Fig. 7. Fgf10 maintains Tbx5 expression during limb initiation. (A) Beads soaked in SU5402 were applied to the LPM of stage 15 chick embryos. At stage 17, Tbx5 expression was strongly reduced on the manipulated side (arrow). An asterisk indicates the position of the implanted bead. (B-D) fgf10 maintains tbx5 expression in the presumptive pectoral fin bud field of zebrafish. In the hst mutants, tbx5 expression is downregulated at 26 hpf. In addition, the few remaining tbx5-expressing cells fail to condense into circular areas of the forming fin buds. (C, compared to the wild-type embryo in panel B). The expression is no longer detected at 36 hpf (not shown). (D) fgf10 RNA was injected into hst mutant embryos at the one-cell stage, resulting in the maintenance of tbx5 expression in the pectoral fin bud region at 36 hpf, although the fin buds were not formed. Magnified view of the pectoral fin region, anterior to the left.