(A) hairy2 expression over time upon AER ablation and ZPA removal. AER ablation results in short-term down-regulation of hairy2 (Ai–iv), while ZPA removal impacts hairy2 only in a long-term fashion (Av–viii). Mild effects are observed at earlier time points (arrows). (B) AER/FGF signaling acts at short-range on hairy2. Upon partial ablation of either the posterior-AER (Bi–viii) or the anterior-AER (Bix–xvi), hairy2 is down-regulated only in the tissue immediately adjacent to the ablation site (arrows). Partial ablations were confirmed by fgf8 staining (Bi,ii,ix,x) and shh expression was assessed (Biii,iv,xi,xii). Dorsal view; anterior to the top.