Journal: bioRxiv

Article Title: Role of a childhood cancer-linked BRIP1/FANCJ germline variant in genomic instability and cancer cell vulnerability

doi: 10.64898/2026.03.24.714005

Figure Lengend Snippet: a, HCT116 cells stably expressing BRIP1 R162Q were transiently transfected using PEI with empty vector (EV-EGFP) or RNaseH1-WT-eGFP. Transfection efficiency was assessed via EGFP fluorescence. b, immunoblot analysis confirming expression of GFP-tagged constructs in transfected cells. c, Immunofluorescence detection of R-loops using the S9.6 antibody in cells transfected with EGFP or EGFP-RNaseH1. d, Quantification of S9.6 mean fluorescence intensity (MFI) per nucleus. Data represent mean ± SEM of three independent experiments. e, Immunofluorescence detection of G-quadruplex (G4) structures using the BG4 antibody in cells transfected with EGFP or EGFP-RNaseH1. f, Quantification of BG4 fluorescence intensity per nucleus. Data represent mean ± SEM of three independent experiments. g, Representative DNA fiber assay images from HCT116 cells harboring BRIP1 R162Q transfected with empty vector (EV-eGFP) or RNaseH1-WT. DNA replication tracts were sequentially labeled with CldU (red) and IdU (green). h, Quantification of DNA fiber types. RNaseH1-WT expression reduced the proportion of stalled replication forks in cells harboring BRIP1 R162Q. i, While the overall fork speed was not significantly increased upon RNaseH1-WT expression, tracts displayed a more balanced distribution of CldU and IdU incorporation. j, Fork asymmetry analysis. RNaseH1-WT expression reduced fork asymmetry, indicating that left- and right-moving sister forks progressed at more similar speeds. Labeled tracks were visualized by confocal microscopy, and tract lengths were measured on raw LSM images. Lengths (µm) were converted to replication speed (kb/min) using a factor of 2.59 kb/µm. All data represent mean ± SEM from three independent experiments. At least 150 fibers per condition were analyzed in each replicate. Statistical significance was determined using paired two-tailed Student’s t-test (*p < 0.05, **p < 0.01, ***p < 0.001, ns = not significant). c, e, Representative confocal images are shown.

Article Snippet: For R-loop removal, cells were transiently transfected with an EGFP empty vector control (pEGFP-C1, Takara Bio, #632470), EGFP-tagged RNaseH1 wild-type (WT), or the catalytically inactive RNaseH1 D145N mutant as indicated.

Techniques: Stable Transfection, Expressing, Transfection, Plasmid Preparation, Fluorescence, Western Blot, Construct, Immunofluorescence, Labeling, Confocal Microscopy, Two Tailed Test