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

The study explores the impact of transient activation of the sonic hedgehog (Shh) pathway on skin appendage fate in chicken embryos, demonstrating that a single injection of a Shh pathway agonist (SAG) at embryonic day 11 can permanently transform scales into feathers. This transformation was observed in 9 out of 20 embryos, with ectopic feathers developing similarly to normal feathers and persisting into adulthood. RNA sequencing confirmed the up-regulation of Shh pathway genes, indicating that this pathway plays a crucial role in the transformation. The findings suggest that variations in Shh signaling may contribute to the diversity of bird skin appendages.