![]() In addition to studying the Sonic hedgehog gene, the researchers also studied the enhancers of the Hoxd genes, which dictate the formation of fingers and toes. ![]() "In advanced snakes, which are completely legless (no rudiments at all), we found much more extensive mutations/degradation of the ZRS than we saw in either python or boa," he said. So while pythons have three deletions in the the limb-specific enhancer of the hedgehog gene (known as the ZRS), nearly identical ZRS degradation was also present in the boa constrictor, Cohn told Motherboard. "They make embryonic legs but the cells don't complete the process of skeletal development." "The results tell us that python limb development progresses much further than we knew before," Cohn said in a press release. During normal limb formation, the enhancer, or part of the DNA responsible for gene expression, acts as a genetic "switch" that goes on, but the mutations eradicated that switch.īy comparing the DNA of snakes and lizards, Cohn and Leal found that while some snakes, such as cobras or vipers, are totally without a hint of previous limbs, pythons and boa constrictors have tiny limb rudiments left over. ![]() Together, the mutations got rid of the region of the gene known as the transcription factor binding sites, where proteins and DNA bind together. The Sonic hedgehog gene is a key gene that signals limb development, and according to the new study, a trio of mutations that appeared roughly 100 million made the gene much less likely to be expressed. "What these results suggest is that the legs were not completely lost, in that the even python embryos start to form the skeletal elements of the entire leg, but the distal parts degenerate." "These transient embryonic legs give us a window in the evolutionary history of snakes by showing us that they have retained a remarkable amount of machinery needed to make limbs," Cohn said.
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