Involvement of the Sonic hedgehog gene in chick feather formation.

To elucidate the molecular mechanisms of chick feather formation, we observed expression patterns of the Sonic hedgehog (Shh) gene, which is one of the vertebrate homologs of the Drosophila segment polarity gene, hedgehog, and encodes a signaling molecule functioning in limb pattern formation and motor neuron induction. We found that the Shh gene is also expressed in the apical region of the feather placodes and then in nine to eleven longitudinal stripes along feather filaments. The stripe was found to correspond to one of the outer marginal zones of each barb ridge, termed the zone of Shh expression. No significant expression signal was detected in the scale bud of developing legs. Thus, Shh is likely to function as an epithelial signaling molecule in epithelio-mesenchymal interaction during feather formation. Furthermore, since genes of bone morphogenetic protein-2 (BMP-2) and fibroblast growth factor-4 (FGF-4) are coexpressed with Shh during feather formation as observed in limb morphogenesis, interactions among FGF-4, Shh and BMP-2 may be involved in formation of feather filaments and barbs in a similar fashion as elucidated in limb pattern formation.