E2F transcriptional activation and Dp loss are highly similar, except for specific genes that require E2F activity for expression after exit. Using microarrays, we compared gene expression in E2F1–DP-expressing wings (ap-Gal4/UAS-E2F1, UAS-DP, tub-Gal80^TS) with controls (ap-Gal4/UAS, tub-Gal80^TS) and Dp mutant wings (w;Dp^a1/a2) with controls (w) at three time points. (A) Heat map of transcript changes (color range indicates the log₂ ratio of expression compared with controls). All transcripts with a fold change of 1.5 or more (>log₂ ± 0.6) at one or more time points are shown. Gray bars indicate transcripts that were removed from analysis because of high variability among independently replicated experiments (n = 4 for E2F; n = 3 for Dp^−/−). Transcripts were clustered using Genesis software for hierarchical clustering. Representative genes from each major cluster are listed on the right. Typical group transcripts are up-regulated in E2F-expressing and Dp^−/− wings at 24 and 36 h APF, whereas other transcripts are repressed or inversely regulated. Arrays for E2F and Dp^−/− at 24 and 36 h were highly similar with a correlation coefficient of 0.74. (B) A group of 162 genes was up-regulated >1.75-fold (>log₂ 0.82) by E2F activity at one or both time points APF but was not significantly increased in Dp^−/− (change <1.3-fold; <log₂ 0.4). Asterisks indicate examples of genes that regulate cyclin–Cdk activity or mitosis.