Fig. 7. Sp8 and Sp9 regulate Fgf8 expression and limb outgrowth. Frontal views (A-C,E,F) and a dorsal view (D) of Fgf8 expression in chick limb buds with the anterior towards the top. (G,H) Dorsal views of chick forelimbs with the anterior towards the top. (I-L) Dorsal views of chick forelimb skeletons. (M-R) Dorsal views of zebrafish embryos with the anterior towards the left. (A-F) Injection of virus was made on the right side; the left side serves as the contralateral control. Injection of RCAS-Sp8 (A) and RCAS-Sp9 (B) resulted in an expansion (arrowheads) of the Fgf8 expression domain in the developing limb. Injection of RCAS-VP16-N-Sp8 (C) and RCAS-VP16-N-Sp9 (D) resulted in the elongation of the AER marked by the elongated expression domain (arrowheads) of Fgf8. Injection of RCAS-EnR-N-Sp8 (E) and RCAS-EnR-N-Sp9 (F) resulted in downregulation of Fgf8 expression (arrowheads) in the limb. (G,H) Injection of RCAS-EnR-N-Sp8 caused an indentation (H, arrowhead), whereas control injection had no effect (G). (I,J) Injection of RCAS-VP16-N-Sp8 caused ectopic digit formation in the anterior domain (J, blue arrowheads) when compared with the control (I). (K,L) Injection of RCAS-EnR-N-Sp8 and RCAS-EnR-N-Sp9 caused hypoplasia of the limb, such as the formation of a small spike with unidentifiable elements (K, red arrowhead) and loss of cartilage elements (L, red arrowheads). (M-O) fgf8 expression at 36 hpf injected with a control morpholino (M), sp8 morpholino (N) and sp9 morpholino (O). sp8 and sp9 morpholinos downregulated fgf8 expression in the fin buds (red arrowheads). The embryos represent the typical `faint signal' phenotype. (P-R) prx1 expression in zebrafish injected with a control morpholino (P), sp8 morpholino (Q) and sp9 morpholino (R) at 36 hpf. sp8 morpholino and sp9 morpholino perturbed fin outgrowth, as visualized by prx1 expression in the fin mesenchyme (red arrowheads).