Fig. 3

A Single Cell Transplantation Assay Demonstrates that Wnt Signaling Specifies Mesodermal Fate in Bipotential Neural/Mesodermal Stem Cells throughout Body Formation (A and B) Host embryos were visualized under a fluorescent microscope immediately after the single cell transplant to verify that only one cell was transplanted (A, arrow). An overlay with the bright field image illustrates the position of the single cell in the ventral margin of the host embryo (B, arrow, animal pole of the embryo is to the top). (C and D) Single cell transplantations into the ventral margin produce lineage restricted clones, primarily giving rise to clones within the somites (C) with some contributing only to the neural tube (D). (E and F) Single HS:TCFΔC cells transplanted into wild-type host embryos and heat-shocked at bud stage produce morphologically normal muscle fibers (E) and spinal cord neurons (F). (G) Quantification of one-cell transplants of control or HS:TCFΔC indicate that Wnt signaling is required continuously throughout development to specify mesoderm in a bipotential neural/mesodermal stem cell. Inhibiting Wnt signaling before or after gastrulation causes a significant decrease in clones that contribute to the somites and a significant increase in the clones that give rise to spinal cord neurons (p < 0.05 indicated by red asterisk). Nonmuscle mesoderm (see Figure 4) is not included in these graphs so the totals do not add up to 100%. See also Figure S4.