An article published in the journal “Nature” describes a research on the genome of the axolotl (Ambystoma mexicanum), a species of salamander that can regenerate its limbs but also a severed spinal cord and retinal tissue. A team of researchers sequenced this animal’s DNA to try to discover the secrets of its regeneration. This is the largest genome sequenced so far with its 32 billion bases.
A few weeks ago, the DNA sequencing of another species of salamander, the Iberian ribbed newt (Pleurodeles waltl), was announced. This species has a genome about six times larger than the human genome, the axolotl has a genome that is a little over 1.5 times larger that of Iberian ribbed newt and about ten times larger than the human one. Sequencing such a large DNA was a remarkable achievement for the team of researchers led by Elly Tanaka of the Research Institute of Molecular Pathology (IMP) in Vienna.
The sequencing was conducted through a series of readings of the axolotl’s DNA fragments for a total of 72,435,954 readings. To assemble the data of all those readings, the researchers who coordinated this phase, Gene Myers of the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) and Siegfried Schloissnig of the Heidelberg Institute for Theoretical Studies (HITS), needed to write a new software called MARVEL, available under a Creative Commons license on the GitHub website.
The second phase of the research was that of the analysis of the axolotl’s DNA, where the scientists started understanding which genes are involved in the regeneration. That genome is so large also because there are repeated parts but analyzing it some very interesting genes have been found. For example, many genes exist only in the axolotl and other amphibian species and are expressed in the regeneration of limb tissues.
A surprising discovery is that the axolotl’s DNA completely lacks a key gene in the development of muscles and some nervous tissues called PAX3. In its place another gene was found, called PAX7. The researchers tried to experiment with the gene by using one of the CRISPR techniques that are widely used today but also with a TALEN technique to see the results, generally negative for its regeneration functions.
Sergej Nowoshilow of IMP, one of the article’s authors, defined this DNA sequencing a turning point for scientists working with the axolotl, a milestone in a research that began over 150 years ago. The scientist pointed out that he and his colleagues now have a map in their hands to investigate how complex structures can re-grow.
Reproducing that kind of process in humans is still a far-away goal but the possibility of studying the DNA of the axolotl is crucial. But there’s a serious problem: the axolotl is an almost extinct species due to the destruction of its natural environment. It’s one of the cases in which human beings risk harming themselves with their behavior.