Fig. 2. Mixl1^–/– embryos show an accumulation of mesenchymal cells in the thickened primitive streak and adjacent mesoderm. Lateral views of an early-bud stage wild-type (+/+) embryo (A) and a mid-streak stage Mixl1^–/– (–/–) (F) embryo. The Mixl1^–/– embryo has a thickened primitive streak, lacks a node (n) and shows delay in closure of the amnion (paf, posterior amniotic fold). Transverse sections through wild-type (B-E) and Mixl1^–/– (G-J) embryos at the levels indicated in A,F, showing the congregation of cells in the anterior segment of the primitive streak (ps) and adjacent mesoderm (lm) in the mutants. The allantois (al) and chorion (ch) are morphologically similar in the wild type and mutant. Scale bar: 25 µm.