Fig. 3.

Scale-feather metaplasia. (A,B′) Chick skin morphogenesis at 18 days and Shh expression at 12 days in control (A,A′) and retinoic acid-treated (B,B′) embryos. After retinoic acid treatment, overlapping scutate scales in the control are replaced upon by feathered scuta at 10 and 11 days. The expression of Shh, which is at a low level at the distal tip of the scuta, is up-regulated in two or three spots (arrowheads) of the scuta distal tip. After Prin & Dhouailly, 2004. Reproduced with permission of Int J Dev Biol. (C,D) The over-expression of beta-catenin results not only in the formation of supernumerary small buds in the feather fields (C), but also in scale-feather metaplasia (D). (C) After Noramly et al. 1999. Reproduced with permission of the Company of Biologists. (D) After Widelitz et al. 2000. Reproduced with permission of the Company of Biologists. f, feather; s, scuta. Bars: A,B: 1mm A′,B′,D: 200 µm, C: 250 µm.