The Greenland shark, a creature of the deep, has long been a subject of intrigue due to its elusive nature and remarkable longevity. These slow-moving predators inhabit the frigid depths of the North Atlantic and Arctic Oceans, uniquely adapted to withstand the extreme cold throughout the year. It is believed that some individuals of this species have been navigating these waters since the colonial era, and scientists are now beginning to uncover the secrets behind their astonishing lifespan. With a metabolism so slow that it was long suspected to be linked to an extended life, the Greenland shark's exact age was a mystery until recent research in 2016 revealed it to be the longest-living vertebrate, with an estimated lifespan of around 400 years, ranging from 272 to over 500 years. Now, a new study aims to unravel the biological mechanisms behind this extraordinary longevity.

An international collaboration of scientists has achieved a groundbreaking milestone by mapping the genome of the Greenland shark, successfully sequencing approximately 92% of its DNA. This genetic blueprint provides valuable insights into the internal workings of these long-lived marine animals. The genome assembly, a computational representation of the shark's genetic makeup, not only enhances our understanding of the shark's structure and physiological functions but also offers clues to the factors contributing to their remarkable longevity, according to the researchers.

"The genome assembly is a crucial tool that allows us and other researchers to delve into the molecular mechanisms behind the shark's extended lifespan," explained Dr. Steve Hoffman, the senior author of the new research on the Greenland shark and a computational biologist at the Leibniz Institute on Aging in Germany. "It helps us identify mutations that have accumulated in the shark, leading to this extraordinary lifespan."

The study's findings have been released as a preprint, a scientific paper that has yet to undergo peer review, inviting further scientific scrutiny and analysis of the shark's DNA. There are only a handful of animal species that outlive humans, especially when considering body weight and size. By examining the longevity mechanisms of the Greenland shark, scientists hope to gain insights that could potentially inform efforts to extend human lifespan.

The Greenland shark's genome is notably large, twice the length of a human's and surpassing any other shark genome sequenced to date. Researchers are investigating the implications of this large genome size for the shark's longevity. One hypothesis is that the shark's capacity to repair its DNA, a trait observed in other long-lived species such as the naked mole rat and certain tortoise species, may be a contributing factor.

The Greenland shark's genome is also distinguished by the high proportion of transposable elements, or "jumping genes," which make up over 70% of its genetic material. These elements can duplicate themselves and move within the DNA sequence, sometimes leading to mutations. Typically, these duplications are considered genetic parasites due to their potential to cause harm, including genetic diseases like cancer. However, in the Greenland shark, it appears that DNA repair genes have evolved to act as jumping genes, distributing themselves throughout the genome and slowing down the aging process by repairing damaged DNA.

"The negative effects of these transposable elements are not only neutralized but may even be reversed, enhancing the genome integrity in the Greenland shark," stated lead author Dr. Arne Sahm, a bioinformatician and junior professor at Ruhr University Bochum in Germany. The researchers propose that the DNA repair genes in the Greenland shark have evolved the ability to multiply, further enhancing DNA repair and contributing to longevity.

The team plans to further analyze the Greenland shark's DNA and compare its genome with other shark species and shorter-lived fish to provide additional evidence for this unique trait. Prior to the sequencing of the Greenland shark's genome, only about 10 genomes were available for elasmobranchs, a subclass of fish that includes sharks, rays, and skates, according to Dr. Nicole Phillips, an associate professor of ecology and organismal biology at the University of Southern Mississippi in Hattiesburg, who was not involved in the research.

"Sequencing more high-quality genomes allows us to better understand the genetic foundations of both shared and unique traits within this ancient group," Phillips said. "Identifying the genetic basis of lifespans across different species, including long-lived sharks, helps researchers understand the biology of aging and longevity."

Due to the Greenland shark's preference for deep waters, most historical information about the species came from commercial fishing records. Over the past decade, researchers have increasingly utilized video footage, including remotely operated vehicles and baited cameras, as well as observations from captured specimens to study this elusive shark. To sequence and study the shark's genetic makeup, the researchers obtained tissue samples from several specimens, for which they had a research permit.

The scientists hope that their work on the Greenland shark genome will ultimately contribute to the species' conservation efforts. The Greenland shark is currently listed as vulnerable on the International Union for Conservation of Nature's Red List of Threatened Species, with its last assessment in June 2019.

"The authors have gained insight into an animal that occupies a unique position in the evolutionary tree of life. It is very ancestral and could potentially represent how all genomes evolved in sharks, as it provides a snapshot of a very specialized genome," said Dr. Toby Daly-Engel, an associate professor of ocean engineering and marine sciences at the Florida Institute of Technology in Melbourne and director of the Florida Tech Shark Conservation Lab, who was not involved with the research.

In previous studies, scientists have managed to extend the lifespan of certain short-lived species, such as flies and mice, through genetic modifications. By studying more long-lived species, scientists can gain a better understanding of the aging process across all species and the potential tools that could be applied to prolong human lifespans, according to Dr. Vera Gorbunova, a professor of medicine and biology at the University of Rochester in New York and the lead author of a 2023 study that used transferred naked mole rat genes to extend the lifespan of mice.

"Evolution does not always follow the same path. If the goal is to improve DNA repair, it can be achieved through multiple mechanisms, and these mechanisms vary across mole rats, whales, and sharks. We need to learn about all of them and then determine which ones we can more easily adapt for human use," Gorbunova said. "Once researchers understand the mechanism, we can consider designing a specific drug to target this genome enzyme in a similar way. While gene therapy or transferring genes from the Greenland shark to humans might be more of a science-fiction approach, a more feasible option could be designing a drug that targets a human gene to function more like that of a Greenland shark, thereby improving DNA repair in humans."

There are numerous environmental factors that can damage human DNA, such as sunlight exposure or smoking. By learning more about the Greenland shark's unique DNA repair technique, scientists can begin to investigate how this trait contributes to other age-delaying factors, such as tumor suppression in Greenland shark cells and potential effects on the cells of other species, including humans, according to Sahm.

"If we truly want to significantly increase human lifespan, or even better, to extend the proportion of our lives in which we are healthy, fit, and capable, it is beneficial to examine the strategies employed by very long-lived animals, how they alter their systems overall, and then to learn from those strategies," he added.