Uniform Pk2 promotes AP elongation in NE cells. (A) GFP-Pk2 distribution (high) in stage 15–16 NEs with Scarlet-UtrCH as an AJ marker. (B) Scheme of the experiments for Fig. 9 and Fig. 10. Lifeact-GFP RNA was coinjected with HA-Pk1, Flag-Pk2, or HA-Pk1 (2STR) RNA into one dorsal-animal blastomere (green) at the four- to eight-cell stage. Scarlet-UtrCH RNA was injected into the other dorsal-animal blastomere (red) as a control. The posterior NE close to the border between the brain and the spinal cord was imaged. (C–E) Representative images of NEs expressing Lifeact-GFP with Flag-Pk2 (C), HA-Pk1 (D), or HA-Pk1(2STR) (E) from Video 10. Arrowheads indicate the presumable midline of the embryos. (F–H) Frequency distribution histogram of cell orientation in the NE. The control and Pk-OE sides of the NE were compared in the same time-lapse imaging field. Average and ±S.D. are shown. The Kolmogorov‒Smirnov test was conducted to compare distributions, using original numerical data. Four embryos per group were used. The total number of cells was as follows: n = 403 (control) and 562 (Flag-Pk2 (high)) (G); n = 367 (control) and 350 (HA-Pk1) (H); and n = 484 (control) and 528 (HA-Pk1 (2STR)). Scale bars: 20 μm. *P < 0.05. n.s., not significant.