Fig. 6

20E injection induces DNA synthesis in the midguts. a–b Appearance of a larva (a) and dissected midgut (b) at 36 h post 4th ecdysis. The larva ingested food and the midgut was full of food. c-j Morphology of midguts and DNA synthesis at different time points of naïve larvae as observed by microscopy. 20E was injected at 12 h post 4th ecdysis (see next) and is labeled as 0 h. Correspondingly, at each time point indicated, microscopic morphology changes (c-f) and DNA synthesis (g-j) in naïve larvae were observed. BrdU was incorporated into midgut cells at 0 h (12 h post ecdysis) (g). After this time point, no cell incorporated BrdU. k-t Microscopic morphology of midguts and DNA synthesis at different time points after 20E injection. At 12 h after the fourth ecdysis, 20 μg of 20E was injected into each larva. k-l Appearance of a larva (k) and dissected midgut (l) at 24 h post 20E injection (equal to 36 h post ecdysis). The insect appeared to be in a molting state at 24 h post 20E injection (k), and the midgut was devoid of contents (l). Morphological changes (m–p) and DNA synthesis (q–t) were compared. Bubble-like structures (indicated by arrowheads) were produced at 36–48 h post injection of 20E (c–p). DNA synthesis was induced and also decreased over time (q–t). Bars: 5 mm (a, b, k, l) and 50 μm (c–j, m–t)