The Greenland shark (Somniosus microcephalus) is the longest-lived vertebrate known, with an estimated lifespan of about 400 years. It roams the North Atlantic and Arctic oceans with a top speed of less than 1.9 miles per hour and a growth rate of under 0.4 inches per year.

The Greenland shark has 6.45 billion DNA bases, which is roughly twice as many as in humans and the biggest set of genes of any other shark sequenced so far. Scientists have finally sequenced the Greenland shark’s genome (a complete set of DNA) to discover the sharks’ 22,634 protein-coding genes with 20,274 genes functionally annotated. 

How does this shark live for so long?

Firstly, scientists identified 81 exclusively duplicated genes found in multiple copies in the Greenland shark, whereas these genes are only present in one copy for all other elasmobranchs (sharks, skates, and rays). In fact, 70.6% of this shark’s genome (complete set of DNA) is composed of repeated genes; that’s hundreds of thousands of repeated genes!

These repeated genes form an exclusive network that codes for proteins specializing in DNA repair and tumor suppression.

Essential Genes in this Network:

1. TP53 gene - This gene codes for the well-known tumor-suppressor protein p53. A study found that species with higher lifespans have particular amino acid substitutions in p53’s DNA-binding area, i.e. the part of the protein that attaches to the TP53 gene is changed. This affects the rate at which genes are being expressed to synthesize new proteins.

2. RAD51 gene - This duplicated gene codes for a protein that improves DNA repair and replication. A 2017 study also discovered RAD51’s role in the body’s innate immune response signaling, because defects in RAD51’s protein have led to an immune response as a result of inevitable DNA damage and replication stress. Three copies of the RAD51 gene were found in Greenland sharks.

People first discovered this shark’s longevity during a 2016 study on the age of 28 female Greenland sharks published in the Science journal, which used radiocarbon dating of eye lens nuclei (places where genetic information is stored) and knowledge of natural events to accurately estimate the ages of the sharks—the oldest one being nearly 400 years old! The eye lens nuclei were used because they are made up of crystalline proteins that aren't involved in the organism’s metabolic processes (chemical reactions necessary for life). These proteins are also developed before birth so they remain in sharks.

In total scientists found eight genes that went through significant evolutionary changes in the Greenland shark compared to other sharks. Surprisingly, seven out of these eight genes were connected to the regulation of aging or minimizing the risk of age-related disease.

These are those seven genes with the eighth gene, excluding TP53 described above:

1. PARP14  - Has many functions including the control of transcription (coding of DNA into mRNA to be converted into proteins) and DNA replication.

2. MRPS35 - Balance of proteins in nuclear and mitochondrial DNA.

3. ZCCHC17 - Regulates which neuronal (nerve cell) genes are activated or deactivated and thus controls protein production for nerve cells. They also provide resistance against developing Alzheimer’s disease.

4. TRAPPC8 - Regulates the destruction of damaged or non-functional cells which occurs in the cell (autophagy).

5. DDX42 - Regulates a large protein molecule that removes components of mRNA that do not code for proteins and joins coding sections of RNA together (spliceosome).

6. DESI1 - Maintains regulation of T cells (a type of white blood cell) which regulates the immune system.

7. ACKR3 - Regulates small proteins that resist age-related deterioration.