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Scientific experts have accomplished the first-ever complete genome sequence of a Greenland shark.(Image credit: dottedhippo via Getty Images)Share this article 0Join the conversationFollow usAdd us as a preferred source on GoogleSubscribe to our newsletter
The inaugural whole-genome sequencing of a Greenland shark has unearthed genetic insights into how these creatures resist cancer and achieve extraordinary lifespans. This research could potentially lead to a deeper comprehension of age-related ailments in humans.
Greenland sharks (Somniosus microcephalus) typically reach lengths of approximately 13 to 16 feet (4 to 5 meters) and inhabit the North Atlantic and Arctic oceans for extended periods. Due to their preference for depths up to 1.65 miles (2.65 kilometers), little is known about these sharks. Estimates suggest they can live for around 400 years and do not attain sexual maturity until approximately 150 years of age, marking them as the longest-living vertebrates discovered to date.
Recent investigations conducted by Shigeharu Kinoshita, a fisheries chemist at the University of Tokyo, alongside his associates, have successfully mapped nearly the entire genome of a Greenland shark — precisely 96.7%. Their study, published on May 19 in the journal PNAS, identified a significant number of genes potentially associated with the sharks’ remarkable longevity.
A crucial discovery involved genetic alterations manifesting as unique amino acid substitutions within “linker histone proteins.” These proteins are responsible for the spooling and compacting of DNA. Such modifications may contribute to the stability of the sharks’ chromatin, which is the complex of DNA and proteins forming chromosomes. This stabilization, in turn, could mitigate the cumulative DNA damage over their exceptionally long lives, as Kinoshita communicated to Live Science via email.
The research team also observed an expansion in gene families associated with immune responses and DNA repair mechanisms within the shark genome. This finding, according to Kinoshita, supports the hypothesis that effective damage repair and immune system regulation are vital for both longevity and cancer immunity.
A third revelation shedding light on the sharks’ longevity was the notable proliferation of ferritin genes, which play a role in iron storage and regulation. This gene expansion suggests an enhanced capacity in the sharks to manage iron metabolism and reduce oxidative stress, a process that can harm DNA and lead to cancer. It might also indicate a restriction of ferroptosis, a form of programmed cell death dependent on iron.
“Our genomic analyses have provided multiple indicators of augmented genome stability and stress resilience in the Greenland shark,” Kinoshita stated. He further elaborated that “Extreme longevity is likely not determined by a single gene, but rather by synchronized changes across various biological systems, including genome stability, iron metabolism, immune function, and stress resistance,” suggesting that this work could offer valuable insights for research into human aging and age-related diseases.
The characteristics linked to improved immunity, cancer resistance, DNA repair, and chromatin stability might elucidate the shark’s extraordinary lifespan, according to Dorota Skowronska-Krawczyk, a physiologist and biophysicist at the University of California, Irvine. Skowronska-Krawczyk recently demonstrated how DNA-repair-associated genes in the retina might contribute to the Greenland shark maintaining clear vision throughout its extended life. “This could be associated with longevity and cancer resistance, but direct testing through functional studies will be necessary,” she remarked, noting her non-involvement in the current research.
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Prior research indicated that the sharks maintain a stable metabolism throughout their lives, which has been proposed as another factor contributing to their remarkable longevity.
Aaron MacNeil, a biologist at Dalhousie University in Nova Scotia who was not part of the study, informed Live Science that the findings align with the notion that these sharks are exceptionally long-lived. However, MacNeil expressed skepticism regarding the 400-year lifespan estimate, which is derived from radiocarbon isotope signatures from Cold War nuclear testing found in the sharks’ eye lenses. The layered growth of these lenses allows researchers to pinpoint the isotope’s location within the layers, providing a temporal marker for age assessment.
The slow circulation of oceanic layers in the frigid depths inhabited by Greenland sharks might delay the dispersal of bomb radiocarbon into the deep sea, potentially leading to an overestimation of the sharks’ age. “Nevertheless, we are certain they are extremely old — at least 200 years,” MacNeil asserted.
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