A-C. Immunofluorescence images of midgut section from the R4 region in 40-day flies (A), 40-day flies with spermidine administration started at 26th day after fly eclosion (B), 40-day flies with spermidine and ALA administration started at 26th day after fly eclosion (C). esg-GFP (green) indicates ISCs and their differentiating cells. Dl (red) staining was used to visualize ISCs. Data information: DAPI stained nuclei are shown in blue. Scale bars represent 10 μm 