Cell segregation relies on kinase-dependent signaling through EphB receptors. E8.5 Efnb1^ΔXGFP/+ mouse embryos with analog-sensitive kinase mutations in EphB1, EphB2, and EphB3 (Ephb^{AS-TKI/AS-TKI}) or WT EphBs (Ephb^+/+), treated with vehicle or 1-NA-PP1. Numbers of embryos analyzed are presented in Table S2. The GFP signal was adjusted in a nonlinear fashion to assist discrimination of the ephrin-B1–negative population. Bars, 100 µm.