FGF2 activates ectopic Spry2 expression. (A, B) FGF2 beads implanted adjacent to flank level somites of HH16 embryos induced outgrowth of an ectopic limb bud with Spry2 expression near the tip (arrowheads), Spry2 expression is expanded at the base of the forelimb (in A, arrowhead) or hindlimb bud (in B) towards the bead. (C, D) FGF4 beads implanted adjacent to flank level somites of HH16 embryos do not induce ectopic Spry2 expression. (E, F) PBS control beads implanted similarly to that of FGF2 and FGF4 at the level of the forelimb (E) or hindlimb (F) flanks and show normal Spry2 expression. fl: Forelimb, hl: hindlimb. Magnifications: 18x in (A, B), 22x in (C, D, E), 24x in (F).