Fig. 4: Dermal Kaposi’s sarcoma tumours show features of ALT activity.

a Representative overview of dermal KS biopsy section. Micrograph shows DAPI nuclear counterstain in grey, autofluorescence of erythrocytes and extracellular matrix of tissue is visible in red (Cy3) for illustrative purposes. b Quantification of mean telomere signal intensity. Telomere FISH signals from every tumour cell nucleus and bystander epidermal cell within the same section were quantified, majority of cases > 1000, derived from at least 100 cells per condition. Each dot represents a distinct patient, n > 20. Statistical significance was tested with paired Wilcoxon signed-rank test (****p < 0.0001). c Quantification of variance of data obtained by mean signal intensity measurements. Coefficient of variance was determined for each cell type and plotted, analysis outcome and smaple size as in b. d Plot showing correlation of measurements presented in b, c. Correlation was deteremined with Pearson’s correlation coefficient (PCC). Line of best fit generated by linear regression (slope = PCC value). e Representative IHC/FISH image of spindle cells showing LANA and PML IHC staining and telomere FISH signals used for analysis in b–d generated by maximum intensity projection in Z of confocal micrographs. f Comparative quantification of proportion of cells with APBs (1/3 PML bodies at telomeres) for tumour cells and epidermal bystander cells within the same tissue section. Significance tested by paired Wilcoxon signed-rank test (n > 20, ***p = 0.0008). g Representative image generated in same manner as described for e, except for IHC was performed for pRPA (S33) instead of PML. h Quantification of cells with pRPA TIFs (at least one co-localisation event) for same cell types as in f (n > 20, **p = 0.0013). i Representative southern blot image of C-circle analysis. Slot blots were hybridised with probes specific to telomeres (top row) and Alu repeat for loading control (bottom row). j Quantification of C-circles in primary tumour material normalised to loading control. Each dot represents one patient or healthy skin donor, n > 20 each. Significance tested by unpaired, two-tailed t-test (**p = 0.0026).