The secret that helps Greenland sharks live up to 400 years

Greenland shark (Dreamy microcephalus), a deep-sea hermit in the North Atlantic and Arctic Oceans, is one of the few vertebrates with an estimated lifespan of around 400 years. An international team of researchers from the Leibniz Institute for Aging, the Fritz Lipmann Institute in Jena, the Ruhr University Bochum, the SNS, the University of Copenhagen, and the CNR-IBF Pisa, in collaboration with several other institutes, sequenced the genome of this shark. They published the first results in a database bioRxiv. Data suggests that the Greenland shark’s ability to repair its own DNA may explain its impressive longevity.

The Greenland shark genome is a key step toward understanding the molecular mechanisms of aging in this extremely long-lived species, says Steve Hoffmann, a computational biologist and research leader at the Leibniz Institute for Aging. Only a few complex animals have outlived humans, such as the 191-year-old giant tortoise named Jonatha, who lives on the island of St. Helena. But that record pales in comparison to the Greenland shark.

The size of the shark genome was one of the project’s early challenges. At 6.5 billion base pairs, the Greenland shark’s genetic code is twice as long as that of humans and the largest of any shark genome sequenced to date. Like the axolotl and lungfish, the Greenland shark’s genome is enormous largely due to the presence of repetitive, self-replicating elements. Such transposable elements, sometimes called jumping genes or selfish genes and often considered parasitic, make up more than 70 percent of the Greenland shark genome.

Jumping genes can disrupt the cohesion of other genes and reduce genome stability. However, in the case of Greenland sharks, the high rate of repeated genes does not appear to limit lifespan. Instead, Sahm and his colleagues suspect that the proliferation of transposable elements may contribute to the sharks’ extreme longevity. Sometimes, genes that are more functionally fit can take advantage of the molecular machinery encoded by transposable genes to replicate. Many of the duplicated genes are involved in repairing DNA damage.

The team also found a particular change in p53, nicknamed the “guardian of the genome.” p53 acts as a control center for the response to DNA damage in humans and many other species. The protein is mutated in about half of human cancers and is the most important tumor suppressor. It is therefore an essential gene for longevity, according to Steve Hoffmann. However, further research will be needed to prove that the observed changes in the key gene contribute to the Greenland sharks’ longevity.