b-catenin in Epithelial Morphogenesis: Conversion of Part of Avian Foot Scales into Feather Buds with a Mutated b-Catenin

We explored the role of b-catenin in chicken skin morphogenesis. Initially b-catenin mRNA was expressed at homogeneous evels in the epithelia over a skin appendage tract field which became transformed into a periodic pattern corresponding to ndividual primordia. The importance of periodic patterning was shown in scaleless mutants, in which b-catenin was initially expressed normally, but failed to make a punctuated pattern. To test b-catenin function, a truncated armadillo fragment was expressed in developing chicken skin from the RCAS retrovirus. This produced a variety of phenotypic changes during epithelial appendage morphogenesis. In apteric and scale-producing regions, new feather buds with normal-appearing follicle sheaths, dermal papillae, and barb ridges were induced. In feather tracts, short, wide, and curled feather buds with abnormal morphology and random orientation formed. Epidermal invaginations and placode-like structures formed in the scale epidermis. PCNA staining and the distribution of molecular markers (SHH, NCAM, Tenascin-C) were characteristic of feather buds. These results suggest that the b-catenin pathway is involved in modulating epithelial morphogenesis and that increased b-catenin pathway activity can increase the activity of skin appendage henotypes. Analogies between regulated and deregulated new growths are discussed. © 2000 Academic Press