Functional relationships between PP4c and Cdk1. (A) PP4c dephosphorylates cyclin B1 (top left) and NDEL1 (top right) in vivo. Synchronously growing HeLa cells cotransfected with constructs as indicated above the panels and were costained with the indicated antibodies. Images were captured at G2. To express active Cdk1 in G2, mitotic Cdk1 was used. Mitotic Cdk1 efficiently phosphorylated cyclin B1 and NDEL1 in vivo in G2. These phosphorylations were clearly abolished by the cotransfection of PP4c. The frequency of phosphorylation is summarized at the bottom (one example of three independent experiments; n = 100), and statistical analysis of phosphorylation-positive cells is shown. (B) Expression of mitotic Cdk1 facilitates recruitment of katanin p60 to the centrosome (top left). Synchronously growing HeLa cells were cotransfected with constructs as indicated above the panels and were costained with the indicated antibodies. Images were captured at G2. Expression of mitotic Cdk1 in G2 HeLa cells revealed augmentation of the concentration of katanin p60 at the centrosome (one example of three independent experiments; n = 100). The MT array appeared sparsely distributed in mitotic Cdk1-expressed HeLa cells (right). Statistical analysis of the fluorescence intensity of p60 is shown at the bottom left. Error bars represent SEM. (A and B) Arrowheads indicate centrosomes. *, P < 0.001; **, P < 0.05. Bars, 10 μm.