Fig. 1. The role of cell cycle progression in the control of dap expression. dap expression was analyzed by in situ hybridization in wild-type embryos (A,B), mutant embryos lacking both CycA and CycB (C,D), and embryos expressing UAS-CycE under the control of prd-GAL4 (E,F). Cells in the dorsolateral epidermis arrest in G1 of cycle 17 in wild type, prematurely in G2 of cycle 15 in CycA CycB double mutants, or too late after an extra division cycle 17 in the UAS-CycE expressing segments of prd-GAL4 UAS-CycE embryos. These variations in the cell proliferation program do not affect the program of dap transcription during stage 11 (compare A,C,E). The high-magnification views (B,D) illustrate that the nuclear density in the CycA CycB double mutants (D) is half of that in wild type (B) because of the premature cell cycle arrest. The high magnification view of two epidermal segments at stage 12 (F) illustrates that the disappearance of dap transcripts is delayed in the prd-GAL4 UAS-CycE expressing segments (right side).