MYBL2 and ATM suppress replication stress in pluripotent stem cells (2021)
Figure 4

Figure 4. ATM kinase and MYBL2 function to regulate replication in pluripotent stem cells.

A) Scheme of the protocol. ESCs were treated with 10µM KU60019 for 1.5 hours before sequential addition of IdU and CldU for 20 minutes each. DNA was treated and visualised as previously described.

B) Distribution of replication rate after treatment with/without ATM inhibitor. Statistical analysis of distributions was carried out using an unpaired Mann Whitney U test. n=4. A minimum of 270 forks was measured for each condition ( **** p< 0.0001).

C) Distribution of the average IdU/CldU ratio in Mybl2+/+ and Mybl2Δ/Δ ESCs with or without ATM inhibitor treatment. Percentage of highly unstable forks (ratio above 2) are indicated. Dotted line at 1 indicates positive ratio. Y-axis was cut to change scale and display large values. Statistical analysis was carried out using the Mann Whitney U. At least 260 ratios were calculated per treatment group from 4 separate experiments ( **** p< 0.0001).

D) Frequency of new fired origins for Mybl2+/+ and Mybl2Δ/Δ ESCs with or without ATM inhibitor treatment. Error bars represent SEM. Statistical analysis was carried out using unpaired t-test. At least 500 replication structures were counted per treatment group from 4 separate repeats.

E) Frequency of anaphases positive for UFB positive cells (based on ERCC/PICH positive immunostaining) for Mybl2+/+, the Mybl2Δ/Δ and the Mybl2+/+ treated for 2 hours with ATM inhibitor (KU60019). Data represents at least 100 anaphases from each group from 2 experimental repeats. Statistical analysis was performed using an unpaired two-tailed t-test.

F) Immunoblot showing the levels of phosphorylated ATM (Ser1987) and ATM in the Mybl2+/+ and Mybl2Δ/Δ ESCs with or without CPT treatment (10µM CPT for 2 hours). Bar graph (lower panel) represents average band density of P-ATM in Mybl2Δ/Δ ESCs treated with CPT relative to ATM and relative to wild type CPT treated cells from three independent repeats. Error bars represent SD. Statistical analysis was carried out using a two-tailed unpaired t-test.

G) Distribution plot of replication speed in Mybl2+/+and ATM-/- ESC treated or not for 90 minutes with 10µM KU60019 (ATMi), before sequential addition of IdU and CldU for 20 minutes each. Statistical analysis was carried out using the Mann Whitney U test. At least 200 replication forks were counted from 3 separate experiments for wild type and ATM-/- and two separate experiments for ATM-/- treated with ATM inhibitor . ( **** p< 0.0001)

H) Quantification of the number of replication factories per cell for the different genotypes and treatments. A minimum of 65 early S-phase nuclei were counted per condition from two independent repeats. Statistical analysis was performed using a two-tailed unpaired unequal variance t-test.( **** p< 0.0001)

I) Distribution plot of replication speed in human iPSC and MEFs (primary and immortal). Statistical analysis was carried out using the Mann Whitney U test. At least 400 replication forks for iPSC,200 for primary MEFS and 250 for immortal MEFs were counted from 3 independent experiments. ( **** p< 0.0001)