Figure 5. BrdU incorporation during midgut metamorphosis in Aedes aegypti 4th instars exposed to 100 μg/ml BrdU for the time intervals indicated below. Staining was performed as described in the Methods. BrdU labeled large nuclei are indicated by a downward pointing arrow head. Intermediate sized nuclei are indicated by an upward pointing arrow head. Small oval nuclei are indicated by left pointing arrow. All images were taken at the same magnification and scale bar represents 100 μm. (a) Anterior midgut of 4th instar exposed to BrdU from the time of molt to 14 hours after the molt, showing large, intermediate sized and small oval nuclei incorporated BrdU. (b) Same field as in Figure 4a but illuminated to detect DAPI staining. Most large nuclei were brightly fluorescent but not BrdU labeled. (c) Anterior midgut of 4th instar exposed to BrdU from 14 to 24 hours after the molt. Large, intermediate sized and small oval nuclei incorporated BrdU. (d) Posterior midgut of 4th instar exposed to BrdU from 14 to 24 hours after the molt. Incorporation by small oval nuclei greater than in Figure 5c. A few intermediate sized nuclei incorporated BrdU. (e) Anterior midgut of 4th instar exposed to BrdU from 24 to 36 hours after the molt. BrdU incorporation was predominately in small oval nuclei. (f) Posterior midgut of 4th instar exposed to BrdU from 24 to 36 hours after the molt. Labeled small oval nuclei were more numerous but a few intermediate sized cells were labeled. (g) Anterior midgut of 4th instar exposed to BrdU from 38 to 48 hours after the molt showed very little incorporation. (h) Posterior midgut of 4th instar exposed to BrdU from 38 to 48 hours after the molt showed many labeled diploid nuclei and no labeled large nuclei.