Fig. 1

Fig. 1 TOPdGFP expression reflects known domains of Wnt/β-catenin signaling. Animal pole views are shown in (A) and (B). Lateral views are shown in (C–F), with ventral to the left in (C) and anterior to the left in (D–F). (A) At dome stage (4 hpf), expression is localized to deep marginal cells on one side of the embryo, (arrowhead). (B) By shield stage, expression is observed in the ventrolateral marginal region and in the shield hypoblast (arrowhead). (C) At 80% epiboly, GFP expression expands throughout the ventral mesoderm (vm). (D) Following gastrulation, mRNA is enriched at the posterior (right) end of the embryo. (Inset) Tailbud view shows exclusion of mRNA in the notochord (top). (E) At the six-somite stage, the first expression in the nervous system is seen at the presumptive midbrain/hindbrain boundary (mhb) and hindbrain, with an obvious gap between these regions. (F) By 18 somites, strong GFP expression is present in the midbrain region, with weaker expression in the ventral forebrain and tail mesoderm (tm). Lines indicate planes of section in (G–I). (G) Longitudinal section at 18 somites, showing expression throughout the hindbrain and medial neural crest cells (arrowheads). (H) Transverse section through the hindbrain, with medial neural crest cells marked by arrowheads. (I) Transverse section through the spinal cord, illustrating expression in the dorsomedial somite (som) closest to the neural tube, and in an intermediate zone of the CNS.