Fig. 2

Heterochromatin-dependent gene silencing is not required for cell cycle exit. A, B RNAi to E(z) was expressed in the posterior wing from the L3 stage until the indicated time points in metamorphosis. Postmitotic wings at 26–28 h were examined for mitoses as indicated by phospho-Ser10-histone H3, PH3 (A), H3K27me3 (A′) and de-repression of Ubx (B). C RNAi to Su(var)205 (the gene encoding HP1) was overexpressed in the posterior wing, and postmitotic tissues were immunostained for PH3 and HP1 (C′). These conditions led to loss of HP1 and disrupted heterochromatin-mediated silencing of the Y10C reporter (D). Control RNAi (to the white gene), E(z) and/or Su(var)205 was expressed in the posterior wing in combination with E2F from the start of metamorphosis. Postmitotic wings at 42–44 h were dissected and examined for H3K27me3 (G, M), HP1 (J, N) and PH3 (F, I, L, O). E, H, K Flow cytometry was also performed to measure cells that enter S and G2 phases. Green trace indicates cells from the posterior wing expressing the indicated transgenes. Black trace: control non-expressing anterior wing cells. Reduced heterochromatin gene silencing does not compromise G0 even in the presence of high E2F activity. Scale bars = 50 μm A–D, F, I, L and O; 10 μm G, J, M and N