Fig. 8 Spry4 antagonizes FGF signaling pathway in vivo. (A1) fgf8 (or fgf3) mRNA is injected with rhodamine dextran into one blastomere of the 16 cell stage embryo. (A2) If the progeny of the injected cells comes to lie in the ventral aspect of the early gastrula, a secondary embryonic axis is formed (A3). (B) At the 16-cell stage, two batches of embryos that have been previously saturated with lacZ- or spry4-mRNA are co-injected into one blastomere with eGFP- and fgf8 (or fgf3) mRNA. The GFP allows to identify ventrally located clones. Spry4 inhibits the effect of ventral Fgf8 misexpression (C) or ventral Fgf3 misexpression (D). (E) Injection of 60 pg CA-FGFR1 (CA-R1) strongly dorsalizes embryos (1) co-injection of 125 pg (2) or 250 pg spry4 mRNA (3) progressively rescues the dorsalized phenotype to wild type. (F) Localized injection of CA-FGFR1 in one blastomere at the 16-cell stage induces a strong activation of ERK at blastula stage. (G) Overexpression of spry4 inhibits activation of MAPK at gastrula stage.
