Examination of cell junction markers. All embryos are stage 17. (A) E-Cad localizes to CB apical surfaces (arrow). (B) In slit GOF embryos, E-Cad is also localized to CB basal surfaces (arrow). (C) In robo mutants, E-Cad accumulates at high levels at CB apical domains. (D) EM of an ena mutant. Arrow indicates a region where CBs fail to make contact. (E and F) E-Cad staining in cross-sectioned embryos as visualized by HRP staining. (E) in slit GOF embryos, E-Cad is enriched at sites of cell contact in both lumens (arrowheads). (F) In robo mutants, E-Cad accumulates at apical domains where CBs remain in contact (arrow). (G–I) Mef2 (magenta) and Ena (green), which concentrates at CB apical surfaces (arrow) in wild-type embryos (G). In slit GOF embryos (H), Ena is mislocalized to CB basal and lateral domains in discrete puncta (arrows). (I) In robo mutants, Ena is no longer concentrated at the apical domain of CBs. (J–L) Same as G–I showing Ena alone. Bar, 1 μm.