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Results

Treatment of cultured skin explants from either stage 28 or stage 31 embryos with cyclopamine resulted in the arrest of feather bud development. In contrast, control explants treated with HPCD continued to develop, reaching the short bud stage. Stage 28 explants treated with cyclopamine exhibited only faint signs of developed placodes (Figure 1). Thickened placodes were apparent in stage 31 explants treated with cyclopamine (Figure 2), but these placodes were present prior to culture. The presence of cyclopamine during culture prevented any further feather bud development. Therefore, SHH signaling appears to be essential for feather bud outgrowth. In addition, following treatment with cyclopamine no shh expression was detected in the epithelium above the placodes (Figure 3). Cyclopamine has been previously shown to act on the cells responding SHH and not to directly interfere with its expression (Cooper 1998; Incardona 1998). This suggests that SHH signaling is required to maintain shhexpression, possibly as part of a feedback loop (Figure 4).