Fig. 4. Spry2 is a feedback inhibitor of Fgf signalling. (A) Wild-type expression of spry2. (B) Inhibition of Fgf signalling by injection of RNA encoding dn-fgfr abolishes spry2 expression. (C) Ubiquitous or (D) localised (arrowhead) overexpression of fgf8 RNA induces ectopic spry2 expression. (F) spry2 expression is reduced in fgf8/ace mutant embryos compared with wild-type siblings (E). Compared with wild-type (G) embryos injected with fgf8 RNA (H) display dorsalised phenotypes. (I) Co-injection of fgf8 with spry2 RNA rescues embryos. (J,O,L) Injection of (J) mo-spry2 or (O) dn-spry2, or (L) co-injection of both induce dorsalised phenotypes. Compare with injection of fgf8 RNA (H,P). (K) Dorsalisation is abolished by co-injection of mut-spry2. (A-D) Late blastula stage, (E-P) early segmentation stage. (A-C) Animal pole views; (D-L) lateral views; (M-P) dorsal views. (E,F,M-P) Anterior is towards the left.