Fig. 8. (A) Transverse section of the limb bud processed for TUNEL showing the increased cell death 24 hours after the implantation of an FGF-bead into the anterior margin mesoderm. Note that apoptosis is induced at some distance form the bead (*). (B,C) Upregulation of Snail (B) and MSX2 (C) 16 and 24 hours, respectively, after implantation of an FGF-bead (*) into the anterior margin mesoderm of the chick wing bud. (D-H) Regulation of BMP gene expression between 5 and 20 hours after implantation of FGFs in the anterior (E-G) or posterior margins (D,F,H) of the bud at stages 20-22: BMP2 (D); BMP4 (E,F); and BMP7 (G,H). Note the expanded domains of bmps in the treated limbs in comparison with the contralateral control limb. (I) Scanning electron micrograph showing the flattening of the AER 24 hours after the implantation of an FGF-bead in the anterior margin of the wing bud. Arrows indicate the anterior end of the AER.