Tasmanian clues emerge
The facial cancers that are devastating populations of Tasmanian devils in Australia are a nerve tumor that escaped its original host and became a parasite of the cultural icon, passing from one devil to the next by bites when the animals are fighting or mating, researchers reported Thursday.
A genetic analysis of tumors from Tasmanian devils widely separated geographically shows that all the tumors are virtually identical and distinct from the animals’ own genomes, researchers in the United States and Australia reported in the journal Science. The tumors probably arose from Schwann cells, which normally play a role in protecting and cushioning nerves.
The analysis provides clues to a way to diagnose the disease early and represents a major step toward the development of a vaccine that could protect the remaining animals in the wild, said biologist Elizabeth P. Murchison of the Cold Spring Harbor Laboratory in Cold Spring Harbor, N.Y., and the Australian National University in Canberra, lead author of the paper.
Tasmania is the only natural habitat of the fox-sized creatures, the world’s largest marsupial carnivore. The animals release a foul odor under stress, and they screech and scream when they feed, a behavior that led to their name. Their powerful jaws enable them to eat entire cows, including bones and fur.
But beginning more than a decade ago, biologists noticed the appearance of the facial tumors, a condition now known as devil facial tumor disease. Confined primarily to the face and jaw, the tumors prevent the animals from eating, and they can also attack internal organs. The disease, which is invariably fatal, is one of only two types of cancers in animals that are transferred from animal to animal by tumor cells. The other occurs in dogs.
The population of devils in the wild has already dropped by 60%, and experts predict that unless something is done, the tumors could force the animals into extinction in 20 to 25 years. One possibility under consideration is the construction of 3-foot-high fences across broad parts of Tasmania that would keep infected animals isolated from healthy ones.
Analyzing the genetic code of the tumors as well as the complete set of genes that are turned on or off in a cancer cell, the researchers concluded that the tumors probably arose in a Schwann cell in a single Tasmanian devil, then began spreading through the population. How and where the first tumor developed, however, is still a mystery, but the team hopes the genetic analysis may provide some insight.
The researchers also found a protein called periaxin in the tumors. This protein, which is normally found in Schwann cells, could be a marker for early stages of the disease when it’s present in the animals in high levels, they speculated.
Meanwhile, they are looking for genes that might influence the pathology and transmission of the tumor in the hope that they might provide a good lead on a vaccine.