Centrosome loss and monopolar spindle formation in haploid HAP1 cells. (A and C) Immunostaining of α-tubulin and chromosomes (stained using DAPI; A), or γ-tubulin and centrin (C) in haploid and diploid mitotic cells. Enlarged images (3×) of centrosomes are shown at bottom in C. (B and D) Frequency of spindle polarities (B) and centrosome or centriole numbers (D) in A and C, respectively. Values represent means ± standard error (SE) of three independent experiments (*, P < 0.05; **, P < 0.01, t test). At least 159 (B) or 302 cells (D) were analyzed per condition. (E) Live images of haploid EGFP-α-tubulin cells taken at 12.5-min intervals. NEBD was set as 0 min. Arrowhead indicates an acentrosomal pole newly formed from a monopolar spindle. Broken lines show cell boundaries. Asterisks mark neighboring cells. (F) Classification of mitotic defects (outer circle) sorted by spindle polarities (inner circle) determined by analysis of 1,264 haploid EGFP-α-tubulin cells from five independent experiments. Cells that moved out of the field of view during the mitotic phase were categorized as unknown.