STR is required for Pk2-mediated inhibition of cell packing. (A) Scheme of Pk2 deletion mutant constructs. Pk2 contains one PET, three LIM domains, intrinsically disordered regions (IDRs), and a CAAX motif. The IDRs include three conserved regions: the STR, the VBD, and the C4 region between the STR and VBD. (B–G) Representative images of stage 11 ectoderms expressing myrGFP only (B) or myrGFP with Pk2 deletion mutants (C–G). Albino embryos were used to visualize the lateral domain. (H–J) Tissue fluidity was evaluated by scoring AJ linearity (H), AJ length distribution (I), and the number of neighboring cells (J). Pigmented wild-type embryos were used for quantification. AJ linearity was quantified as described in Fig. 3 H. Individual dots represent the average AJ linearity in one embryo, and lines represent the average linearity of three embryos in H. Original numerical data were used in H and I. One-way ANOVA was used to compare mean ranks, with the Bonferroni correction for multiple pairwise comparisons in H. The Kolmogorov‒Smirnov test was used to compare distributions in I. The chi-square test was used in J. Three embryos per group were used. The total number of cells and AJs was as follows: 308 cells and 1,050 AJs (myrGFP); 517 cells and 1,722 AJs (+Pk2); 296 cells and 1,019 AJs (+Pk2ΔSTR); 396 cells and 1,366 AJs (+Pk2ΔC4); 334 cells and 1,151 AJs (+Pk2ΔVBD); 378 cells and 1,272 AJs (+Pk2ΔC30). *P < 0.05, **P < 0.01, ***P < 0.001, n.s., not significant. Scale bars: 10 μm.