Why did snakes lose their legs
Biologists have tested the gene for leglessness of snakes
Researchers from the Lawrence Berkeley National Laboratory and Stanford University have proven the role of the gene enhancer in the fact that snakes have no legs. They did it using CRISPR-Cas9 technology.
An enhancer is a sequence in DNA that does not encode proteins, but regulates the activity of genes. A transcription factor protein is attached to the enhancer, and after that, the gene that is regulated by the enhancer begins to work.
The gene, which in snakes and other animals is responsible for the growth of limbs, scientists have named Shh (short for Sonic hedgehog) – in honor of Sonic the hedgehog, a character in a series of video games. As it turned out, the enhancer that regulates its operation is damaged in snakes: several sections are missing in it. Mutations make it difficult for the transcription factor to work, because of this, the enhancer does not work properly, and the legs of pythons and boas do not grow properly, remaining at the rudimentary stage.
Scientists used a scientific tool that allows you to edit the genome with high accuracy – CRISPR-Cas9. With his help, they built into the mouse genes an incorrect, snake enhancer with mutations that disrupt its work. As a result, the mice never formed normal legs. Mice that were transplanted with enhancers of the same gene from fish and humans grew normal limbs.
At the top – a mouse with a normal Shh enhancer, at the bottom – with a snake. Photo from an article in Cell.
As the researchers write, their work convincingly proves that the snakes lost their legs due to malfunctions in the Shh gene enhancer. In addition, they say that their work is another confirmation of the effectiveness of the CRISPR–Cas9 method for genome editing.
The study is published in the journal Cell (Kvon et al., Progressive Loss of Function in a Limb Enhancer during Snake Evolution).
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25.10.2016