The Miracle in feathers
American geneticists have turned crocodile scales into feathers
Scientists from the USA have created a kind of analogue of the "duckworm", a mythical crocodile with feathers, changing the work of some of the key genes responsible for the formation of scales in these lizards, according to an article published in the journal Molecular Biology and Evolution (Wu et al., Multiple regulatory modules are required for scale-to-feather conversion).
"Now we have a potential "lost link" in the evolution of dinosaurs and birds, a molecular genetic explanation of how their ancestors lost scales and acquired feathers. Our observations show that strong and weak changes in the activity level of genes controlling the growth of scales have completely different effects on changes in their shape and appearance, which suggests that the scales could really be the "ancestors" of feathers," said Cheng-Ming Choung from University of Southern California in Los Angeles (USA).
In recent years, many well-known paleontologists, such as Jack Horner and a number of geneticists are actively working on the creation of a "chicken dinosaur", trying to turn ordinary modern birds into a kind of dinosaur. Despite the seemingly fantastic nature of this task, biologists have achieved tremendous success in this field in the last five years.
For example, recently they managed to turn the beak of a chicken embryo into a structure similar to the toothy jaw of a dinosaur, return the legs of a typical lizard of the Mesozoic era to the "hen", as well as "resurrect" many other features of ancient lizards. It remains to solve only a few major tasks – to return the future "reptile" tail and make it grow scales instead of feathers.
Chun and his colleagues took the first step towards solving this problem by discovering a set of genes that control the growth of scales in crocodiles, and modifying them in such a way that they began to turn into a kind of feathers.
As the geneticist explains, scientists have long believed that the feathers of ancient reptiles arose as a result of mutations in the genes responsible for the formation of scales, but they had no evidence of this, due to the absence of fossilized remains of "lost links" of evolution. Some paleontologists even believed that the feathers could have arisen as a result of changes in the work of some other skin structures, which later completely replaced the scales.
Scientists tried to test these theories by studying which genes were most active in future skin cells in the embryos of chickens and alligators, and identifying several interesting sites in the DNA of birds that work quite differently from their ancient relatives. Having discovered these genes, Chun and his colleagues thought about what would happen if they were changed in a similar way in the crocodile genome.
By including each of these genes in the DNA of the embryos, the scientists observed changes in the shape of the future scales of the lizards, noting those parts of the genome that made it more like feathers. As a result, biologists were able to find five genes – Sox2, Zic1, Grem1, Spry2 and Sox18 – mutations in which made the scales of alligators look like either the down and primitive feather cover of ancient dinosaurs, or the feathers of modern birds.
Each of these genes, as scientists note, plays its own role in this process. For example, Sox2 suppresses the formation of scales and is responsible for the work of feather bulbs, and Grem-1 causes feathers to branch and acquire beards. Other sites, such as Sox18, control the development of the general appearance of the feather and they arose, according to geneticists, at the last stages of the evolution of the common ancestors of feathered dinosaurs and birds.
The study of these genes, as Chun hopes, will help his team to solve two problems – to understand how and why feathers appeared in dinosaurs, and to create a kind of "feathered dragon" from ancient Chinese legends, an eastern version of Horner's "chicken" or "duck-tail" creationists.
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