Ntl synergistically interacts with Ppt and Kny to regulate cell movements in the developing posterior body. At one somite, cells within the posterior tailbud were labeled by uncaging with ultraviolet light and, at 18 somites, the position of the labeled cells was determined (A). The labeled cells (red) are within the mesendoderm and lateral to the notochord (ntl in blue) in the wild-type embryos (B,b) and slb mutants (C,c). In ntl mutants (D,d), labeled cells are also within the mesendoderm (D) but are positioned medially (d). In ppt mutants (E,e), the cells occupy the mesendoderm (E) and are lateral to the notochord (e). In kny mutants, cells are within the mesendoderm (F) and lateral to the notochord (f). In ppt;ntl (G,g) and kny;ntl (H,h) mutants, labeled cells are present in both the mesendoderm and ectoderm and fail to move from the posterior bud laterally or to extend (g,h). (B-H) Lateral views. The ntl mutant cells transplanted into wild-type embryos undergo subduction and lateral divergence (I,i). (b-h,I,i) Dorsal posterior views. Scale bar=100 μm.