Fig. 5.

Interplay of Parp-1 and SirT1 in the architecture of the nucleolus. A Representative immunofluorescence images for the immunodetection of the nucleolar marker B23 (red) in Parp-1^+/+;SirT1^+/+ (a), Parp-1^+/+;SirT1^−/− (b), Parp-1^+/−;SirT1^−/− (c) and Parp-1^−/−;SirT1^−/− (d) cells counterstained with DAPI (blue, e–h). The absence of SirT1 results in nucleoli fragmentation as shown by the numerous B23 marked subnuclear structures (b). In contrast only few nucleoli (<10) are counted in Parp-1^+/+;SirT1^+/+ (a), Parp-1^+/−;SirT1^−/− (c) and Parp-1^−/−;SirT1^−/− (d) cells. B Histogram showing the percentage of cells with a normal number of nucleolar foci (<10) or multiple nucleolar foci (>10). Mean values (±SD) are indicated. Of note, around 20% of the Parp-1^−/−;SirT1^−/− cells displayed a normal number but irregularly-shaped nucleoli. A total average of 500 cells were scored per cell line in >20 randomly selected immunofluorescence fields. P value was calculated by ANOVA test: **P < 0.01, ***P < 0.001. C Transient transfection of Parp-1^+/+;SirT1^−/− cells with wild-type SirT1 (green, b, e) restores nucleolus integrity marked by B23 (red, c) and relocalization of HP1α onto pericentric heterochromatin (red, f) when compared to an untransfected cell. DNA and heterochromatic foci are counterstained with DAPI (a, d). Scale bars 7 µm