Tasmanian Devil DNA shows signs of cancer fightback
FIGHTING CANCER WITH EVOLUTION: The Tasmanian devil
A genetic study of Tasmanian devils has uncovered signs that the animals are rapidly evolving to defend themselves against an infectious face cancer.
One of just three known transmissible cancers, this tumor has wiped out 80% of wild devils in the past 20 years.
Researchers looked at samples from 294 animals, in three different areas, before and after the disease arrived. Two small sections of the devil genome appear to be changing very fast – and contain likely cancer-fighting genes.
The team, made up of US, UK and Australian scientists, described their findings in the journal Nature Communications. They say the results offer much-needed hope that the species, which is unique to Tasmania, could survive the disease.
Devil facial tumor disease (DFTD) was discovered in 1996 and kills nearly every devil it infects. Essentially a single tumor that jumps between hosts, it is transferred when the aggressive beasts bite each other’s snouts.
Only two other infectious cancers are known to science. A similar tumor is shared between the genitals of dogs when they mate, and has traversed the globe since it originated 11,000 years ago; another was discovered in 2015 affecting clams on the US west coast.
Speaking to journalists in a teleconference, co-author Dr Paul Hohenlohe said he and his colleagues were in a unique position to observe the Tasmanian devil population responding to the cancer threat – because their samples spanned separate locations and reached from 1999 through to 2014.
Using the latest DNA sequencing methods, they were able to look for changes right across the devil genome.
“We characterized about 800,000 locations across the genome of each individual Tasmanian devil,” said Dr Hohenlohe, an evolutionary biologist at the University of Idaho.
“Our goal is to look for genetic variants that could convey some sort of resistance… so that it may be possible to manage captive populations to ensure that that genetic variation is maintained.”
A wealth of data
Sure enough, among that wealth of data, the team found that two particular stretches of DNA were under acute selection pressure: they were changing faster than the rest of the genome, and specific gene variations were obviously on the rise – in all three populations.
Most importantly there were seven particular genes, within those favored regions, that looked like good anti-cancer candidates. They were connected to the activity of the immune system, for example, or there was a matching gene in humans with a known link to cancer.
“Particularly, there are several that seem to be involved in directing immune cells to dysfunctional cells or pathogens, and we think those are particularly promising,” said Dr Brendan Epstein from Washington State University, the paper’s first author.
His colleague Dr Andrew Storfer, also from Washington State, said this was cause for optimism. Despite the devils’ steep decline, several populations – including those in the study – have survived beyond the point where scientists expected them to vanish.
These findings may explain why.
“First and foremost, this gives us hope for the survival of the Tasmanian devil, which is predicted to be extinct but isn’t,” Dr Storfer said. “We see that the devils apparently are evolving genes that may be associated with resistance to the disease.”
Particularly exciting, he said, was the speed at which these adaptations appeared to be happening.
“We’re talking about roughly six generations in some populations, which is a very short period of evolutionary time.”
“The team is now working to characterize the specific genes in more detail. There may be things to learn that could help tackle cancer in humans.” –Dr Andrew Storfer
“One of the big questions is, what do these cancers have in common? [Then] we can figure out how cancers evolved to be transmissible in the first place,” Dr Storfer said.
The tumor spreading between bivalves in the Pacific can actually jump from one species to another, he added.
“The fear is that we may see more cancers down the road that are transmissible between species.”
Dr David Rollinson is a biologist at the Natural History Museum in London who specializes in the genetics of how hosts and parasites evolve together. He said the new study was an impressive – and encouraging – example of natural selection in action.
“I find it quite exciting,” Dr Rollinson goes on to say. “There’s been great concern that the Tasmanian devils may be wiped out by this strange, transmissible cancer.
“And it now seems that there’s just a little bit of hope – that the selection pressure is actually driving a response by the devils, so they’re getting a genetic profile that might actually give them some protection.”
Tasmanian devil milk fights superbugs
Milk from Tasmanian devils could offer up a useful weapon against antibiotic-resistant superbugs, according to Australian researchers.
The marsupial’s milk contains important peptides that appear to be able to kill hard-to-treat infections, including MRSA, say the Sydney University team.
Experts believe devils evolved this cocktail to help their young grow stronger and scientists are looking to make new treatments that mimic the peptides.
They have scanned the devil’s genetic code to find and recreate the infection-fighting compounds, called cathelicidins.
PhD student Emma Peel, who worked on the research which is published in the Nature journal Scientific Reports, said they had found six important peptides.
These appear to be similar to peptides in the milk of other marsupials, which means these animals are worth studying too.
“Tammar wallabies have eight of these peptides and opossums have 12,” she said, adding that studies into koala’s milk had now started.
Experts believe marsupials are good to study because their babies have to thrive in a relatively dirty environment.
Tasmanian devil mothers give birth after only a few weeks of pregnancy. The tiny offspring then spend the next four months maturing in their mother’s pouch.
The Sydney team recreated the six devil peptides that they found and tested them on 25 types of bacteria and six types of fungi.
One of the synthetic peptides – Saha-CATH5 – appeared to be particularly effective at killing the superbug methicillin-resistant Staphylococcus aureus or MRSA.
Many people carry MRSA on their skin and inside the nose and throat. Most of the time, the infection is harmless.
But if it enters the body through an open wound for example, it may cause problems, which is why people staying in hospital are at a higher risk.
MRSA is treatable, but only with a combination of antibiotics that can get round the resistance problem.
It also appeared to kill another resistant bug, called Vancomycin-resistant enterococcus, as well as fungi, called Candida, which are commonly involved in skin infections.
Experts agree that we urgently need new drugs to fight treatment-resistant infections. A recent review warned that by 2050, superbugs could kill one person every three seconds around the world unless urgent action was taken.
Dr Richard Stabler, Associate Professor in Molecular Bacteriology at the London School of Hygiene & Tropical Medicine, said: “We need to do this hunting in unusual places for new antibiotics. People are beginning to explore and find new molecules.”