Figure 4: Bptf is required for MYC-induced proliferation of MEFs and replication stress but not for apoptosis.

(a) WT (n=4) and Bpft-null (n=4) MEFs transduced with MYC-ER were seeded at high density, arrested with 0.5% FBS for 48 h and stimulated with serum in the presence/absence of 4-OHT. At the indicated time points, cells were pulse labelled with BrdU for 1 h before collected. Data are represented as mean±s.e.m. ***P<0.001 (paired t-test). (b) Histograms depicting the ploidy of BrdU-positive cells throughout the experiment described in a. (c) Quantification of early S-phase cells. The rate of loss of BrdU⁺ early S-phase cells represents S-phase progression. Data are represented as mean±s.e.m. *P<0.05; ***P<0.001 (unpaired t-test). (d) Replication stress—intensity of γH2AX signal in WT and Bpft-null MYC-ER MEFs (n=3 per group) in the presence or absence of 4-OHT for 48 h. Doxorubicin-treated cells were used as control. *P<0.05 (paired t-test) (e) WT (n≤4) and Bpft-null (n≤4) MEFs expressing MYC-ER were seeded at high density and then transferred to 0.5% FBS with or without 4-OHT (2μM). Apoptosis was measured as the proportion of Annexin V-postivive cells at the indicated time points. *P<0.05; **P<0.01; ***P<0.001 (paired t-test to compare vehicle versus 4-OHT; unpaired t-test to compare WT versus Bptf-null cells).