Is there a more daunting animal to study than the great white shark? It’s an iconic apex predator, one of the most fearsome fish in the sea. Now scientists know just what it’s made of and it may hold the key to discovering a cure for cancer.
Scientists said Monday they have decoded the genome of Earth's largest predatory fish, detecting numerous genetic traits that help explain its remarkable evolutionary success, including molecular adaptations to enhance wound healing as well as genomic stability such as DNA repair and DNA damage tolerance.
The great white shark, whose scientific name is Carcharodon carcharias, genome is one-and-a-half times bigger than that of a human and contains a plethora of mutations that protect against cancer and other age-related diseases. Experts believe the great white genome evolved to be stable and disease resistant and could be key in developing future treatments.
Sharks have been around a long time. Scientists estimate that they’ve stalked the oceans for some 400 million years ago, well before the first adventurous amphibians left the oceans for dry land (For comparison, great apes have existed for something like 20 million years.) Surviving that long isn’t easy. Scientists at Nova Southeastern University, Clemson University, and elsewhere wanted to find out how sharks have done it.
In theory, large genomes with a lot of repeated DNA, like this shark possesses, and its large body size should promote a high incidence of genome instability, with much more DNA and many more cells seemingly vulnerable as targets for damage through an accumulation of routine mutations.
Just the opposite seems to be the case for this shark, thanks to adaptations in genes involved in preserving genome integrity.
Repetitions of specific DNA sequences within the shark’s genes indicated molecular adaptation which is essential in protecting DNA against damage. The repetitive sequences were found in genes linked to DNA repair. Together these adaptations have acted to keep the shark's genome stable.
At the same time the great white genome contained high numbers of so-called 'jumping genes', or transposons - short DNA sequences that leap from one location in the genome to another and help speed up evolution.
The research was published in the journal Proceedings of the National Academy of Sciences.
Evolution of the shark ~ Image credit: Smithsonian
“Decoding the white shark genome is providing science with a new set of keys to unlock lingering mysteries about these feared and misunderstood predators – why sharks have thrived for some 500 million years, longer than almost any vertebrate on earth,” said Salvador Jorgensen, a co-author of the study.
Other great white gene mutations were found to be linked to processes involved wound healing, including blood clotting. Sharks are known for their impressive ability to recover from even serious injuries.
As sharks evolved so long ago, and so far away from humans on the tree of life, it’s possible that these genes represent totally novel anti-cancer defenses. The incidence of cancer in wild sharks is poorly understood, so the scientists plan to test the hypothesis in the lab. By splicing genome-stabilizing shark genes into transgenic mice and then exposing the rodents to well-known carcinogens, they hope to measure the protective powers of shark DNA.
"This knowledge, in addition to providing understanding into how sharks work at their most fundamental level — their genes — may also be useful in downstream applications to human medicine to combat cancers and age-related diseases that result from genome instability," said Mahmood Shivji
Further reading: SHARKS!10 FACTS ABOUT GREAT WHITE SHARKS!