The Lazarus Project team says they have been able to recover cell nuclei of the extinct gastric-brooding frog, Rheobatrachus silus,
from tissues collected in the 1970s and kept for 40 years in a conventional deep freezer. 

The genome of
Rheobatrachus silus, extinct since 1983, has been revived and reactivated by a team of scientists using
somatic cell nuclear transfer
to implant a "dead" cell nucleus into a fresh egg from another frog species.
 

Rheobatrachus silus is famous for swallowing its eggs, brooded its young in its stomach and giving birth through its mouth. The "de-extinction" project aims to bring the frog back to life.
 

In repeated experiments over five years, the researchers used somatic cell nuclear transfer (SCNT), which is banned by the Obama administration in the United States. They took fresh donor eggs from the distantly related Great Barred Frog, Mixophyes fasciolatus, inactivated the egg nuclei and replaced them with dead nuclei from the extinct frog.

Some of the eggs spontaneously began to divide and grow to early embryo stage – a tiny ball of many living cells.

Although none of the embryos survived beyond a few days, genetic tests confirmed that the dividing cells contain the genetic material from the extinct frog.

A gastric-brooding frog, Rheobatrachus silus, giving oral birth in the lab of Mike Tyler of the University of Adelaide. Photo: Mike Tyler, University of Adelaide

"We are watching Lazarus arise from the dead, step by exciting step," says the leader of the Lazarus Project team, Professor Mike Archer, of the University of New South Wales, in Sydney. "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."

The technical work was led by Dr Andrew French and Dr Jitong Guo, formerly of Monash University, in a University of Newcastle laboratory led by frog expert, Professor Michael Mahony, along with Mr Simon Clulow and Dr John Clulow. The frozen specimens were preserved and provided by Professor Mike Tyler, of the University of Adelaide, who extensively studied both species of gastric-brooding frog – R. silus and R. vitellinus - before they vanished in the wild in 1979 and 1985 respectively.

 A whole frozen gastric-brooding frog after 40 years in a conventional freezer. Photo: Bob Beale

UNSW's Professor Archer spoke publicly for the first time today about the Lazarus Project and also about his ongoing interest in cloning the extinct Australian thylacine, or Tasmanian tiger, at the TEDx DeExtinction event in Washington DC, hosted by Revive and Restore and the National Geographic Society.

Researchers from around the world are gathered there to discuss progress and plans to 'de-extinct' other extinct animals and plants. Possible candidate species include the woolly mammoth, dodo, Cuban red macaw and New Zealand's giant moa.

The results are yet to be published.