By modifying a specific gene, scientists have discovered a way to permanently transform the scales on a chicken’s legs into feathers. The results provide new insight into the evolutionary origins of the bird from the dinosaurs.
“Like birds, it is clear today that many dinosaurs were partially covered in feathers as well as scales,” said Michel Milinkovitch, professor in the Department of Genetics and Evolution at the University of Geneva and co-author of the new research. “In birds, it’s similar. So by changing this gene, we can actually increase or decrease the proportion of the body that is covered in feathers or scales depending on when exactly this gene is expressed.”
To perform this genetic switcheroo, Swiss scientists targeted the sonic hedgehog (Shh) gene, which controls a signaling pathway that determines the development of certain characteristics at the embryonic level. This includes the brain and spinal cord; members; and appendages, such as scales and feathers, according to the study published May 17 in the journal Science Advances. (And, yes, Shh is named after the titular character in the popular video game.)
In the lab, the scientists used a process known as “egg candling,” which involves using a light source to illuminate blood vessels inside an egg. This allowed them to identify a suitable vessel to directly inject a molecule that activates the Shh pathway into the developing embryo. For the study, they used broiler chickens (Gallus gallus domesticus), which are raised for commercial meat production, according to a statement.
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“We performed the injection on day 11, which is the exact time when the scales normally appear on the embryo,” lead author Rory Cooper, a postdoctoral researcher in artificial and natural evolution at the University, told Live Science. from Geneva. “If we perform the injection even a day too late, the embryo has already started to develop scales.”
After hatching from the eggs, scientists noticed the formation of fluffy juvenile feathers on the legs of the chicks. These super soft feathers were comparable to the feathers covering the rest of their bodies, according to the statement.
“The effect is really clear once they hatch,” Cooper said. “And the change lasts. Once the chickens grow their feathers, they don’t find scales on the targeted area.”
The researchers were surprised at how easily it was possible to change the shape of chickens’ legs and said it gave the team a new understanding of the evolution of these animals.
“Feathers are a function of change,” Milinkovitch told Live Science. “In dinosaurs, feathers could have been used to regulate the animal’s internal temperature or as a colorful display. Flight came later. By altering the expression of a gene, we were able to create a cascade of developmental effects that triggered feather growth, offering new insight into the evolution of these animals.”
