Fig. 1. Quail-duck chimeric system to study cranial feather morphogenesis. (A) Cranial feather buds arise via interactions between the neural crest-derived dermis and the overlying epidermis. At HH33, there is little histological evidence for cranial feather development, but by HH34, epithelial placodes form in the epidermis and the mesenchyme aggregates into dense dermis. By HH36, the feather buds contain a discrete dermal condensation and they begin to rise above the level of the integument. Long buds are present after HH37. (B) Japanese quail and (C) white Pekin duck display considerable differences in the pattern, pigmentation and morphology of their head feathers. (D) Owing to their distinct maturation rates, quail and duck embryos that are stage-matched for surgery subsequently deviate in stage, which provides a potent experimental system with which to identify molecular signals that regulate feather morphogenesis. (E) Neural crest cells were cut either bilaterally (as shown) or unilaterally from the rostral neural tube and exchanged between quail and duck embryos stage-matched at HH9.5. Among other derivatives, these cells are destined to form much of the craniofacial dermis. (F) Chimeric `quck' feather follicles contain duck host epidermis and quail-derived donor dermis stained black with an anti-quail antibody (Q¢PN). Individual quail-derived melanocytes associated with the duck host epidermis are present. Scale bar: 1 cm in B,C; 100 µm in F.