The researchers now plan to make a gene chip designed to detect levels of some of these candidate genes, so that the scientists can determine at exactly what point during the regeneration process the genes are turned on. The team is also developing molecular tools that allow them to silence specific genes, which will enable them to pinpoint those that are crucial for proper regrowth.
Scientists also sequenced random chunks of the salamander genome. At about 30 billion bases and 10 times the size of the human genome, it is one of the largest among vertebrates. Most scientists expected that the extra DNA would be made up of junk DNA, long stretches of bases between genes. But initial findings were surprising. “Genes are on average 5 to 10 times larger than those in other vertebrates,” says Voss. “The region of the genome containing genes is estimated to be more than two gigabases, which is as big as some entire genomes.”
The extra DNA sequences sit within genes and are cut out during the translation from gene to protein. Much of this DNA comprises repetitive sequences not found in any other organisms to date, says Pao. However, it’s not yet clear whether these repetitive stretches help facilitate regeneration or play some other role in the salamander’s life cycle.
One of the key questions yet to be answered is whether the salamander has unique genetic properties that enable regeneration, or whether all animals have that innate capability. “If we come up with some totally unique gene only present in axolotl, that would make it really hard to replicate,” says David Gardiner, a biologist at the University of California, Irvine, who is also collaborating on the project. He prefers to think that regeneration comes from a fundamental abilitylying dormant in mammals, which could be reawakened with some simple genetic prodding.”Most of the tissue in our arm regenerates; it’s just the arm that doesn’t regenerate,” he says. “What’s missing is how you coordinate a response to get an integrated structure.”