Ensheathed chromosomes promote formation of micronuclei. (A) Stills from live-cell imaging experiments to track the fate of ensheathed chromosomes. A control or GSK923295-pretreated GFP-Sec61β RPE-1 cell is shown; DNA is stained using SiR-DNA (red). Scale bars, 10 µm; 2 µm (insets). Shown in Videos 5 and 6. (B) Sankey diagram to show the fate (right) of cells in each of the three metaphase classes (left). Fates include normal division, micronucleus formation, death, and other defects (lagging chromosome, cytokinesis failure). Note that the fate of cells (and not chromosomes) is tracked. A cell with three misaligned chromosomes, only one of which is ensheathed, is classified as ensheathed. Parental RPE-1 cells (Parental, n = 92) and untreated RPE-1 stably expressing GFP-Sec61β (Control, n = 69) are from two and three independent overnight experiments, respectively. Fates of GSK923295-pretreated GFP-Sec61β cells (n = 186) were compiled from seven experiments. Fates of individual chromosomes are shown in Fig. S5 B.