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Feather
induction begins along the dorsal midline in the
lumbo-sacral region of the developing embryo with the
formation of thickened epithelial placodes. The epithelium
elongates, forming one short bud per placode. Feather bud
development involves the interaction and interplay of
epithelial and mesenchymal tissues which communicate using
soluble signaling molecules including Sonic Hedgehog (SHH).
Following dermal condensation, SHH is expressed in the
epithelium of the developing feather bud, and its receptor,
Patched, is expressed in the mesenchyme. Ectopic expression
of SHH using a retroviral vector can induce the development
of feather buds at abnormal locations (Morgan 1998).
SHH
expression is maintained during bud elongation, suggesting
that it continues to play an important role. The importance
of SHH signaling can be investigated using cyclopamine, a
teratogenic steroidal alkaloid found in the plant
Veratrum californicum. Cyclopamine has been shown to
effectively block SHH signaling (Cooper 1998; Incardona
1998). We treated dorsal skin explants of both Stage 28 and
Stage 31 chicken embryos (Hamburger & Hamilton 1951)
with cyclopamine to block SHH signaling during the
elongation of the feather
buds.
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