Fig. 3. Fgf function is epistatic to vhnf1 function in the posterior hindbrain. (A-D) 18-somite stage embryos, dorsal view, anterior to the left. (A,B) hoxb1a expression is normally limited to the presumptive r4 domain (A) but is expanded to the posterior in vhnf1 mutant embryos (12/47 embryos) (B). (C,D) Morpholino oligos (MOs) directed against both fgf3 and fgf8 injected into embryos derived from vhnf1 heterozygous parents. Most (37/40) embryos show hoxb1a expression limited to the r4 domain (C). Expression of hoxB4 (purple) and krox20 (orange); all (56/56) embryos show no anterior expansion of hoxB4 expression (D). (E-G) One-somite-stage embryos, dorsal view, anterior to the top. (E,F) Injection of MOs directed against fgf8+fgf3 does not affect vhnf1 expression (E), although is sufficient to inhibit r5 krox20 expression in sibling embryos (F). (G) Clutches of embryos produced by vhnf1 heterozyogous parents show consistent expression of fgf8 in all embryos.