FIBROBLAST GROWTH-FACTOR-2 CAN REPLACE ECTODERMAL SIGNALING FOR FEATHER DEVELOPMENT

The initiation and morphogenesis of cutaneous appendages depend on a s eries of reciprocal signaling events between the epithelium and mesenc hyme of the embryonic skin. In the development of feather germs, early dermal signals induce the formation of epidermal placodes that in tur n signal the mesoderm to form dermal condensations immediately beneath them. We find a spatially and temporally restricted pattern of transc ription for the: genes that encode fibroblast growth factor (FGF) 2 an d FGF receptor (FGFR) 1 in developing feather germs of the chicken emb ryo. PGF-2 expression is restricted to the epidermal placodes, whereas FGFR-1 expression is limited to the dermal condensations. Transcripti on of these genes could not be detected in skins of scaleless (sc/sc) embryos that fail to develop feathers as a result of an ectodermal def ect, Treatment of sc/sc skins with FGF-2 results in the formation of f eathers at the site of application of the growth factor and the induce d feathers express FGFR-1 in their dermal condensations. Thus, we have established FGF-2 as an epidermal signal in early feather germ format ion. The observation that FGF-2 can rescue the mutant phenotype of sc/ sc embryos suggests that PGF-2 either is, or is downstream from, the s ignal that the sc/sc mutant ectoderm fails to generate.