Srs2 promotes abscission inhibition in Topo II–deficient cells. (A) Time-lapse images of representative cells of the indicated genotypes expressing Htb2-mCherry (magenta) and Myo1-GFP (green) to visualize chromatin and the actomyosin ring, respectively. Numbers indicate time (min) relative to the start of ring contraction (t = 0). Scale bar: 2 μm. (B) Box plot showing the time from onset of contractile ring constriction to chromatin bridge segregation in the indicated strains. n = number of cells pooled from two independent experiments. Box indicates median and interquartile range, whiskers are calculated with the Tukey method, and outliers are shown as dots. (C) Membrane ingression and abscission in cells of the indicated genotypes. Time in minutes, 0 min indicates the start of membrane ingression. Yellow arrow marks the position of spindle poles. Asterisk specifies membrane ingression. White arrowhead marks complete separation of the plasma membrane. Time is indicated in minutes; 0 min indicates the start of membrane ingression. Asterisk specifies membrane ingression. White arrowhead marks complete constriction of the plasma membrane (abscission). Single Z-slices are shown, but 12 Z-slices spaced 0.3 μm, spanning the whole cell, were used for image analysis. Lower zoom-in panel shows the dynamics of membrane ingression at the central Z-slice. Scale bar: 5 μm; inset, 2 µm. (D) Fraction of cells that complete abscission from the time of membrane ingression. n = cells pooled from N = 3 independent experiments with similar results. WT vs. top2-4, and top2-4 vs. top2-4 srs2∆, P < 0.0001, Mann–Whitney test. (E) Time course of abscission completion in cells of the indicated genotypes, scored as in D. Data represent the mean ± SD from four independent biological replicates, with 20–30 cells per genotype per replicate. (F) Fraction of cells that completed abscission within 60 min of membrane ingression. Bars represent the mean ± SD from four to six biological replicates (dots), with 20–30 cells per replicate. Statistical analysis was performed using Tukey’s multiple comparisons test; ****P < 0.0001. Ns, nonsignificant, P > 0.05.
Figure 3.

Srs2 promotes abscission inhibition in Topo II–deficient cells. (A) Time-lapse images of representative cells of the indicated genotypes expressing Htb2-mCherry (magenta) and Myo1-GFP (green) to visualize chromatin and the actomyosin ring, respectively. Numbers indicate time (min) relative to the start of ring contraction (t = 0). Scale bar: 2 μm. (B) Box plot showing the time from onset of contractile ring constriction to chromatin bridge segregation in the indicated strains. n = number of cells pooled from two independent experiments. Box indicates median and interquartile range, whiskers are calculated with the Tukey method, and outliers are shown as dots. (C) Membrane ingression and abscission in cells of the indicated genotypes. Time in minutes, 0 min indicates the start of membrane ingression. Yellow arrow marks the position of spindle poles. Asterisk specifies membrane ingression. White arrowhead marks complete separation of the plasma membrane. Time is indicated in minutes; 0 min indicates the start of membrane ingression. Asterisk specifies membrane ingression. White arrowhead marks complete constriction of the plasma membrane (abscission). Single Z-slices are shown, but 12 Z-slices spaced 0.3 μm, spanning the whole cell, were used for image analysis. Lower zoom-in panel shows the dynamics of membrane ingression at the central Z-slice. Scale bar: 5 μm; inset, 2 µm. (D) Fraction of cells that complete abscission from the time of membrane ingression. n = cells pooled from N = 3 independent experiments with similar results. WT vs. top2-4, and top2-4 vs. top2-4 srs2∆, P < 0.0001, Mann–Whitney test. (E) Time course of abscission completion in cells of the indicated genotypes, scored as in D. Data represent the mean ± SD from four independent biological replicates, with 20–30 cells per genotype per replicate. (F) Fraction of cells that completed abscission within 60 min of membrane ingression. Bars represent the mean ± SD from four to six biological replicates (dots), with 20–30 cells per replicate. Statistical analysis was performed using Tukey’s multiple comparisons test; ****P < 0.0001. Ns, nonsignificant, P > 0.05.

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