Fig. 4. Wnt1 cells grafted in place of neural tube and notochord inhibit Sim1 and trigger both Wnt11 and En1 expression in the medial dermomyotome. (A) A fragment of neural tube (NT) plus notochord (NC) was excised at HH13 between somite X (SX) and the chordoneural hinge (arrows). Wnt1 cell aggregates were grafted from somite V (SV) to the unsegmented presomitic mesoderm (PSM) in a length equivalent to five presumptive somites (red arrowheads), in order to maintain two excised ungrafted regions as controls. Embryos were fixed 12 hours (B-D), 24 hours (E-F) or 48 hours (G-J) after the operation. Dorsal views and corresponding transversal section, hybridized with Sim1 (B-D), MyoD (E, F), Wnt11 (G, H) and En1 (I, J) probes. (B-D) Sim1 expression expanded medially in excised ungrafted regions (B,C), while its normal lateral domain of expression was restored around the Wnt1 cell aggregate (asterisk) (B,D). (E,F) MyoD was expressed on both sides of the Wnt1 cell aggregate, in a deep position (F). (G,H) Wnt11 was activated on both sides of the Wnt1 cell aggregate (asterisk) in superficial epithelial structures reminiscent of the dorsomedial lip (H). (I,J) En1 was detected around the graft, in an intermediate mesenchymal population (J). Scale bars: 50 µm.