Fig. 4

NaClO₃ Treatment Phenocopies extl3/ext2 Mutants, Causing Loss of Fgf Signaling and Resulting in Expansion of the Wnt Domain

(A and B) In NaClO₃-treated embryos, the prim stalls.

(C-D′′) NaClO₃-treated embryos show downregulation of HS levels by 10E4 antibody staining.

(E-F′′) extl3/ext2 mutants show a similar loss of HS.

(G-H′) NaClO₃-treated Wnt reporter line embryos show expansion of the Wnt domain in the prim, as evidenced by destabilized GFP (dGFP) expression and dgfp in situ hybridization.

(I-J′) The Fgf target pea3 is restored in NaClO₃-treated prim after CAfgfr1 induction.

(K-L′) Restored Fgf signaling restricts expression of the Wnt target lef1 back to the leading region.

(M-N′) The restored restriction correlates with the activation of dkk1b after Fgf pathway activation.

(O-T′) Wnt is restricted after NaClO₃ treatment by inducing Dkk1b expression in the Tg(hsp70:dkk1b-GFP) line. In the absence of HS, Dkk1b induction is sufficient to restrict the Wnt targets lef1 and fgf3 back to the leading region (O-P′ and Q-R′), but not to restore Fgf signaling in the trailing region of the prim (S-T′). pea3 is still only expressed in cells surrounding the prim (T′).

See also Figure S4, Table S1, and Movies S5 and S7.