Fig. 1

Canonical Wnt Signaling Promotes Mesodermal and Inhibits Neural Development during Postgastrulation Development (A–D) The HS:dkk1 transgenic line was used to inhibit canonical Wnt signaling during postgastrula stages. (A and B) myod expression in wild-type and transgenic embryos that were heat-shocked at bud stage and fixed at 24 hpf. In transgenic embryos, there is a severe truncation of the mesodermally derived somites (B, arrow), despite the overall length of the embryo being similar to wild-type embryos. (C and D) sox3 expression in wild-type and transgenic embryos. An enlarged neural tube is present in the posterior embryo, beginning where somites are absent (D, arrow). (E–G) Cells within the stem zone (SZ; G, arrowhead) express both the mesodermal progenitor marker ntl and the neural progenitor marker sox2. (H–J) The cell population expressing both ntl and sox2 is different than cells that have committed to the mesodermal lineage, as marked by tbx16 expression (J, arrowhead showing nonoverlapping expression of ntl in the SZ). (K–N) Wild-type and HS:dkk1 transgenic embryos were heat-shocked at the 12-somite stage and fixed at the 16-somite stage (3 hr after the heat shock). (K and L) The expression of the mesodermal progenitor marker ntl is completely lost in the SZ of transgenic embryos, (M and N) whereas the expression of the neural progenitor marker sox2 is significantly expanded. The ntl notochord domain is unaffected by Wnt inhibition. Note the unique ventral sox2 domain (arrowheads). See also Figure S1.