A team of researchers from NSU’s Save Our Seas Foundation Shark Research Center (SOSSRC) and Guy Harvey Research Institute (GHRI), Cornell University College of Veterinary Medicine and Monterey Bay Aquarium, decoded the complete genome of the great white shark and compared it to the genome of other model organisms.
“The idea was to look for things that were unique within the shark genome and things that were shared between the shark and other vertebrates, including a whale shark,” said Mahmood Shivji, director of Save Our Seas Shark Research Center and Guy Harvey Research Institute at NSU.
This research project contributed to three major findings: a large genome, LINEs elements or an abundance of jumping genes and positive selection, as well as enrichment in wound healing pathways.
“The genome is about one and a half times the size of the human genome. In addition to that, we looked to see what might explain this very large genome, all this additional DNA. We found that a white shark has a lot of repeated DNA sequences. That in itself is not surprising, but what was surprising is that of all these repeated DNA sequences there were about 30 percent of LINEs elements. These [LINEs elements or jumping genes] have the ability to make copies, move around and insert themselves in different parts of the genome. To do this, they have to break the DNA first or make what is known as double-stranded DNA breaks. They do this by breaking the DNA, inserting themselves within the breaks and then sealing those breaks,” said Shivji.
The process of breaking and resealing DNA can generate mistakes in the sequence during the sealing process. This can cause many problems in the genome such as mutations that can cause genome instability.
“Genome instability is an important biological phenomenon. In humans, an individual’s DNA with genome instability has a lot of mutations and breaks which can cause cancers and other age-related diseases. There is a huge interest in the medical research world to try and figure out how to reduce genome instability in human and reduce instances of disease. We saw that there was a lot of jumping genes in the white shark DNA which would indicate that the genome was unstable. But on the other hand, our second discovery found that a lot of the white shark genes have also undergo positive selection,” said Shivji.
Positive selection, in reference to this genome, is changes in the DNA sequence that provide advantages to the organism such as DNA repair, damage response and tolerances. These genes are involved in maintaining genome stability in an organism. This could be considered a counteractive force to having all these jumping genes creating mutations in the genome.
Shivji explained that the research found that other than a link to genome stability, a lot of these positively selected genes were enriched compared to other organisms. These enrichments in the whale shark and white shark were involved in known wound healing pathways similar to the model systems like humans and mice. So it is assumed through these findings, that sharks have advancements in wound healing through the genome.
It is important to point out, however, that although this research may prove that sharks have advancements in their DNA for protective countermeasures to certain ailments, that does not mean that sharks aren’t susceptible to things like cancer.
“Sharks have these amazing adaptations— which is what we found through this study— but that doesn’t mean that eating sharks will cure cancer. Thinking that eating sharks will cure cancer or make your wounds heal faster is about as silly as thinking that eating sharks will make you hold your breath better underwater or swim faster,” said Shivji.
The next thing that the researchers would like to explore is to see if this genome stability and positive selection genes and wound healing in the genome are just restricted to these larger species like the whale shark or white shark, or if these adaptations are seen in all sharks. Further down the line, they would like to investigate if they can bring these shark genes into human model cell lines in the lab and see if these genes can prevent or protect from genome instability.
“There is a general suspiscion— but no hard-core scientific evidence— that sharks have a higher resistance to cancers. Our data supports that idea, that they have a way to keep their genome stable and have less instances of that happening. It can be seen as a type of protective mechanism to prevent cancers or other diseases,” said Shivji.
For more information on this research, the findings are reported in the ‘Latest Articles’ section of the journal Proceedings of the National Academy of Sciences, USA.
