A balance of kinase and phosphatase activity tunes the extent of expansion. (A–D) Mitotic chromosomes assembled in the indicated nocodazole-treated extract. (E) Mitotic spindles assembled in extracts treated with 1–3 µM PP1 inhibitor I-2 and processed for immunofluorescence against BubR1 (top, white; bottom, magenta). (F) Quantification of BubR1 signal for individual kinetochores, mean, standard deviation, and fold change in black. Mann–Whitney test: ***, P < 0.0001. All images are maximum intensity projections of 3D-SIM datasets; bars, 1 µm. A.U., arbitrary unit.