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. 2021 May 7;9:656795. doi: 10.3389/fcell.2021.656795

FIGURE 1.

FIGURE 1

The catalytic activity of cytolethal distending toxin (CDT) induces a replicative stress. (A) Cells were incubated or not with CDT holotoxins during several hours before successive pulse labeling with 5-chlorodeoxyuridine (CldU) and 5 iododeoxyuridine (IdU). Then, replication fork speed was analyzed by DNA fiber assay. IdU track length was determined. (B–D) Upper panel: representative images of replication tracks: CldU (red) and IdU (green) (n > 400 IdU tracks were measured with a wide-field fluorescent microscope, original magnification × 40, scale bar: 10 μm). Lower panel: horizontal red lines represent the median (**P < 0.01, ****P < 0.0001). (B) HeLa cells were treated or not (NT) with 100 pg/ml or 2.5 ng/ml of CDT from E. coli for 16 h before IdU and CldU staining. (C) U2OS cells were treated or not with the same doses of CDT from H. ducreyi for 24 h before the replication staining. (D) U2OS cells were treated or not with 2.5 ng/ml of wild-type (WT) or catalytically inactive mutant (Mut) of CDT from H. ducreyi for 24 h before IdU and CldU incorporation.