Scientists have compiled probably the most full genome ever of the Greenland shark, an exceptionally long-lived species. Residing as much as 400 years in all probability has quite a bit to do with superior DNA repair mechanisms.
Methuselahs of the ocean
Greenland sharks, large, slow-moving abyss dwellers, maintain the title of the longest-lived vertebrate. Whereas estimating a wild species’ most lifespan is difficult, Greenland sharks are thought to dwell to about 400, give or take a century [1]. The closest different shark species can get to that’s 100 years, which is already respectable.
Scientists have been finding out Greenland sharks in an try to know the origins of their distinctive longevity. In a brand new paper, at the moment printed as a pre-print that has not but been peer-reviewed, a gaggle of researchers report having compiled probably the most full Greenland shark genome ever. This allowed them to make a number of educated guesses.
Don’t let it break
Identical to the Greenland shark itself, its genome is gigantic and stuffed with repetitive sequences. These account for 70% of the shark’s genome and consist largely of retrotransposons: remnants of retroviruses which have inserted their genetic code into their hosts’ genomes over the eons of evolution. Some retrotransposons are nonetheless in a position to reproduce by copying themselves and inserting new copies again into the genome. Retrotransposon exercise has been linked to a number of hallmarks of ageing [2], and long-lived species should develop methods to mitigate it.
The researchers seen the spectacular conservation of gene order (synteny) between the Greenland shark and different shark species, equivalent to the nice white shark, though they diverged about 250 million years in the past. Once we hear that sharks haven’t modified because the daybreak of time, that’s what it means, genetically. “Total, regardless of an evolutionary distance of a number of hundred million years between them,” the researchers write, “the Greenland shark and the nice white shark present hanging similarities of their genomic construction and group.”
Nonetheless, there nonetheless have to be one thing within the Greenland shark’s genome that makes it dwell 4 occasions longer than every other shark species. Usually, mechanisms that extend lifespan contain gene duplication. For example, elephants have a number of copies of the p53 gene, an important tumor suppressor [3].
When the researchers examined the Greenland shark’s genome for gene duplication, they discovered 81 genes that exist as single copies in all different members of Elasmobranch, a subclass of animals that features sharks and rays, however have a number of copies within the Greenland shark. These genes behave quite a bit like a community and, in keeping with gene ontology evaluation, are associated to double-strand DNA break restore.
Curiously, though p53 seems to behave as this community’s grasp regulator, it exists as a single copy. Nonetheless, that single p53 gene additionally carries a mutation particular to the Greenland shark.
“Taken collectively,” the authors conclude, “duplications of genes related to DNA restore and the p53 pathway seem to differentiate the extraordinarily long-lived Greenland shark from different Elasmobranch species, outlining the trail for added analyses and validations.”
The researchers additionally recognized genes displaying constructive choice, i.e., representing vital evolutionary modifications within the Greenland shark in comparison with intently associated species. Curiously, solely eight such genes have been discovered, which is extra proof that even comparatively minor genetic modifications can facilitate an enormous lifespan extension.
The arms race
The authors hypothesize that what seems to be the Greenland shark’s superior DNA restore capacity could have one thing to do with the abundance of retrotransposons in its genome. Since retrotransposons can themselves trigger double-strand DNA breaks, it’s attainable that retrotransposon exercise precipitated the event of extremely environment friendly DNA restore mechanisms in type of an arms race.
The researchers made the Greenland shark’s genome and troves of associated information out there to everybody through a dedicated genome browser. This implies you can attempt your luck in discovering different attainable mechanisms that enable this superb animal to survive people by an element of 4.
The enlargement of retrotransposon sequences in each species contributed considerably to the elevated genome sizes. Within the case of the GLS, we’ve got offered proof that this mechanism could have contributed to the enlargement of DNA restore gene sequences. On condition that retrotransposons themselves are a supply of double-strand breaks (Warkocki 2023), our findings counsel that the evolution of DNA restore genes and retrotransposons could also be interlinked within the GLS. Particularly, retrotransposon exercise could have led to the enlargement of DNA repair-associated retrogenes, which, in flip, allowed for the tolerance of upper retrotransposon exercise.
Literature
[1] Nielsen, J., Hedeholm, R. B., Heinemeier, J., Bushnell, P. G., Christiansen, J. S., Olsen, J., … & Steffensen, J. F. (2016). Eye lens radiocarbon reveals centuries of longevity within the Greenland shark (Somniosus microcephalus). Science, 353(6300), 702-704.
[2] Gorbunova, V., Seluanov, A., Mita, P., McKerrow, W., Fenyö, D., Boeke, J. D., … & Sedivy, J. M. (2021). The position of retrotransposable components in ageing and age-associated illnesses. Nature, 596(7870), 43-53.
[3] Abegglen, L. M., Caulin, A. F., Chan, A., Lee, Okay., Robinson, R., Campbell, M. S., … & Schiffman, J. D. (2015). Potential mechanisms for most cancers resistance in elephants and comparative mobile response to DNA injury in people. Jama, 314(17), 1850-1860.
