B. TEM analysis of SPBs. PHSL1-CDC20 ama1∆ cdc28-as2 cells were treated with 1Na-PP1 at 3 h in SPM. At 9 h in SPM, cells were washed with cSPM containing (top) or lacking 1Na-PP1 (washout, bottom). TEM samples were collected at 13 h in SPM. Washout of 1Na-PP1 causes MP formation (P < 0.0001, Fisher's exact test). Scale bar, 0.2 μm. 