Transient Agonism of the Sonic Hedgehog Pathway Triggers a Permanent Transition of Skin Appendage Fate in the Chicken Embryo

The study demonstrates that transient activation of the sonic hedgehog (Shh) pathway in chicken embryos can permanently change the fate of skin appendages from reticulate scales to feathers on the ventral surfaces of the foot and digits. The ectopic feathers are similar to normal body feathers, evolving from down-type to regenerative contour feathers in adults. This transformation does not require ongoing treatment, and RNA sequencing shows that the treatment enhances the expression of Shh pathway-related genes. The findings suggest that variations in Shh signaling may play a role in the diversity of avian skin appendages.