Fig. 5. Time course of F-actin organization. White arrows indicate F-actin at the DV boundary, yellow arrows point to F-actin at the AP boundary. (A-E) Discs of different ages stained for F-actin, an anterior marker (ci-lacZ, blue) and a dorsal marker (Bx, red). The apical DV F-actin line coincides precisely with the DV boundary during early-mid third instar, but because Bx and nuclear ß-galactosidase are more basal, and cells are not perfectly vertical, the difference in focal planes gives a false impression in some cases of discordance between them. Larvae were staged from the beginning of the L2-L3 molt, and are shown at (A) 0-12 hours, (B) 12-24 hours, (C) 24-36 hours, (D) 36-48 hours and (E,F) 48-60 hours of third instar. The DV F-actin line is consistently observed from 0-24 hours of third instar (A,B). From 24-36 hours, F-actin is not consistently elevated, but cells still generally line up along the DV boundary (C). From 36-48 hours the DV boundary is no longer distinguishable by F-actin staining, but F-actin begins to appear elevated in flanking cells (D); this is even more obvious in older discs (E,F), and appears adjacent to late stripes of Dl expression (magenta, F).