Analysis of Residual DSBs in Ataxia-Telangiectasia Lymphoblast Cells Initiating Apoptosis

Figure 2

(a) Cell cycle analysis. The histograms show the cell cycle distribution of normal and AT cells before irradiation and at 24, 48, and 72 hours after irradiation. Cell cycle distribution was obtained by means of PI staining, which measures DNA content. The frequency of cells entering in S-phase for each cell type and each time point is shown, evidencing lack of IR-induced G1 checkpoint arrest in AT cells. The fraction of cells arrested in G2/M after irradiation and the tetraploid population (4N) arising after irradiation have also been highlighted. The frequencies displayed are the mean of two independent experiments in which a minimum number of 10000 cells were analyzed. (b) Tetraploidization and centrosome number. The image shows an AT lymphoblast (probably a metaphase) with 3 pericentrin signals (green; white arrowheads). The DNA is stained with DAPI and the red staining corresponds to α-tubulin. The bars in the graph show the fraction of tetraploid cells scored in AT and normal lymphoblasts before and after irradiation. The values are the mean of two experiments, and the error bars show the standard deviation. The lines in the graph depict the fraction of cells with an abnormal centrosome number (>2) within the same time points. The values for centrosome number were obtained after analyzing a minimal number of 400 cells for each cell type and each time point. The asterisk indicates statistical differences between normal and AT lymphoblasts in the frequency of cells with more than 2 centrosomes ( test; values < 0.002).

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