Cell segregation in vivo is disrupted by lack of actomyosin contractility. (A) Immunostaining of embryonic day 13.5 coronal sections for EPHRIN-B1 (magenta) and GFP (green) shows segregation in EfnB1^loxXGFP/+;Shox2^IresCre/+ embryos and diminished segregation when actomyosin contractility is disrupted in EfnB1^loxXGFP/+;Shox2^IresCre/+;NMIIA^lox/lox;NMIIB^lox/lox embryos. Scale bar, 50 µm. (B) Distribution of the percentage of XGFP⁺ patches of various sizes. Column height represents means of the distributions across all sections measured for a given genotype; error bars represent SEM. (C) Patch sizes represented as scatterplots. Horizontal bars represent means, and error bars represent SEM. ****, P < 0.0001.