Restriction of Wnt1 expression to the ventral side during gastrulation requires Nodal. (A-C) At blastula stages (16 hour and 24 hour), wnt1 mRNA is detected in a ring near the posterior end of the embryo. (D,E) At gastrula stages (34 hour and 44 hour), wnt1 mRNA expression is strongly enriched in ventral cells near the posterior end. (F) In a Nodal morphant, wnt1 mRNA accumulation is radialized at the posterior end at gastrula stage (compare D and F). LV, lateral view; PV, posterior view. Scale bar: 20 μm.