Journal: Nature
Article Title: Replication-stress-induced chromatin loops protect fork stability
doi: 10.1038/s41586-026-10695-1
Figure Lengend Snippet: a , Representative locus (chr8: 122.8-133.9 Mb). Top: Hi-C heatmap (red squares highlight positions of loop anchors). Below: Fork-Deg-seq signal (HCT116-CTCF-mAID2-mClover cells) untreated or treated with G9ai (4 h), 5-Ph-IAA (4 h, CTCF-dep) or both upon 4 mM HU (5 h or 8 h), alongside MRC5 CTCF and H3K9me3 Rep-ChIC signals, IZs and fragile sites. Black arrowheads indicate high Fork-Deg-seq signal. Shaded area: loop-dense region with reduced degradation; unshaded areas show increased degradation. b , Aggregate mean Fork-Deg-seq signal ± s.d. after 5 h 4 mM HU within HU-unique loops ± 5 kb in HCT116-CTCF-mAID2-mClover cells. Results shown are from one representative experiment which has been performed 2 times with similar results. c-e , Distribution of IZs at early [n = 2119] and late [n = 2193] replicating fragile sites. ( c ) HU-unique loops overlapping IZs (MRC5), ****P ≤ 0.0001, (Two-sided Mann–Whitney U test, p-value: 7.858e-38). ( d ) Fork-Deg-seq signal in HCT116 IZs, ****P ≤ 0.0001, (Two-sided Mann–Whitney U test, p-values: 1.222e-07, 6.247e-06, 1.161e-05, 6.247e-06 left to right). ( e ) Fork-Deg-seq signal in RPE1 IZs (RPE1-shBRCA2 cells), ****P ≤ 0.0001, (Two-sided Mann–Whitney U test, p-values: 3.119e-37 WT + HU and 2.080e-55 shBRCA2+HU). f , Representative electron micrographs showing a reversed fork with ssDNA gaps on both daughter strands and intact reversed arms (HCT116-CTCF-mAID2-mClover). P, parental strand; D, daughter strand; R, reversed arms. Scale bars: 250 nm or 1183 bp (main), 50 nm or 473 bp (insets). g , Ranked gap length distribution per condition. h , qPCR analysis of HU-unique loop formation in WT and TKO (SMARCAL1, ZRANB3, HLTF knockout) U2OS cells ± 4 mM HU. Means ± s.e.m. [n = 4 independent biological replicates]. ****P < 0.0001, ***P < 0.001, **P < 0.01, ns=non-significant (Ordinary one-way ANOVA, Tukey’s test, P value from top to bottom: a: <0.0001, 0.0026, 0.4735; b: 0.0003, 0.0095, 0.5794; c: 0.004, 0.1237, 0.3688; d: <0.0001, 0.0471, 0.1211; e: <0.0001, 0.0003, 0.0752; f: 0.0004, 0.0003, 0.5844; g: <0.0001, 0.0042, 0.4301; h: 0.0003, 0.0004, 0.935; i: <0.0001, 0.0019, 0.4734,; j: 0.0006, 0.0001, 0.6204; k: 0.0005, 0.0206, 0.4417; l: <0.0001, 0.0032, 0.3017; m: <0.0001, 0.0173, 0.269; n: 0.0013, 0.0074, 0.8887; o: 0.0013, 0.0074, 0.7701; p: 0.0003, 0.095, 0.1693). i , Top: Schematic showing that only H3K9me3 signal intensity overlapping with EdU was measured. Bottom: Distribution of H3K9me3 intensity in the region of interest and for the indicated conditions. Number of replication sites analysed per condition across two independent experiments: n = 148, 98, 111, 107, 103 and 84 from left to right. (*: p < 0.05, ****: p < 0.0001, ns: non-significant. Kruskal–Wallis test followed by Dunn’s test, P values: 0.0160, <0.0001, <0.0001, >0.9999, 0.7905, >0.9999, 0.0946, >0.9999 and 0.0156 (top to bottom)). j , Top: Schematic showing that only the H3K9me3 signal intensity just outside of the EdU track was measure (H3K9me3 intensity over a region covering 20% of the total length of the EdU track was measured on both side of the EdU track). Bottom: Distribution of H3K9me3 intensity in the region of interest and for the indicated conditions. Number of replication sites analysed per condition across two independent experiments: n = 98, 119, 107 and 103 from left to right. (***: p < 0.001, ****: p < 0.0001, ns: non-significant. Kruskal–Wallis test followed by Dunn’s test, P values: <0.0001, 0.7726, 0.4606, 0.0003, <0.0001 and <0.0001 (top to bottom). k , Total intensity distribution of CTCF-EdU PLA spots. S-phase nuclei analysed: n = 642 for all conditions imaged from one representative experiment, which has been performed 2 times with similar results. Red line marks mean. ****P ≤ 0.0001, **P ≤ 0.01, ns=non-significant (Kruskal–Wallis, Dunn’s test, P values from left to right: <0.0001, <0.0001, 0.0011, <0.0001, <0.0001, 0.1690).
Article Snippet: In experiments using HCT116 cells expressing CTCF-mAID2-mClover, the culture medium was replaced with medium containing 1 μM 5-Ph-IAA (HY-134653, MedChemExpress) for at least 2 h before the experiment to induce transient depletion of CTCF.
Techniques: Hi-C, MANN-WHITNEY, Knock-Out