Reduced spindle tension and efficiency of chromosome alignment in the absence of NuMA. (A) Distance between sister kinetochores in cells arrested in metaphase with MG132 and incubated on ice for 10 min to selectively depolymerize nonkinetochore fiber microtubules. Images represent maximum intensity projections of a deconvolved series of z sections spanning the entire cell in 0.2-µm intervals (projection) or single deconvolved z sections. Kinetochore pairs were identified in single z sections by the relative positioning of kinetochores and orientation of associated kinetochore fibers. Blue, DNA; green, microtubules; red, kinetochores. Bars: (left) 5 µm; and (right) 2.5 µm. (B) Interkinetochore distances of paired sister chromatids in NuMA^+/Δ22, NuMA^Δ22/Δ22, and nocodazole (Noc)-treated control cells. The boxes represent the interquartile (middle 50%), and the whiskers represent the full range. Horizontal lines represent the median value. (C) Examples of NuMA^+/Δ22 cells with fully aligned chromosomes and NuMA^Δ22/Δ22 fibroblasts with chromosome alignment defects. Cells were treated as in A and processed for immunofluorescence to visualize DNA (purple) and tubulin (green). Bars, 5 µm. (D) Percentage of spindles showing chromosome alignments defects. ***, P < 0.0001. Error bars indicate SEM.