Fig. 1. Pleiotropic Notch defects in Mib1^–/– embryos. (A,B) Wild-type (A) and Mib1^–/– (B) embryos at E9.0. The wild-type embryo has the first and second branchial arches (A, arrows), while the Mib1^–/– embryo only has the first branchial arch (B, arrow) with a distended pericardial sac (asterisk) and small, irregular somites (arrowheads). (C-F) Vascular defects in the yolk sac of E9.5 Mib1^–/– embryos (D,F), as compared with the wild type (C,E). The blood vessels are indicated (asterisks). (G,H) Transverse sections of wild-type (G) and Mib1^–/– (H) embryos at E9.5. The Mib1^–/– embryo has a smaller dorsal aorta (da; inset i), a thinner neural tube (nt), loss of mesenchymal cells (asterisk), an enlarged pericardial cavity (#) and a fused notochord (inset ii). (I,J) Transverse section of wild-type (I) and coronal section of Mib1^–/– (J) embryos at E9.5. A kinked neural tube (asterisk) and irregular somites (arrows) are evident in the Mib1^–/– embryo (K) Myogenin expression (bracket) in E9.5 wild-type (left) and Mib1^–/– (right) embryos. (L-P) Expression of Uncx4.1 (L), Dll1 (M), Hes7 (N), lunatic fringe (Lfng) (O) and Heyl (P) in E8.5 wild-type (left) and Mib1^–/– (right) embryos. The Mib1^–/– embryos lack the characteristic expression of Uncx4.1 (L, arrows), Dll1 (M, arrows and inset), Hes7 (M, arrow and bracket), Lfng (O, arrow and bracket) and Heyl (P, arrow and inset).