Scientists transform scales on chicken feet into feathers by simply tweaking a gene

In addition, the scientists used the 'egg candling' technique in the lab. “We used the classic technique of ‘egg candling’, in which a powerful torch illuminates blood vessels on the inside of the eggshell. This allowed us to precisely treat chicken embryos with a molecule that specifically activates the Shh pathway, injected directly into the bloodstream,’’ explained Rory Cooper, a post-doctoral researcher in Michel Milinkovitch’s laboratory and co-author of the study, in a statement. 

The research was carried out on broiler chickens (Gallus gallus domesticus), which are raised for commercial meat production. 

After this gene was altered, the embryonic chickens were programmed to grow feathers instead of scales on their feet, according to the authors. After the eggs hatched, the team noticed the chicken's feet were covered in supersoft feathers.

The research sheds new light on the evolutionary mechanisms of these animals. ‘‘Our results indicate that an evolutionary leap - from scales to feathers - does not require large changes in genome composition or expression. Instead, a transient change in expression of one gene, Shh, can produce a cascade of developmental events leading to the formation of feathers instead of scales,’’ said Milinkovitch. 

The results have been published in the journal Science Advances.

Study Abstract:

Vertebrate skin appendage early development is mediated by conserved molecular signaling composing a dynamical reaction-diffusion–like system. Variations to such systems contribute to the remarkable diversity of skin appendage forms within and among species. Here, we demonstrate that stage-specific transient agonism of sonic hedgehog (Shh) pathway signaling in chicken triggers a complete and permanent transition from reticulate scales to feathers on the ventral surfaces of the foot and digits. Resulting ectopic feathers are developmentally comparable to feathers adorning the body, with down-type feathers transitioning into regenerative, bilaterally symmetric contour feathers in adult chickens. Crucially, this spectacular transition of skin appendage fate (from nodular reticulate scales to bona fide adult feathers) does not require sustained treatment. Our RNA sequencing analyses confirm that smoothened agonist treatment specifically promotes the expression of key Shh pathway–associated genes. These results indicate that variations in Shh pathway signaling likely contribute to the natural diversity and regionalization of avian integumentary appendages.