Pk2 changes the organization of the actomyosin network at TCJs. (A and B) Representative images of Sf9-mNeon and Scarlet-UtrCH in the control (A) or Flag-Pk2–expressing (B) gastrula ectoderm. Imaging was initiated at stage 11. The square areas in A and B are enlarged in a, b, and b′. The arrows represent NMII puncta formed near the center of the F-actin puncta in tricellular vertices in the wild-type ectoderm. The arrowheads in b and b′ represent split NMII puncta in the Pk2-overexpressing ectoderm. Schematics are shown in the right panel. Note that some NMII puncta are in the peripheral region of tricellular vertices. (C) Number of NMII puncta in individual vertices. Vertices consisting of three cells were used for quantification. Images of sf9-mNeon were processed with a threshold mask (>300 fluorescence intensity). The number of identifiable sf9-mNeonGreen puncta near TCJs was counted. The chi-square test. P < 0.001. Three embryos per group were used. The total number of TCJs was as follows: n = 206 (control) and n = 179 (+Pk2 OE). (D and E) Quantification of Sf9-mNeonGreen (D) and Scarlet-UtrCH (E) fluorescence intensity at TCJs. After segmentation, the mean fluorescence intensities were measured via dilated masks of pixels that defined TCJs (five pixels [0.76155 μm] in diameter). The Mann‒Whitney U test was used to compare mean ranks. Three embryos per group were used. The total number of TCJs was as follows: n = 243 (control) and n = 195 (+Flag-Pk2). *P < 0.05; **P < 0.01, ***P < 0.001. Scale bars: 20 μm (A and B) and 5 μm (a–b′).