snakes vs anoles

In contrast to snakes, anoles (a type of lizard) possess more limb structures such as the tibia and fibula. The presence of more limb structures is partially due to different expression patterns of the Sonic Hedgehog gene. A team of researchers (led by Leal and Cohn) found that in anole leg buds, expression is more sustained and in pythons’ expression is transient. The ZRS domain in anoles was also found to bind more strongly to transcription factors than the python’s ZRS domain. The differences between enhancer elements for the Sonic Hedgehog gene indicate how the gene was able to evolve over time. Mutations that have lowered enhancer binding could have down-regulated the Sonic Hedgehog pathway, leading to limb reduction in snakes. In many vertebrates from anoles to humans, the amount of limb development shows a direct relationship with the activity of the Sonic Hedgehog enhancer.