Microtubule-binding mutants of KNL-1 significantly extend the spindle checkpoint–mediated cell cycle delay induced by monopolar spindles. (A) A schematic of the monopolar spindle–based checkpoint signaling assay in C. elegans embryos. Depletion of the centrosome duplication kinase ZYG-1 generates monopolar spindles in the second division, which trigger a spindle checkpoint–dependent cell cycle delay. (B) Mean time from NEBD to chromosome decondensation in the AB cell for the indicated conditions. Error bars represent the SEM with a 95% confidence interval. The gray dashed line marks the duration of AB cell mitosis for the WT transgene, and the red dashed line marks the duration of AB cell mitosis induced by monopolar spindles in the same strain. For comprehensive statistical analysis, see Table S2. (C) Stills from time-lapse sequences of the AB cell monopolar division in worm strains coexpressing GFP::Mad2^MDF-2 and the indicated transgenes. Mad2^MDF-2 accumulation on unattached kinetochores is marked with open arrowheads. Bar, 3 µm.