Fig. 5. Rescue of chelerythrine chloride-treated limb buds by RA, a ZPA or SHH (A) Ectopic Shh expression in chelerythrine chloride treated wing buds. A yellow arrow indicates normal posterior Shh expression in the left wing bud. A red arrow indicates ectopic Shh expression induced by a now buried RA bead implant indicated by a green asterisk. (B) An example of the typical skeletal pattern of 10-day-old RA-rescued wing. A complete hand plate is produced, but reversed in polarity, owing to the placement of the RA bead at the anterior side of the wing bud. (C) Placement of chelerythrine chloride beads (cc) and a SHH bead in the wing bud. (D) Skeletal pattern of 10-day-old ZPA-rescued wing. Polarity is reversed due to placement of ZPA at anterior of wing bud. (E,F) Skeletal patterns of 10-day-old SHH-rescued wings. In E, polarity is reversed, owing to placement of SHH bead at anterior side of the wing bud. 2, digit 2; 3, digit 3; 4, digit 4; d, digit; f, forearm element; h, humerus; r, radius; s, scapula; u, ulna.