative images of (a) uninfected controls and (b) individuals that were infected with P.e. for 1 day. The majority of nuclei present in the midgut epithelium are EC nuclei. Quantification of EC nuclear DNA content (c,d) measured by integrated fluorescent intensity per nucleus from 10 midguts per genotype. P.e. infection led to higher EC ploidies. EE, enteroendocrine cell. (e,f) The esgF/O flies were shifted from 18 to 29 °C for 24 h. The esg-Gal4 drove expression of UAS-GFP and UAS-flp that in turn led to act-Gal4 and GFP expression in all esg+ cells and their newborn progeny. After 24 h, these flies were fed P.e. and EdU in sucrose solution for 8 h. (e) Midguts were labelled with DAPI to visualize DNA (blue) and incorporated EdU (red) to identify endocycling cells. All esg+ cells and their daughters produced during the experiment expressed GFP (green). (f) Quantification of EdU incorporation for 15 guts. Thus, 95% of EdU⁺ cells were GFP⁺, while ∼5% of EdU⁺ cells did not express GFP. ****P value from Student's t-test (P<0.0001); n=10. All experiments were repeated twice. (g) Survival curve showing that blocking endoreplication in EBs and pre-ECs reduces lifespan. Geminin or DNA polymerase-α (Pol α RNAi (inverted repeat (IR)) was overexpressed in EBs and pre-ECs using Su(H)GBE-Gal4. Dashed lines represent control flies raised in normal food with sucrose; solid lines represent experimental flies raised in food with P.e. bacteria.