Cortical contractility restricts centrosome movement to promote HSET-mediated centrosome clustering. (A) Representation of live 3D measurements of distances between pairs of clustering centrosomes in MCF10A and MCF10A CDH1^−/− cells. Green and red lines represent the centrosomes’ trajectories during the eight time points (every 40 s) before and after the image shown, respectively. d1 and d2 represent centrosome distance. (B) Graphic depicting centrosome distance, d, over time for each successfully clustering pair (WT, n = 31; CDH1^−/−, n = 40). Cluster completion was defined as the time point at which separation stabilized. (C) Population mean square displacement of centrosome separation during centrosome clustering (WT, n = 31; CDH1^−/−, n = 40). The vertical dashed line represents the transition between search-and-capture and motorized clustering phases. (D) Histograms of centrosome separation, d, during the search-and-capture phase of centrosome clustering, as seen in the schematic. Data are for centrosome pairs that successfully cluster (WT, n = 155; CDH1^−/−, n = 102), and centrosome pairs that fail to cluster in cells that also contain a successful cluster event (WT, n = 683; CDH1^−/−, n = 718). Values given are medians ± SEM. (E) Centrosome distance for each pair that fail to cluster (CDH1^−/− siRNA ctr, n = 70; CDH1^−/− siRNA HSET, n = 115; WT siRNA HSET, n = 141). Trajectories are aligned at anaphase onset. (F) The population mean (top) and SD (bottom) of nonclustered centrosome pairs in F, demonstrating the increased variability (SD) in d after loss of HSET, and further with inhibited cortical contractility. The vertical dashed line represents the anaphase B onset. (G) Schematic representation explaining the biphasic model for centrosome clustering. Bars, 10 µM.