The genomes of giant turtles, including Lonesome George, told about the secret of longevity of these animals. As described in Nature Ecology & Evolution , these reptiles turned out to have more copies of the 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, involved in DNA repair.
The lonely George was nicknamed the male of the Abingdon elephant turtle ( Chelonoidis abingdonii ), a subspecies endemic to the Galapagos island of Pinta. George was the last representative of the Abingdon turtles, which became extinct due to the disappearance of the habitat. Since the early 1970s, Lonely George lived at the Charles Darwin Research Center, where he was repeatedly tried to get offspring, but to no avail. In 2012, the turtle died at the age of about 100 years and the subspecies finally died out.
The Abingdon elephantfish, like other giant tortoises, are long-livers. According to some estimates, the average lifespan of giant turtles is about 100 years. Genetics from five countries under the leadership of Adalgisa Caccone from Yale University and Carlos López-Otin from Spanish University of Oviedo decided to analyze the genomes of giant turtles to clarify their evolutionary history and find genes that affect their size and longevity these animals. Researchers have sequenced the genome of Lonely George and the giant (or Seychelles giant) tortoise Aldabrachelys gigante a – endemic to Aldabra Island. A representative of this species, the male Jonathan, is now the oldest living land animal, about 186 years old. Also, based on homology with reference genomes (human and Chinese trionix Pelodiscus sinensis), theauthors identified in giant skulls genes associated with immunity, regulation of metabolism and control of aging processes.
It turned out that the last common ancestor of the Seychelles giant and Abingdon elephant turtles lived about 40 million years ago, and the ancestors of giant turtles and people separated about 312 million years ago. Researchers have found additional copies of APOBEC1 , CAMP , CHIA andNLRP genes associated with protecting the body against parasites, viruses, fungal and bacterial infections in giant turtles, compared with mammals . Perhaps innate immunity in giant turtles plays a greater role than in mammals. Also, giant tortoises have an increased number of copies of the GAPDH gene.encoding glyceraldehyde-3-phosphate dehydrogenase – an enzyme involved in DNA repair, apoptosis and in the synthesis of energy in cells. At the same time, the NLN gene was not functioning in them . The loss of this gene in mice increased their insulin sensitivity and improved glucose uptake.
In organisms long-lived theoretically increases the likelihood of cancer. To protect against cancer, giant turtles have acquired additional copies of the genes responsible for suppressing the growth of malignant tumors and enhancing the immune response.
Finally, the authors of the study identified 468 genes 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 a single mutation in giant turtles in the XRCC6 gene , which encodes an enzyme that is involved in connecting the ends of “torn” DNA. The remaining 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 figured out how bats great moths became long-livers. They have learned to maintain the length of telomeres, DNA segments at the ends of chromosomes, which ensure DNA copying during cell division. Reducing the length of telomeres is considered one of the causes of aging.
Lonely George is not the only known male of the Galapagos turtles. Prior to that, we wrote in detail about a representative of another subspecies, the 100-year-old male Diego.