A. DIC time-lapse images of wild-type, zyg-1(or278 ts), zyg-1(or297 ts), zyg-1(or409 ts), and zyg-1(or1018 ts) embryos. In the zyg-1 mutants the two cell stage blastomeres assembled monopolar spindles, cytokinesis failed, and there were multiple nuclei present at the four cell equivilent stage. The zyg-1(or278 ts), zyg-1(or409 ts), and zyg-1(or1018 ts) embryos were obtained from hermaphrodites shifted to the restrictive temperature for 5–6 hours. The zyg-1(or297 ts) embryo was obtained from a hermaphrodite shifted to the restrictive temperature for 30 minutes prior to imaging. Black arrows indicate normal bipolar spindles in the wild-type embryo and white arrowheads indicate multiple nuclei present at the four cell equivalent stage. Times in min:sec are given relative to AB nuclear envelope breakdown (NEBD). Scale bar, 10 µm. B. Amino acid alterations in the mutants. Asterisks indicate the changed residues. Homologous proteins are aligned below the C. elegans protein. C. Defect maps for the zyg-1 mutants.Individual embryos observed during time-lapse recordings: embryos are listed on the left and phenotypes are listed on the top: 1; normal two cell embryo, 2; bipolar spindles at two cell stage, 3; one nucleus per cell at four cell stage. In the long upshifts, hermaphrodites were transferred to the restrictive temperature for 5–8 hours. In the short upshifts, embryos were harvested from hermaphrodites grown at the restrictive temperature for 30 minutes.