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The axolotl is an astonishing creature, and scientists now have a better opportunity to understand its special features following the assemblage of the amphibian’s genome. The sequencing of a new species' genome has become common, but the axolotl stands out because it has 10 times as many nucleobase pairs as humans. It is hoped the work will eventually teach us how to apply its astonishing powers of regeneration to humans.
Axolotls have been bred for research since 1863. This has turned out to be fortunate, as their native habitats have been drained, or are threatened by the expansion of Mexico City. A year ago the axolotl genome was sequenced for the first time, but for Dr Jeramiah Smith this was just the start.
The original sequencing didn’t reveal how different parts of the genome fitted together, instead consisting of thousands of stretches of DNA. Individual genes could be resolved, but the way they interact with their neighbors was hidden.
Putting the pieces together is necessary for all genomes, and we’ve got used to doing this where the genetic code is similar in size to our own, or smaller.
In Genome Research Smith described the 14 axolotl chromosomes, including 94 percent of the axolotl’s genes. It’s the first comprehensive assembly not only of the axolotl genome, but of any genome this size, and includes matching the axolotl genome to those of other species, helping us determine the points in their evolution at which many key changes occurred.
"Just a few years ago, no one thought it possible to assemble a 30+GB genome," Smith said in a statement. "We have now shown it is possible using a cost-effective and accessible method, which opens up the possibility of routinely sequencing other animals with large genomes."
The work relies on the axolotl’s ancestry and the fact stretches of DNA that are inherited together tend to stay close within the genome.
Related species of salamander are sometimes neotenic, meaning they stay in their larval form all their lives, reproducing in that state. This is the equivalent of tadpoles mating and laying eggs without becoming frogs. However, whereas populations of the closely related tiger salamander become neotenic where the land around their waterholes lacks nutrients, axolotl’s are unusual in being exclusively neotenic unless injected with iodine.
Neoteny comes with remarkable powers of regeneration from damage, but axolotls are extreme. As well as being able to regenerate limbs, they can restore internal organs, including hearts and brains, that have been damaged to a point where other animals would never recover. Humans may never match this completely, but the more we understand about how axolotls recover, the better we may be able to do in restoring ourselves.
