Gene sequencing revealed that the snake had mutations that lost limbs and created strange body features.
Snakes are eccentric among vertebrates. Their bodies are too thin to accommodate more than one lung, they can smell with their tongues, and most strangely, they have no legs.
This harmless slug-eating snake (Pareas berdmorei) is one of 14 species of snakes that have been genome-sequenced in a project by Chinese scientists.
Now, a major research project that sequenced the genomes of many snakes has discovered mutations that likely caused snakes’ legs to disappear. Specifically, in this project, Jia-Tang Li, an herpetologist at the Chengdu Institute of Biology of the Chinese Academy of Sciences, and colleagues sequenced the genomes of 14 snake species belonging to 12 families, covers 150 million years of snake evolution. They also analyzed the genomes of 11 previously sequenced snake species.
Li said the most interesting finding was that three different parts of the PTCH1 gene, which controls limb growth in snakes, were missing DNA. Since all snakes have this mutation, this could be one of the important genetic bases for limb loss in snakes. When Li’s team introduced the same mutations to the PTCH1 gene in mice, the mice had much shorter toe bones than normal. This is further evidence that PTCH1 plays an important role in legless snakes, the team writes in the Cell journal paper.
The study also sheds light on other genetic traits of snakes. Previous studies suggested that the reptile had lost genes important for vision. But new research shows that the genes are still, just inactivated, and may have even been inactivated very early in snake evolution, from primitive underground snakes.
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The gene inactivation also seems to hold true for genes involved in high-frequency hearing, which results in shape-corrected reptile ear bones becoming more sensitive to vibrations.
And to make all the internal organs fit into the slim body, the snake also lost two genes, DNAH11 and FOXJ1, which are responsible for guiding embryonic development to ensure the animal’s body becomes symmetrical. – such as having 2 lungs.
This work is a step towards identifying genes that are important in the development of snakes and other vertebrates, including humans, thereby identifying genetic breakdowns that can cause illness or deformity, Li said.
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