Shark DNA may hold clues to human cancer treatment

Scientists who have decoded the great white shark genome for the first time may have uncovered clues which could help develop human cancer treatments.

Shark DNA has evolved to be more stable and tolerant to damage than human DNA, according to the international team, led by researchers in Nova Southeastern University (NSU) in Fort Lauderdale, Florida.

'Genome instability is a very important issue in many serious human diseases,' said Dr Mahmood Shivji at NSU, who co-led the study. 'Now we find that nature has developed clever strategies to maintain the stability of genomes in these large-bodied, long-lived sharks.'

Dr Shivji and his team noticed numerous positive or 'adaptive' changes in the DNA sequences of genes known to be involved in genetic stability, including DNA repair genes.

They also noticed an unusually high abundance of genetic sequences called LINEs. These are 'jumping genes'  or 'transposable elements' that move around the genome and can create mutations. These can be useful for genetic diversity, or harmful, with the potential to lead to cancer.

With this preponderance of LINEs, their large body size and their longevity at lifespans of about 70-years, these sharks should be at a greater risk of genetic mutations, and therefore cancer.

Large-bodied animals like whales and elephants are expected to get more cancers than humans, but this is not the case. In 2018, research at the University of Chicago in Illinois, indicated that elephants were able to utilise a dormant tumour suppressor gene (see BioNews 963). This has contributed towards explaining the paradox of why larger animals do not have an increased chance of acquiring cancer. 

The team combined the DNA from samples from two great white sharks to create an entire genome with 41 pairs of chromosomes. The research also found that the shark's genome is one and half times the size of the human genome, at about 4.6 billion base-pairs of DNA. 

Dr Shivji said: 'There's still tons to be learned from these evolutionary marvels, including information that will potentially be useful to fight cancer and age-related diseases, and improve wound healing treatments in humans, as we uncover how these animals do it.'

It is hoped that the genome will also 'assist with the conservation of great whites and related sharks, many of which have rapidly declining populations due to overfishing', said study co-author Dr Stephen O'Brien, a conservation geneticist at NSU.

The study was published in PNAS.