Figure 4.

SPDL-1 is required for a functional spindle checkpoint and kinetochore localization of Mad2^MDF-2. (A) Perturbation to generate monopolar spindles in the second division and trigger spindle checkpoint activation in C. elegans embryos. ZYG-1 is a kinase required for centriole duplication (O’Connell et al. 2001). In zyg-1(RNAi) embryos, the first division is normal, because two intact centrioles are contributed by sperm that is not affected by RNAi. These centrioles are unable to duplicate, however, resulting in a monopolar spindle in the subsequent division. (B) Average time from NEBD to chromosome decondensation in the P₁ cell of a worm strain expressing GFP:histone H2B. ZYG-1 single depletion results in a significant delay that depends on Mad2^MDF-2, SPDL-1, and ROD-1. Error bars represent the SEM with a 95% confidence interval. A similar result is observed in the AB cell (data not shown). (C) Stills from a time-lapse sequence of the AB cell monopolar division in a worm strain coexpressing GFP:Mad2^MDF-2 and mCherry:histone H2B. In ZYG-1 single depletions, GFP:Mad2^MDF-2 accumulates on kinetochores that are distal to the pole (arrow). Codepletion of ZYG-1 with SPDL-1 or ROD-1 prevents kinetochore accumulation of GFP:Mad2^MDF-2 (see also Supplemental Movie 7). Bar, 5 μm.