Abnormal CB membrane domains in how18 and dg62 mutant embryos. (A–F) Transverse Z views of CBs from how18 mutant embryos at different stages of development (from stages 14–16) stained for Arm (red) and Dg (green). (A′–F′ and A″–F″) The same views showing staining for Arm or Dg only. Arm expression is spread toward the ventral side of the CBs, colocalizing partially with Dg (A′, B′, A″, and B″). Notice that CBs do not change their shape or constrict; they behave similarly to what is observed in slit² mutant embryos. (G–L) Transverse Z views of CBs from dg62 mutant embryos stained for Arm (red) and for Trol (D. melanogaster perlecan, green). (G′–L′ and G″–L″) The same views as G–L, showing Arm or Trol staining only. dg mutant CBs do not change their shape (G″–L″) and resemble how mutant CBs. The dorsal J domain is enlarged compared with the wild type (H′ and J′–L′ [arrowheads], compared with Fig. 4 G′) and overlaps with the Trol-positive L domains. (M) Diagram summarizing the observations in how18 and dg62 mutant embryos. Compare the extension and localization of J and L domains with wild-type embryos (Fig. 4 K). Arrowheads show the dorsal J domain expressing Arm. Bars, 4 μm.