Discussion

The introduction of cyclopamine at the 20-hour stage induces massive cell death (due to Shh inhibition) in both the tail bud region and the craniofacial region. This can be seen through regions of brightly stained dead cells. Fig 1. Deformations in later stages in the tail bud (Fig.2) are caused by the apoptosis of developing cells. After five days of exposure to cyclopamine the tail bud region is smaller and damaged at the posterior end.

Conclusion
- Thus Shh was found to be a necessary survival factor in avian tail bud development among its many other functions.