PLST-1 is required for long-range directional cortical flows and robust polarization of the zygote. (A) Representative kymographs of GFP::Utrophin and NMY-2::GFP in control and plst-1 zygotes during polarity establishment and maintenance. (B) Mean vector field of NMY-2::mCherry cortical flow in the control (n = 6) and plst-1 (n = 5) cortex during polarity establishment, based on PIV analysis. (C) X-component velocity profiles of NMY-2::mCherry cortical flow in control (n = 15) and plst-1 (n = 14) zygotes during polarity establishment. (D) Decay profile of cosine similarity between 2 vectors in the NMY-2:mCherry cortical flow in control (n = 15) and plst-1 zygotes (n = 14) during polarity establishment. (E) Cosine similarity length of control (n = 15) and plst-1 (n = 14) zygotes during polarity establishment. Data are represented as mean ± SEM. ****, P < 0.0001, by Mann–Whitney U test. (F) Equatorial view of control, plst-1 mild, and plst-1 severe zygotes expressing mCherry::PAR-6 and GFP::PAR-2. Bars, 5 µm. (G) Representative kymographs of linearized plasma membrane of control, plst-1 mild, and plst-1 severe zygotes expressing mCherry::PAR-6 and GFP::PAR-2. (H) Polarity indices of mCherry::PAR-6 and GFP::PAR-2 in control (n = 12), plst-1 mild (n = 10), and plst-1 severe (n = 4) zygotes with time zeroed at pronuclear meeting. The polarity index was calculated by dividing the fluorescence intensity of each PAR protein in its respective domain by its intensity in the entire cortex. Data are represented as mean ± SEM.