Fig. 7. Ras-dva downregulation, in contrast to Ras, can interrupt FGF8a signaling in the anterior ectoderm. (A) Two crescent-shaped stripes of the FGF8a expression in the anterior ectoderm of the Xenopus neurula (left half) are exactly coincident with the anterior and posterior borders of the Ras-dva expression domain (right half). (B-D) Ras-dva downregulation, in contrast to Ras, interferes with FGF-8a signaling in anterior ectoderm in Xenopus embryos. (B,B') FGF-8a mRNA injection induces ectopic BF-1 expression (red arrow). (C,C') Co-injection of FGF-8a and DN-Ras-dvaT22N RNAs results in inhibition of BF-1 expression in the injected area (black arrow). (D,D') Co-injection of DN-RasS17N with FGF8a did not affect the BF-1 activating signal from FGF8a (red arrow). These results were revealed by whole-mount in situ hybridization in neurula stage Xenopus embryos. All embryos are shown from the anterior, dorsal side upwards.