World's longest-living dog cancer sequenced

Source:Xinhua Published: 2014-1-24 8:27:34

Researchers from Britain, Australia and Brazil have sequenced the genome of the world's oldest continuously surviving cancer, a transmissible genital cancer that affects dogs.

The results, published Thursday in the US journal Science, helped clarify when canine transmissible venereal tumor (CTVT), one of two known transmissible cancers, first arose in dogs.

The researchers estimated that CTVT first appeared in a single dog that lived about 11,000 years ago, a point by which dogs were domesticated. The cancer survived after the death of this dog by the transfer of its cancer cells to other dogs during mating.

The researchers sequenced the genomes of CTVTs from two modern canines, an Australian Aboriginal camp dog and an American cocker spaniel from Brazil, and found that the two tumors shared almost 2 million somatic mutations, over a hundred times more somatic mutations than found in most human tumors.

What's important is that CTVT has remained stable, continuing to plague domestic dog populations for thousands of years, they noted.

"The genome of this remarkable long-lived cancer has demonstrated that, given the right conditions, cancers can continue to survive for more than 10,000 years despite the accumulation of millions of mutations," Elizabeth Murchison, first author from the Wellcome Trust Sanger Institute and the University of Cambridge, said in a statement.

Analysis of these genetic variants revealed that the individual dog that first gave rise to the cancer 11,000 years ago may have resembled an Alaskan Malamute or Husky. It probably had a short, straight coat that was colored either grey-brown or black.

Its genetic sequence could not determine if this dog was a male or a female, but did indicate that it was a relatively inbred individual.

"We do not know why this particular individual gave rise to a transmissible cancer," Murchison said. "But it is fascinating to look back in time and reconstruct the identity of this ancient dog whose genome is still alive today in the cells of the cancer that it spawned."

Murchison said that the patterns of genetic variants in tumors from different continents suggested that the cancer existed in one isolated population of dogs for most of its history.

"It spread around the world within the last 500 years, possibly carried by dogs accompanying seafarers on their global explorations during the dawn of the age of exploration," Murchison said.

Transmissible cancers are extremely rare in nature. Cancers, in humans and animals, arise when a single cell in the body acquires mutations that cause it to produce more copies of itself. Cancer cells often spread to different parts of the body in a process known as metastasis. However, it is very rare for cancer cells to leave the bodies of their original hosts and to spread to other individuals.

Apart from the dog transmissible cancer, the only other known naturally occurring transmissible cancer is an aggressive transmissible facial cancer in Tasmanian devils that is spread by biting.

Posted in: Biology

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