An article published in the journal “Nature” describes a research on the evolution of from fins to hands. A team of scientists coordinated by paleontologist and developmental biologist Neil Shubin of the University of Chicago, Illinois, used the CRISPR-Cas9 genetic engineering technique to show that the same cells that generate fish fin rays have a central role in the formation of tetrapods fingers and toes.

Neil Shubin has been studying the transition from fins to feet for over two decades. In the course of his research, he discovered fossil species such as Tiktaalik, which was already showing the adaptation of rear fins, described by the team led by Shubin in a research published in January 2014. In addition to palaeontological research, Shubin has been pursuing other biological ones related to the exams of the development of embryos comparing those of fish and tetrapods.

Other researchers had already analyzed the DNA of different species such as mice to determine which genes were essential to the development of their legs. Two genes called Hoxha-13 and Hoxd-13 turned out to be crucial and when their function is suppressed leg bones develop normally but not those of the wrists and ankles nor they develop their fingers and toes.

Neil Shubin knew that fish have genes similar to Hoxha-13 and Hoxd-13 therefore decided to focus on them. In particular, in his experiments he used specimens of zebrafish. Tetsuya Nakamura, part of his team, used the CRISPR-Cas9 genetic technique to suppress the genes associated with the growth of the fins in these fish breeding specimens in which different genes were suppressed to verify the differences in their development.

The result was that none of the mutant fish developed complete fins. However, some developed fins with similarities to fingers made of the same type of bone that generates fingers in tetrapods. As a paleontologist, Neil Shubin thought that finger bones were of a kind different from those of fin rays but the result of these experiments suggested otherwise.

The genetic modification experiments of fish began in 2013 and included high-energy CT scans on adults specimens to examine the structure of their fins. Some parts may be invisible to normal exams, even using ordinary microscopes, so specific exams were needed to understand exactly how the fin structures developed with certain combinations of genes.

This research represents another step forward in the understanding of the evolution from fish to tetrapods. The discovery of new fossil species in which legs were developing would be useful but in the field of paleontology there’s always an element of luck. Instead, genetic studies will continue to better understand why certain cells form structures as different as fish fins and tetrapod limbs.