Fig. 5. Fgf signal and Spr2 mediate inductivity of Nodal signal on ntl. The embryos were examined for ntl expression. (A–D and I–K) 75% epiboly stage. (E–H and L–N) Bud stage. Almost all of the embryos injected with 0.5 pg sqt mRNA alone showed a large increase in ntl expression in the axial mesoderm (B and F). Co-injection with 100 pg XFD mRNA effectively inhibited the inductivity of sqt overexpression (C and G). Co-injection with 5 ng spr2-MO2 also inhibited, although less effectively, the inductive activity of sqt overexpression (D and H). Injection with 100 pg lefty1 mRNA almost abolished ntl expression during midgastrulation (J). Co-injection with 50 pg spr2 mRNA rescued ntl expression in some of the embryos (K). At the bud stage, the rescue effect of spr2 mRNA injection was also obvious (M and N).