The secret of turtle longevity
The genome of Lonely George told about the longevity of giant turtles
Ekaterina Rusakova, N+1
The genomes of giant turtles, including Lonely George, told about the secret of the longevity of these animals. As described in Nature Ecology&Evolution, these reptiles turned out to have more copies of genes that are part of the innate immunity system than mammals. They also acquired additional copies of genes or developed mutations in genes that affect aging processes, in particular, those involved in DNA repair.
Lone George was nicknamed the male Abingdon elephant turtle (Chelonoidis abingdonii), a subspecies endemic to the Galapagos island of Pinta. George turned out to be the last representative of the Abingdon turtles, which became extinct due to habitat loss. Since the early 1970s, Lonely George lived in the Charles Darwin Research Center, where they repeatedly tried to get offspring from him, but without success. In 2012, the turtle died at the age of about 100 years and the subspecies finally became extinct.
Abingdon elephants, like other giant turtles, are long-lived. According to some estimates, the average life expectancy of giant turtles is about 100 years. Geneticists from five countries, led by Adalgisa Caccone from Yale University and Carlos Lopez-Otin from the Spanish University of Oviedo, decided to analyze the genomes of giant turtles to clarify their evolutionary history and find genes that affect the size and longevity of these animals. Researchers have sequenced the genome of Lonely George and the gigantic (or Seychelles giant) turtle Aldabrachelys gigantea – endemic to the island of Aldabra. The representative of this species, the male Jonathan, is now the oldest living land animal, he is approximately 186 years old. Also, based on homology with reference genomes (human and Chinese trionyx Pelodiscus sinensis), the authors identified genes associated with immunity, regulation of metabolism and control of aging processes in giant turtles.
It turned out that the last common ancestor of Seychelles giant and Abingdon elephant turtles lived about 40 million years ago, and the ancestors of giant turtles and humans separated about 312 million years ago. Researchers have found in giant turtles additional copies of the genes H1, CAMP, CHIA and NLRP, which are associated with protecting the body from parasites, viruses, fungal and bacterial infections, compared to mammals. Perhaps the innate immunity in giant turtles plays a greater role than in mammals. Giant turtles also had an increased number of copies of the GAPDH gene encoding glyceraldehyde-3-phosphate dehydrogenase, an enzyme involved in DNA repair, apoptosis and energy synthesis in cells. At the same time, they did not have the NLN gene functioning. The loss of this gene in mice increased their sensitivity to insulin and improved glucose uptake.
Long-lived organisms theoretically increase the likelihood of getting cancer. To protect themselves from cancer, giant turtles have acquired additional copies of genes responsible for suppressing the growth of malignant tumors and strengthening the immune response.
Finally, the authors of the study identified 468 genes in giant turtles involved in the control of aging processes, in particular, genes that affect the integrity of the genome and are involved in various DNA repair systems. For example, scientists have discovered in giant turtles a single mutation in the XRCC6 gene, which encodes an enzyme involved in connecting the ends of "broken" DNA. Other vertebrates do not have such a mutation. The only exception is the naked digger, a long–lived rodent whose life expectancy reaches 32 years.
Previously, researchers have found out how large nocturnal bats became long-lived. They have learned to maintain the length of telomeres, the DNA sections at the ends of chromosomes that ensure DNA copying during cell division. A decrease in telomere length is considered one of the causes of aging.
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