Two studies pinpoint a stretch of DNA that could explain how snakes evolved from four-limbed animals.

A team led by Len Pennacchio and Axel Visel at Lawrence Berkeley National Laboratory in California analysed the ZRS DNA sequence — which regulates a key limb-development gene called Sonic hedgehog (SHH) in a range of animals — in the genomes of various snakes. The authors found that snakes' ZRS sequence differs markedly from that of other vertebrates. Mice in which the ZRS had been replaced by the cobra or python version did not express SHH in their developing limbs and were born with stumps instead of legs.

In a separate study, Francisca Leal and Martin Cohn at the University of Florida in Gainesville identified a series of deletions in the ZRS common to several snake species, but not seen in limbed vertebrates. In experiments in mice and cell culture, these mutations reduced the activity of the ZRS.

Cell 167, 633–642 (2016) ; Curr. Biol. http://doi.org/br4z (2016)