LET-99 is required for asymmetry of net spindle positioning forces. (A–C) Analysis of spindle pole movements over time in control and laser-severed spindles for representative wild-type (A), let-99 (B), and par-1 (C) embryos. Top panels for control and severed embryos show spindle pole positions (left y axis, percentage of embryo length) and pole–pole distance (right y axis) plotted against time (x axis). NEB = 0 s. Bottom panels for control and severed embryos show overall spindle pole velocities (left y axis) plotted against time (x axis); the right y axis indicates pole–pole distance. Arrows indicate the time of spindle severing in laser-ablated spindles. (D) Mean spindle pole peak velocities along the AP axis in control (C) and laser-severed spindles (S). Error bars show SEM, lines between columns indicate significance at P = 0.05.