As part of their study of feather evolution, scientists have tried to restore the original appearance of chickens. They succeeded, but only temporarily.
By inhibiting the key gene Sonic Hedgehog at the stage of embryonic development, scientists have managed to make chicken feathers more similar to the tubular proto-feathers that probably first appeared in the ancestors of dinosaurs in the early Triassic period 250 million years ago. The newly hatched chicks had slowed feather development and some bare areas. However, within a few weeks, their feathers became the same as those of all other birds of their species.
The research was conducted to find out when, how and why the feathers first appeared. Prior to that, the researchers had also made changes to the Sonic Hedgehog gene in an attempt to produce chickens with feathers on their legs.
«Our experiments demonstrate that while a short-term disruption of the development of scaly foot skin can permanently transform it into a feathered foot, it is much more difficult to permanently disrupt the development of the plumage. It is obvious that in the course of evolution, the network of interacting genes has become extremely robust, ensuring the correct development of feathers even under significant genetic or environmental influences», — recognizes the lead author of the study, Professor genetics andevolutions at the University of Geneva Michel Milinkovic.
The fact that the researchers failed to produce chickens with full plumage like dinosaurs does not mean that the study was a failure. Milinkovic and co-author Rory Cooper, a researcher at the University of Sheffield, demonstrated how much the Sonic Hedgehog gene influenced the evolution of feathers. The first feathers were not the same as those seen in modern birds. They were tiny single tubular growths. In the process of evolution, they turned into all the different types of feathers of modern birds, from soft down to bright feathers peacocks.
Milinkovic and Cooper pioneered a technique called fluorescence light sheet microscopy to study the development of chicken feathers during the embryonic stage. This technique uses lasers to display thin fragments of a sample.
At the embryonic stage, feathers begin to develop into future chicks 9 days after the hen lays an egg. Spots called placodes appear all over the embryo of the future chicken. These placodes become kidney-like spots that later develop into all forms of feathers we know, using keratin, the same protein found in human hair and nails. The Sonic Hedgehog gene plays an important role in the embryonic development of chickens.
On the ninth day of the chicken embryo’s development, the researchers injected an inhibitor of the Sonic Hedgehog gene and watched what happened next. Within a few days, feather growth slowed down. The inhibitor inhibited the development of a complex, branched pattern. However, by day 17, feather growth had partially resumed, as the effect of inhibiting the Sonic Hedgehog gene was no longer in effect.
The hatched chicks had heterogeneous feathers, sometimes with bare skin. They also lacked outer plumage with a characteristic structure called a rachis
it is the axis of a bird's feather, consisting of a hard, tubular part called the calamus and a more flexible part called the shaft. On the 49th day of life, these chickens molted, and the new feathers that appeared developed normally.
The results of the research showed that the Sonic Hedgehog gene is involved in the evolution of protofeathers into modern feathers, as well as in the formation of feathers of different shapes and sizes in different species.
«The big challenge now is to understand how these genetic interactions changed to enable the emergence of proto-feathers in the early stages of dinosaur evolution», — explains Michel Milinkovic
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