Rescue experiments in PP4c-disrupted MEF cells by a Cdk1 inhibitor, additional disruption of Ndel1, and siRNA against katanin p60. (A) Depletion of Cdk1 by siRNA rescued the defect of MTs in PP4c^−/− MEF cells (type A). (left) MT array was rescued by the depletion of Cdk1. (middle) T219 phosphorylation of NDEL1 (left) and katanin p60 distribution (right) under control siRNA or Cdk1 siRNA in PP4c^−/− MEF cells (RFP-Cre positive). One example of three independent experiments is shown. (right) Statistical analysis of the effect of Cdk1 inhibition on MT defects (n = 200 for each of PP4c^cko/cko; control siRNA, PP4c^cko/cko; Cdk1 siRNA, PP4c^−/−; control siRNA, and PP4c^−/−; Cdk1 siRNA). (B) Ndel1 deletion can rescue the defect of MTs in PP4c^−/− MEF cells (type A). (left) PP4c^−/−/Ndel1^−/− MEF cells show a normal MT array compared with PP4c^−/−/Ndel1^+/+ MEF cells. (middle) S123 phosphorylation of cyclin B1 (left) and katanin p60 distribution (right) in PP4c^cko/cko/Ndel1^cko/cko MEF cells (RFP-Cre negative) or PP4c^−/−/Ndel1^−/− MEF cells (RFP-Cre positive). One example of three independent experiments is shown. (right) Statistical analysis of the effect of Ndel1 deletion on MT abnormality (n = 100 for each of PP4c^cko/cko/Ndel1^cko/cko, PP4c^−/−/Ndel1^+/+, PP4c^+/+/Ndel1^−/−, and PP4c^−/−/Ndel1^−/−). (C) Rescue experiments with siRNA against katanin p60 in PP4c^−/− MEF cells (type A). (left) Depletion of katanin p60–rescued MT defects in PP4c^−/− MEF cells. (middle) Depletion of katanin p60 did not prevent the aberrant NDEL1 phosphorylation (left) and the unscheduled cyclin B1 phosphorylation (right) in PP4c^−/− MEF cells (RFP-Cre positive). One example of three independent experiments is shown. (right) Statistical analysis of the effect of katanin p60 depletion by siRNA against katanin p60 on MT defects (n = 200 each of Cre⁻/ctrlRNAi⁺, CRE⁺/ctrlRNAi⁺, CRE⁻/p60RNAi⁺, and CRE⁺/p60RNAi⁺). (A–C) Arrowheads indicate the positions of centrosomes. Bars, 20 μm.