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Fig. 6. FoxF1 is a target and a mediator of BMP4 signaling. (A) RT-PCR analysis of RNA isolated from animal caps injected with BMP4 RNA. Animal caps from embryos injected with BMP4 RNA (1.5 ng) into the animal blastomeres or uninjected embryos were dissected at stage 8 and collected when siblings reached stage 12.5. Xbra was used as a positive control for BMP4 induction and EF1{alpha} as a loading control. Lane 1 - RT-PCR on RNA from a whole embryo. Lane 2 - uninjected cap. Lane 3 - BMP4 injected cap. Lane 4 - no RT (no enzyme, RNA from the whole embryo). (B) RT-PCR analysis of RNA isolated from animal caps injected with BMP4 or Xbra RNA, or treated with FGF protein. Animal caps from embryos injected with BMP4 (1.5 ng) or Xbra (2.5 ng) RNA into the animal blastomeres or uninjected embryos were dissected at stage 8. Caps were collected when siblings reached stage 12.5 and assayed by RT-PCR. For FGF experiments, a set of uninjected caps was dissected at stage 8 and treated with 200 ng/ml bFGF for 1 hour. (C-F) Effects of FoxF1 RNA injection on the morphology of Xenopus embryos. Two dorsal blastomeres at the 4-cell stage were injected with FoxF1 RNA (0.4-1 ng), and phenotypes were analyzed at stage 28-30. The injected embryos (D) show different degrees of ventralization, while their siblings (C) display normal morphology. (E,F) The right (E) and left (F) side of a stage-30 embryo injected in the left side with FoxF1 RNA immunostained with 12/101 antibodies that recognize somatic mesoderm. The left side of the embryo shows a significant reduction of this marker. (G,H) FoxF1 RNA can rescue axis duplication caused by the injection of dominant-negative BMP receptor (DNBR). (G) Embryos injected with DNBR RNA (1.5 ng) showing axis duplications. (H) Embryos injected with DNBR and FoxF1 RNA (1.5 ng, 1.25 ng) demonstrate that FoxF1 RNA can rescue the DNBR phenotype.