plst-1 null zygotes display defects in cortical contractility-related processes during early embryogenesis. (A) Schematic showing position of the tm4255 deletion in the plst-1 gene and its possible truncated protein product. CH, calponin homology domain; EF, EF-hand like domain. (B) RT-PCR analysis of plst-1 mRNA in control and plst-1(tm4255) worms shows that no message can be detected in the mutant. (C) Equatorial view of control and plst-1 zygotes expressing membrane marker GFP::PLC1δ-PH and histone marker HIS-58::mCherry. Yellow, red, and cyan arrowheads highlight cortical ruffling, pseudocleavage, and membrane invaginations, respectively. (D) Quantification of maximum pseudocleavage ingression in control (n = 13) and plst-1 (n = 18) zygotes. (E) Quantification of pronuclear meeting position along the anterior–posterior (AP) axis in control (n = 16) and plst-1 (n = 19) zygotes. Dotted line represents medial position (i.e., 0.5) along the A-P axis. (F) Quantification of the number of membrane invaginations in the anterior and posterior cortex of the control (n = 13) and plst-1 (n = 20) zygotes from anaphase onset to cytokinesis completion. (G) Montages of the posterior cortex in control and plst-1 zygotes expressing mCherry::PLC1δ-PH and GFP::tubulin during spindle oscillation. Asterisks indicate sites of membrane invaginations. Representative line scan of mCherry::PLC1δ-PH and GFP::tubulin signals in the plst-1 montage are shown on the right. (H) Cortical view of control and plst-1 zygotes expressing NMY-2::GFP with laser ablation being performed at the anterior cortex. White line depicts site of ablation. (I) Superimposed images of NMY-2::GFP before (magenta, −5 s) and after (green, +5 s) cortical laser ablation (0 s) in control and plst-1 zygotes. White line depicts site of ablation. (J) Quantification of initial outward velocity after cortical laser ablation in control (n = 19) and plst-1 (n = 20) zygotes. Data are represented as mean ± SEM. ****, P < 0.0001; *, P < 0.05; Mann–Whitney U test. Bars, 5 µm.