The secret of a long life
Geneticists explained the longevity of white sharks
Ekaterina Rusakova, N+1
White shark (Carcharodon carcharias) It feeds on carrion in the Bay of Falls Bay, South Africa (Hammerschlag et al., PLoS ONE, 2013).
Geneticists have collected the white shark genome for the first time, according to the Proceedings of the National Academy of Sciences. Scientists have found in it the genes of proteins responsible for maintaining the stability of the genome, which is associated with the aging process. Perhaps the presence of these genes can explain the longevity of white sharks. Also, genes associated with rapid wound healing were found in their DNA.
Cartilaginous fish are one of the oldest groups of vertebrates; they appeared about 400 million years ago. One of the most recognizable representatives of the class is the white shark (Carcharodon carcharias). The length of these fish can reach six meters, and the weight reaches almost two tons. The study of the genome of these fish is interesting to scientists for several reasons. These are some of the longest–lived cartilaginous fish - according to scientists, their maximum life expectancy reaches 73 years. White sharks are able to withstand large temperature changes, in particular, to dive to a depth of over a kilometer. They smell prey and can determine the source of the smell by changing the concentration of the aromatic substance. Finally, they have the secret of rapid wound healing.
American, Russian and Portuguese researchers led by Mahmood S. Shivji from the Southeastern University of Nova collected the genome of a high-quality white shark (with 198-fold coverage), analyzed it and compared it with the known genomes of other cartilaginous fish – the whale shark (Rhincodon týpus) and a representative of the order of chimeras of the Australian callorhinchus (Callorhinchus milii). It is also called the elephant shark.
The authors found in the DNA of white sharks genes of proteins responsible for maintaining the stability of the genome and for the rapid healing of wounds. The genome of these fish turned out to be about one and a half times longer than the human genome (4.65 billion and 3.23 billion base pairs, respectively). The total number of genes in the shark genome is approximately 24.5 thousand. The researchers recognized at least 67 genes responsible for the stability of the genome, that is, for maintaining mutations in DNA at a low level. Among them were genes of enzymes involved in DNA repair, suppression of tumor growth and apoptosis – programmed cell death, as a result of which defective cells are destroyed. The stability of the genome, in turn, is associated with aging. It is believed that its cause is the gradual accumulation of mutations in the body that can lead to the development of cancer, "breakdown" of cells or their death. Therefore, perhaps the stability of the genome of white sharks can explain their longevity.
The researchers also found three loci in the genome of white sharks, probably associated with rapid wound healing. They contained the gene of one of the subunits of the fibrinogen protein (FGG), the main component of clots formed during blood clotting. The EXTL2 gene encodes one of the enzymes necessary for blood clotting and the formation of new blood vessels. This process is called angiogenesis and is activated, among other things, during the regeneration of damaged tissues. Finally, the KRT18 gene encodes one of the keratins, proteins that provide mechanical protection against damage, and some of them play an important role in wound healing.
Despite the fact that the white shark, like other shark species, finds prey by smell, researchers have not found a large number of olfactory receptor genes in the genome. However, neither the whale shark nor the Australian callorhynchus can boast of their abundance. Therefore, the authors decided that, for example, the vomeronasal organ, which is present in some vertebrates and belongs to the additional olfactory system, may be responsible for the sense of smell in sharks. In particular, they found 13 copies of type 2 vomeronasal receptor genes in the white shark genome. They belong to the olfactory class and, presumably, with their help, animals recognize pheromones and other volatile aromatic substances. Whale sharks turned out to have 10 copies of vomeronasal receptor genes, and kallorynchus, as the authors of another study found out, had more than 30. From this, scientists concluded that vomeronasal receptors may be responsible for the acute sense of smell of sharks.
White sharks are among the longest-lived cartilaginous fish. The representative of the shark superorder, the Greenland shark, turned out to be the longest-lived vertebrate known to date. According to the researchers, the average life expectancy of these animals is 272 years, and they reach sexual maturity at about 150 years.
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