Fig. 4.

PP1 phosphatases localize to the midbody and depletion of PP1β and MYPT1 causes cytokinesis failure. a–d HeLa cells were fixed and stained to detect to detect DNA (blue in the merged panels), tubulin, and PP1α (a), PP1β (b), PP1γ (c), and MYPT1 (d). For RNAi depletions, HeLa cells were treated with siRNAs directed against each of the three PP1 catalytic subunits or MYPT1 and after 48 h were fixed and stained to detect the same epitopes as described above. DNA condensation and shape and thickness of microtubule bundles at the intercellular bridge were used as criteria to stage telophase cells. Insets show a 3× magnification of the midbody. Scale bars, 10 µm. e HeLa Kyoto cells were treated with siRNAs directed against either a random sequence (control) or each of the three PP1 catalytic subunits (left) or MYPT1 (right) and after 48 h proteins were extracted and analyzed by western blot to detect the indicated proteins. The numbers on the left indicate the sizes in kDa of the molecular mass marker. f HeLa cells were treated with siRNAs directed against either a random sequence (control) or MYPT1 and after 48 h were fixed and stained to detect DNA, tubulin, and di-phosphorylated MRLC. Note that MYPT1 siRNA cells show abnormal cell and nuclear shape, cortical blebs (arrowheads) and disorganized microtubule and actomyosin cytoskeletal filaments. Scale bars, 10 µm. g HeLa cells were treated with siRNAs directed against either a random sequence (control) or MYPT1 and after 48 h were fixed and stained to detect DNA and tubulin. The arrows indicate multinucleate cells. Scale bars, 10 µm. h Quantification of multinucleate cells obtained after siRNA of the three PP1 catalytic subunits or MYPT1. More than 500 cells were counted in n ≥ 3 independent experiments. Bars indicate standard errors. *p < 0.05, **p < 0.01 (Mann–Whitney U test). Source data for Fig. 4e and h are provided as a Source Data file