TIF formation in HHS-affected fibroblasts with normal telomere length.
(A) Control (C) and HHS-affected (S2) primary fibroblast cultures (established at the ages of 30 and 17 years, and grown to PDL of 14 and 10, respectively) were immunostained for TRF1 (green) and γ-H2AX (red), and with DAPI for the nuclei (blue), as indicated above the images. The bottom panels show enlarged images that include several telomeres. The images of the affected and control cells were obtained and processed in the same way, side by side. (B) The number of TIFs (defined as colocalized TRF1 and γ-H2AX foci) was counted in randomly-chosen 67 affected and 58 control cells. The graph shows the percentage of cells with at least five such foci. (C) Genomic DNA was prepared from these cultures and the average length of telomeres estimated by Southern analysis.