Table I.
Mutations in spn-2 cause defects in nuclear and spindle positioning
| Genotype and conditions | P0 spindle transversea | Ectopic cleavage furrowsb | Mispositioned AB or P1 nucleic | Abnormal AB or P1 spindle positiond |
| Wild type filmed at 23–24C° | 0/10 (0%) | 0/10 (0%) | 0/10 (0%) | 0/10 (0%) |
| spn-2(it149) filmed at 23–24°C | 1/23 (4%) | 14/23 (61%) | 13/22 (59%) | 10/22 (45%) |
| spn-2(it149) filmed > 25°C | 3/13 (23%) | 12/12 (100%) | 11/11 (100%) | 7/10 (70%) |
| spn-2(it149) shifted to 25°C; filmed at 23–24°C | 11/31 (35%) | 24/27 (89%) | 13/22 (59%) | 10/20 (50%) |
| spn-2(it149);mei-1(RNAi) shifted to 25°C; filmed at 23–24°C | 0/17 (0%) | 6/19 (32%) | 3/20 (15%) | 5/20 (25%) |
| F56F3.1(RNAi) filmed at 23–24°C | 5/19 (26%) | 12/19 (63%) | 11/18 (61%) | 12/17 (71%) |
Hermaphrodites were raised at 20°C and shifted to 25°C for 1–2 h if indicated. Embryos were scored using DIC microscopy during the first two divisions, but those with a transverse P0 spindle, cytokinesis defects, or osmosensitivity were excluded from the analysis of AB and P1 defects.
The spindle was positioned at a >45° angle relative to the A-P axis of 0° at either metaphase or anaphase. Of the 20 embryos with this phenotype, 17 failed to center and rotate, but then the spindle became normally aligned by anaphase in 11 of those. The remaining three centered and rotated but the spindle moved to a posterior transverse position during metaphase/anaphase.
More than two ingressing cleavage furrows during and just after cytokinesis.
Nuclei were not centrally positioned after cytokinesis.
The AB spindle aligned within 45° of the A-P axis and/or the P1 spindle was transverse to the A-P axis; in wild type, AB spindles are transverse and P1 spindles are aligned.