The Greenland shark genome

Greenland sharks are growing at an extremely fast rate slow pace less than 1 centimeter (0.4 inch) per year but can eventually reach more than 6 meters (about 20 feet) in length, and they do not reach sexual maturity until they are over a century old. It is suspected that the oldest species could survive for more than half a millennium.

The study authors found that the shark’s genome was extraordinarily large, twice as long as that of humans and larger than any other shark genome sequenced to date. Researchers are analyzing the genome to explore what its large size may mean for the shark’s longevity. One reason for a longer genome may be due to the shark’s ability to repair its DNA, a trait commonly seen in other exceptionally long-lived species, including the naked mole-rat, the longest-lived rodent that can live up to 30 years or more. more, and certain species of turtles which can live to be over 100 years old.

The Greenland shark is unique in that a large portion – more than 70% – of its genome is made up of skipping geneswhich can move within the DNA sequence by duplicating themselves, sometimes creating mutations. Often, these duplications are referred to as genetic parasites because of their potential harmful effects, particularly on genetic diseases such as cancer.

However, it appears that in the Greenland shark, genes that repair DNA act like jumping genes, distributing themselves throughout the genome and slowing the aging process by repairing damaged DNA. As a result, “the detrimental effect of these transposable elements (jumping genes) is not only negated, but perhaps even reversed, so that genome integrity is even better in the Greenland shark,” said the lead author Dr. Arne Sahm, bioinformatician. and junior professor at Ruhr University Bochum, Germany.

The authors suggest that the species’ DNA repair genes at some point evolved the ability to multiply, thereby contributing to DNA repair and, therefore, longevity. Researchers want to further explore and analyze the Greenland shark’s DNA, while comparing its genome with other shark species and shorter-lived fish, to provide additional evidence for this unique trait, Hoffman said.

Study the Greenland shark

Before researchers sequenced the Greenland shark genome, only about 10 genomes were available for all elasmobranchs – a subclass of fish including sharks, rays and skates – said Dr Nicole Phillips, associate professor of in ecology and organismal biology at the University of Southern Mississippi. in Hattiesburg. Phillips was not involved in the research conducted by Hoffman, Sahm and their team.

“The more high-quality genomes are sequenced, the better we can understand the genetic underpinnings of the common and unique traits of this ancient group,” Phillips said in an email. “Identifying the genetic basis of lifespan in different species, including long-lived sharks, allows researchers to understand the biology of aging and longevity.”

Due to the sharks’ preference for deep waters, most information on the Greenland shark historically came from commercial fishing records. Over the past decade, researchers have increasingly used video, including remotely operated vehicles and baited cameras, as well as sightings of captured specimens to study this elusive shark.

To sequence and study the shark’s genetic makeup, the authors euthanized several specimens to obtain a tissue sample, for which they had a research permit. But scientists hope their work on the Greenland shark genome will ultimately contribute to the conservation of the species, Hoffman said. The Greenland shark is currently listed as vulnerable on the International Union for Conservation of Nature Red List of Threatened Species, with its last assessment in June 2019.

“The authors were able to gain insight into an animal that truly occupies a unique place in the evolutionary tree of life. “It’s very ancestral and so it could represent, at least in sharks, potentially how all genomes evolved, because it provides this snapshot of a really interesting and very specialized genome,” said Dr. Toby Daly. Engel, associate professor of ocean sciences. engineering and marine science at the Florida Institute of Technology in Melbourne and director of the Florida Tech Shark Conservation Lab. Daly-Engel was not involved in the research.

“On the one hand, I think understanding these jumping genes is really interesting, and yet on the other hand, it’s not surprising that they’re seeing things that we’ve never seen before,” she added, “because even though we have sequenced other shark genomes, shark species are so different from each other that we can expect new things with each species.

In previous research, scientists have been able to extend the lifespan of some short-lived species, like flies and mice, using genetic modifications. By searching for longer-lived species, scientists can better understand the aging process across species and the toolkits that could potentially be applied to extend human lifespan, Sahm said.

“Evolution does not always choose the same path. So if, say, the goal is to have better DNA repair, but this can be achieved by multiple mechanisms, and the mechanisms are different in mole rats, whales and sharks, we need to learn about each of them and then see which ones. perhaps we can more easily adapt for human use,” said Dr. Vera Gorbunova, professor of medicine and biology at the University of Rochester in New York and lead author of a 2023 study which used transferred naked mole-rat genes to extend the lifespan of mice. Gorbunova was not involved in the Greenland shark research.

“Once researchers understand the mechanism…we can then see if we can design a specific drug to target this enzyme in the genome in this way,” she added. “You can dream of gene therapy, maybe we could give people a gene from the Greenland shark, but that might be a more science fiction type approach, but something more easily translatable would be, well , maybe we could design a drug that targets (a) the human gene and makes it work a little more like a Greenland shark’s and that would improve… DNA repair in humans.

Many environmental influences damage human DNA, such as sunlight or smoking. By learning more about the Greenland shark’s unique DNA repair technique, scientists can begin to study how this trait contributes to other age-delaying factors, such as suppressing tumors in the shark’s cells. from Greenland, as well as its potential effects on the cells of other species, including our own. , Sahm said.

“If we really want to increase human lifespan significantly, or maybe even better, extend the percentage of our lives (in which) we are actually healthy and fit and can do things… it’s It’s good to look at tips from very long years. lived animals,” he added, “how they change their system as a whole, what strategies they use and then learn from…those strategies.” »