Fig. 4. Spr2 mediates Fgf signaling in mesoderm induction. The embryos were examined for ntl expression. (A–E) 75% epiboly stage. (F–J) Bud stage. Injection with 10 pg fgf17b mRNA caused expansion of ntl expression in the axial mesoderm of most of the embryos (B and G), whereas the proportion of the embryos with similarly enhanced ntl expression significantly dropped when co-injected with the same amount of fgf17b mRNA and 5 ng spr2-MO2 (C and H). Injection with 50 pg XFD mRNA led to slightly smaller axial mesoderm domain and interrupted germ ring domain (indicated by arrows) for ntl expression (D and I), while the inhibitory effect of XFD was deterred when co-injected with 200 pg spr2 mRNA (E and J).