STR is responsible for the inhibition of cell packing by Pk2. (A) Schematic diagrams of the Pk1-Pk2 chimeric constructs. (B–H) Representative images of stage 11.5 ectoderms expressing myrGFP only (B), HA-Pk1 (C), Flag-Pk1NPk2C (D), HA-Pk1(2STR) (E), Flag-Pk2 (F), HA-Pk2NPk1C (G), and Flag-Pk2(1STR) (H). Albino embryos were used for imaging. Wild-type pigmented embryos were used for segmentation and quantification. (I–K) Cell packing was evaluated by scoring AJ linearity (I), AJ length distribution (J), and the number of neighboring cells (K). Three embryos per group were used. Original numerical data were used for statistical analyses in I and J. One-way ANOVA was used to compare the mean ranks, with the Bonferroni correction for multiple pairwise comparisons in I. The two-sample Kolmogorov‒Smirnov test was used to compare distributions in J. The chi-square test was used in K. The total number of cells and AJs was as follows: 284 cells and 966 AJs (myrGFP only); 221 cells and 783 AJs (+Pk1); 189 cells and 646 AJs (+Pk1N-Pk2C); 253 cells and 761 AJs (+Pk1(2STR)); 206 cells and 702 AJs (+Pk2); 186 cells and 596 AJs (+Pk2N-Pk1C); 169 cells and 1,228 AJs (+Pk2(1STR)). *P < 0.05, **P < 0.01, ***P < 0.001, n.s., not significant. Scale bars: 20 μm.