Journal: The Journal of Biological Chemistry
Article Title: DNA-damage dependent isoform switching modulates RIF1 DNA repair complex assembly and phase separation
doi: 10.1016/j.jbc.2025.110857
Figure Lengend Snippet: The S/K cassette stabilizes phase separation of the RIF1 CTD. A , predictive disorder score of GFP-RIF1 CTD -S and GFP-RIF1 CTD -L showed that the presence of S/K cassette (2250–2275 amino acids) decreases the disorder of RIF1 CTD. B , ( left panel ) representative examples of RIF1 CTD anisosomes. U-2 OS cells were transiently transfected with GFP, GFP-RIF1 CTD -L ΔNLS , GFP-RIF1 CTD -S, or GFP-RIF1 CTD -L and subjected to live cell imaging after Hoechst 33342 staining ( blue ). B , ( right panel ) quantification of the mean anisosome area ± standard error by customized ImageJ script. Each dot represents an anisosome scored, n = 586 for GFP-RIF1 CTD -S; n = 396 for GFP-RIF1 CTD -L for the total number of anisosomes. The p -value from unpaired two-tailed t - test assuming equal standard deviation was shown. C , timelapse images and the schematic showing the fusion of GFP-RIF1 CTD anisosomes in 60 s. Single anisosomes and the subsequently fused multichambers anisosomes were marked with white arrows . D , full-length GFP-RIF1-S occasionally forms anisosome-like structure in Dox-inducible RIF1 −/− U-2 OS cells. Scale bar = 10 μm. E , in vitro phase separation assays showed concentration (10–40 μM)-dependent LLPS droplet formation of purified GST-RIF1 CTD -S and GST-RIF1 CTD -L proteins. Scale bar = 10 μm. F , fluorescence recovery after photobleaching (FRAP) montage for representative GFP-RIF1 CTD -S and GFP-RIF1 CTD -L anisosomes in U-2 OS cells. Morphological distinct anisosome structures—“Solid ball” and “Donut”—were depicted. Scale bar = 1 μm. G , H , FRAP recovery curves of the bleached anisosomes for GFP-RIF1 CTD -S and GFP-RIF1 CTD -L over a time course of 3 minutes. Four biological replicates were carried out, each with at least three technical replicates. Each recovery curve was color-coded according to the biological replicate number (S1-4 or L1-4) in each plot . I , J , each recovery curve from ( G ) and ( H ) was fitted by single exponential equation to estimate the t-half value of recovery and mobile fraction of the anisosome. Bar height represents mean ± standard error of the pooled data. Each dot represents score from an anisosome, n = 21 for GFP-RIF1 CTD -S and n = 22 for GFP-RIF1 CTD -L. The p -values from unpaired two-tailed t -tests with Welch’s correction which do not assume equal standard deviation in populations were listed. K , L , manual tabulation of the recovery frame where the two distinct stages—“solid ball” and “donut”, as indicated in ( F )—reappeared after photobleaching was done. Bar height represents mean ± standard error of the pooled data. Each dot represents score from an anisosome, n = 21 for GFP-RIF1 CTD -S and n = 22 for GFP-RIF1 CTD -L. The p -values from unpaired two-tailed t -tests with Welch’s correction were shown. M , representative images showed that serine to alanine (SA) and serine to aspartic acid (SD) mutations impede anisosome formation to a greater extent in GFP-RIF1 CTD -S expressing cells. Red boxes showed enlargement of the anisosomes of interest. Scale bar = 10 μm. CTD, carboxyl-terminal domain; GFP, green fluorescent protein; GST, glutathione-S-transferase; LLPS, liquid–liquid phase separation; RIF1, RAP1 interacting factor 1; RIF1-L, RIF1-Long; RIF1-S, RIF1-Short; S/K cassette, Ser/Lys-rich cassette.
Article Snippet: Nuclear DNA was either stained with 0.5 μg/ml DAPI for 10 min at room temperature and then mounted with mounting medium for fluorescence (Vector, H-1000) or directly mounted in mounting medium with DAPI for fluorescence (Vector, H-1200) before imaging.
Techniques: Transfection, Live Cell Imaging, Staining, Two Tailed Test, Standard Deviation, In Vitro, Concentration Assay, Purification, Fluorescence, Expressing