Scientists at the University of South Wales have succeeded in growing early stage cloned embryos containing the DNA of the extinct gastric-brooding frog. The achievement is the crucial first step in the attempt to bring the species back from extinction.
The Project Lazarus team led by Professor Mike Archer used cloning methods to insert preserved genetic material of the extinct gastric-brooding frog into the donor eggs of another species of extant Australian marsh frogs and were able to grow the eggs into early stage embryos known as a blastula consisting of hundreds of cells.
Project Lazarus is a breakthrough because it demonstrates for the first time that it is possible using laboratory techniques to bring back species from extinction. The Sydney Morning Herald reports that one of the project scientists, conservation biologist Michael Mahony, said: "This is the first time this technique has been achieved for an extinct species."
The Sydney Morning Herald reports Archer said: "In the beginning, the single cell eggs just sat there. But then, all of a sudden, one of the cells divided, and then it divided again, and again. There were a lot of high fives around the laboratory at that point."
National Geographic reports that gastric-brooding frogs, as the name implies, exhibit an unusual form of reproductive behavior in which the female swallows her fertilized eggs. Popular Science explains that the fertilized eggs are coated in prostaglandin which causes the frog's stomach to stop producing acidic digestive juices and transforms it into a "makeshift womb" where the young develop. When the froglets are fully developed the female simply regurgitates them.
There are two species of gastric-brooding frog native to the creeks in a small area of the tropical forest in Queensland, Australia, National Geographic reports. The species are Rheobatrachus silus and the northern gastric-brooding frog Rheobatrachus vitellinus.
Biologists discovered the two species in 1973 and 1984 respectively, but by the middle of the 1980s the species had gone extinct before scientists had the opportunity to study their biology in detail.
According to the researchers the species became extinct due to a combination of factors including habitat degradation, pollution and disease such as the chytrid fungus.
Biologists hope that understanding how the frog can stop its stomach from producing digestive juices may lead to useful medical applications for people with gastric illnesses.
Mike Archer, paleontologist at the University of New South Wales, speaking at Friday's TEDx Conference on DeExtinction at the National Geographic headquarters in Washington D.C., said: "This was not just any frog. No animal, let alone a frog, has been known to do this – change one organ in the body into another... I think we're gonna have this frog hopping glad to be back in the world again."
The team obtained the genetic material from gastric-brooding frog tissues collected in the 1970s and preserved for 40 years in a deep freezer. Professor Archer and his colleagues implanted "dead" cell nucleus from a frozen specimen of the gastric-brooding frog into a fresh egg of the living Great Barred Frog.
In experiments conducted over five years, the research team used a laboratory technique known as somatic cell nuclear transfer which involved taking fresh donor eggs from a distantly related species the Great Barred Frog, Mixophyes fasciolatus, inactivating the egg nuclei and then replacing them with dead nuclei from the extinct gastric-brooding frog. According to the team, some of the eggs were able to divide and grow spontaneously to early embryo stage blastulas consisting of many living cells.
According to the researchers, although the embryos survived for only a few days, tests confirmed that the dividing cells contained genetic material from the extinct frog.
The scientists say they are uncertain why the embryos survived for only a few days, but Archer said it was probably due to the manner of handling.
Archer told the audience at the TEDx Conference: "We are watching Lazarus arise from the dead, step by exciting step. We’ve reactivated dead cells into living ones and revived the extinct frog’s genome in the process. Now we have fresh cryo-preserved cells of the extinct frog to use in future cloning experiments. We’re increasingly confident that the hurdles ahead are technological and not biological and that we will succeed. Importantly, we’ve demonstrated already the great promise this technology has as a conservation tool when hundreds of the world’s amphibian species are in catastrophic decline.”
Professor Michael Mahony led the technical work carried out in a University of Newcastle laboratory. The team included Dr Andrew French and Dr Jitong Guo, formerly of Monash University, and Mr Simon Clulow and Dr John Clulow.
The frozen specimen used were preserved and provided by Professor Mike Tyler of the University of Adelaide who had the opportunity to study the species before they became extinct.
Professor Archer also spoke at the TEDx Conference about his interest in cloning the extinct Australian thylacine, or Tasmanian tiger.
Researchers from around the world present at the DeExtinction conference identified other possible "de-extinction" candidates including the woolly mammoth, dodo, Cuban red macaw and New Zealand’s giant moa.
The TEDx DeExtinction event in Washington DC, was hosted on March 15 by Revive and Restore and the National Geographic Society.