(A-I) Images show distal tip of AGs from 6-day-old adult virgin males expressing nuclear GFP alone (control; this also stains the cytosol; A) or in combination with additional transgenes in SCs under the control of the esgtsF/O driver and stained for EdU incorporation. Nuclei are stained with DAPI (blue). Red arrows point to pairs of EdU+ SC nuclei and yellow arrows point to pairs of EdU- SC nuclei for each transgene (or in some cases, single nuclei when RbfCA is expressed). (J-O) Bar charts depicting mean % of EdU+ SCs per gland (J-L), the geometric mean SC:MC nuclear area (M, N), mean SC:MC nuclear area (O) of virgin males for control glands and glands expressing different transgenes in SCs. E2F1-mediated endoreplication in SCs requires ecdysone-independent EcR signalling (C, D, H-J, L). However, E2F1 can promote some growth in SCs independently of EcR (D, I, M, O). Rbf and EcR may partially act independently of each other, at least to regulate SC growth (E-G, K, N). E2F1’s effects on growth and endoreplication do not appear to require ecdysone, which is required for normal SC growth in virgin males (H, I, L, O). Kruskal Wallis test; Dunn’s post hoc test (J-L). Welch ANOVA on log-transformed data; Games-Howell post hoc test (M-N). Welch ANOVA; Games-Howell post hoc test (O). n≥7 glands (J); n≥11 glands (K); n≥7 glands (L); n≥15 cells (M); n≥39 cells (N); n≥15 cells (O). Scale bars correspond to 20 μm. The error bars show the standard deviation (J-L, O) and the geometric standard deviation (M-N) within the sample. 0.01<*p<0.05; 0.001<**p≤0.01; 0.0001<***p≤0.001; ****p≤0.0001.