Great leap forward: cloningthe Gastric Brooding Frog

The Gastric Brooding Frog giving birth. Photo: Department of the Environment.

 

BY JACK CORBETT

 
Cloning an extinct species has long been a staple of science fiction, but is it about to become a reality?

When Jay Savage first discovered the golden toad in 1966, the species became a poster specimen for the biodiversity of Costa Rica. While it lived in a small area, roughly 10 square kilometres within the Monteverde Cloud Forest Reserve, the toad was abundant; over the course of 17 years, nearly 1500 individuals were counted every year throughout their limited range. Then, in 1988, only 10 toads were found. The next year only a single male was located and after that the species promptly vanished, finally being declared extinct in 2004.
 


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Environmentalists have noted a swift decline in amphibian populations worldwide over the past few decades, of which the Costa Rican golden toad is only one of many. A combination of climate change, habitat destruction and the spread of the fungus Batrachochytrium dendrobatidis are believed to have contributed to this, and as a result the background extinction rate – which has remained relatively constant through history – is nearly two hundred times what it should be.

One of the most notable victims of this extinction is the gastric-brooding frog, an Australian species which disappeared a decade after its discovery in 1981. The frog was named after the way it hatched its young: shortly after mating and spawning the female would swallow the eggs and brood them inside her stomach, the baby frogs being expelled once they had grown. The frog represented a completely unique family, as no others in Australia have been observed to hold this ability.

The gastric-brooding frog had barely been discovered when it was driven to extinction, which is believed to have been caused by the destruction of its habitat. Like the golden toad it was confined to a small area of forest in southern Queensland, and even slight changes to its environment could have had a disastrous effect on the population. A few years after it disappeared a subspecies was discovered but, within a year, it too had died out. Since then the frog has been frequently cited as a victim of human interference, though not to the same extent as the Thylacine.

Thanks to a recent breakthrough, though, this may no longer be the case.

In March, a group of researchers from the University of New South Wales announced they had cloned embryos of the gastric-brooding frog as a part of the Lazarus Project. The project, headed by Dr Mike Archer, also responsible for heading a project based around cloning the Thylacine, is one of several de-extinction projects across the world, and is the first to have made such a major leap forward in creating a living embryo.

The embryos were created using somatic-cell nuclear transplantation, or SCNT, the same process used to create Dolly the sheep. In this process, the nucleus of a living cell is removed and transplanted into an egg cell which has had its own nucleus inactivated. Just like Dolly, the Lazarus Project represents a major step forward for cloning, but with the gastric-brooding frog an entirely new set of hurdles have presented themselves. The chief challenge for the project is that there are no living gastric-brooding frogs to use as egg donors; the closest that can be used is a distant relative, the barred frog.

‘The challenge for the Lazarus Project is that the frog we’ve been using as a host species – the one which we got the eggs for SCNT – only breeds pretty much once a year. So we only had, really, one go a year for about a week in which to do these trials,’ said Dr Archer. ‘In all the SCNT projects we’ve been involved in related to the Lazarus Project, it’s always the nucleus that’s being moved is a different species than the egg into which we’re putting it. So it’s a sort of cross-species cloning, which is a very important distinction between what happened with Dolly and what we’re doing.’

Dr Archer also mentioned the impact that Jurassic Park, both the film and the original novel by Michael Crichton, have had in bringing attention to de-extinction. ‘Michael Crichton, in his introduction to the book Jurassic Park… he’s quite honest that he wrote this book to scare people to death about ever thinking about [cloning]. He’s gone, but you have to say “what a colossal failure”, if that was his purpose. All he’s done is excited the next generation of people to think about the possibility.’

Despite the initial success with the embryos, they didn’t survive past a few days, failing to move past the gastrulation stage of development. There was fear that the DNA being used was of poor quality, but tests with fresh DNA halted at the same stage of development. Despite this setback the Lazarus Project’s team remains optimistic, and are possibly even more excited now than they were at the start of the project.

‘We haven’t got a tadpole, and we haven’t got a frog,’ explained Dr Archer. ‘So we’re a long way from the finishing line, but we’re a lot further in the race than we thought we’d be.’
 

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