Fig. 4. Donor neural crest can also delay molecular and histogenic programs of cranial feather development. (A) Duck cranial neural crest cells follow their own timetable for differentiation when transplanted into quail hosts. Resultant duail chimeras collected at HH36 contain feather buds as well as epidermal regions that lack placodes (broken outline). The absence of epidermal placodes is equivalent to that observed on control embryos at HH33 (compare with Fig. 2G). (B,C) The presence and absence of cranial feather buds can be seen in sections stained histologically with trichrome (TC). (D) Immunohistochemical analyses using an anti-quail antibody confirm that wherever placodes are present, the dermis is derived from quail host neural crest (Q¢PN positive, black cells). (E) By contrast, regions that lack placodes contain dermis derived from the duck donor (Q¢PN negative). (F,G) Bmp4 is expressed in mesenchyme derived from the quail host but is not yet detected in mesenchyme of duck donor origin. (H,I) Shh is expressed in the epithelium overlying dermis from the quail host but not over dermis derived from the duck donor. (J,K) Delta1 is detected in quail host dermis but not in duck donor-derived dermis. (L) Duail chimeras collected at HH39 have normal long feather buds alongside areas containing short feather buds like those observed on HH36 controls. (M) Immunohistochemical analyses confirm that the short feather buds, which are like those of a HH36 duck instead of a HH39 quail, are derived from duck donor neural crest (Q¢PN-negative). (N) Long feather buds composed of quail host epidermis (Q¢PN-positive) and duck donor dermis (Q¢PN-negative; arrow) are present in duail chimeras at HH42. Scale bar: 1 mm in A; 100 µm in B-K; 1 mm in L; 50 µm in M; 100 µm in N.