Back from the dead
One day we may again hear the roar of a woolly mammoth as it is brought down by a group of Neanderthal hunters, as scientists race to resurrect long dead animals with modern cloning technology. Jacqui Hayes reports.
It may seem like science fiction, but it’s not. Not even ten years after the first mammal was cloned, scientists are racing to clone the first extinct species.
February 2007 marks 10 years since Scottish scientists announced they had successfully cloned Dolly the sheep. It was a huge accomplishment, and the culmination of decades of research. Now she sits at the top of a long list of clones including cats, pigs, cows, a dog, monkeys, horses and goats.
Perhaps, though, the most significant addition to this ever-growing list was Noah the gaur. The gaur is an endangered, large, dark-coloured ox with a humplike ridge on its back and white or yellow stockings on all four legs – and its numbers are steadily declining.
Noah became the first member of an endangered species to be successfully cloned when he was born in 2001. He was brought to term by a surrogate mother – Bessie, a domestic cow. Unfortunately, Noah died after only two days due to an infection reportedly unrelated to cloning.
The U.S. biotechnology company that cloned Noah, Advanced Cell Technologies (ACT), proclaimed their work as altruistic. “We don’t see this as a profit centre for the company,” according to Michael West, President of ACT. “Our thought is simply that the human species has casually used technology to despoil the planet, the least we can do is use the technologies we work with every day to make a small contribution to save innocent and endangered species.”
Born along with Noah was an intriguing new method of maintaining biodiversity. Approximately 100 species continue to go extinct each day, and governments and conservation groups are fighting to protect the animals endemic to their lands.
The San Diego Zoo, in the U.S., hosts a frozen repository of tissue from 675 endangered species. Twenty-five years ago the Frozen Zoo was filled only with sperm and ovaries. Now it also holds cell-lines and tissue samples from any part of the body.
Using skin cells from the Frozen Zoo, ACT cloned another endangered species in 2003. Two bantengs – another Southeast Asian ox – were created using the same basic method as for Dolly the sheep. The company took DNA from banteng skin cells and put it in the egg of a domestic cow that had already had its DNA removed. What was unique with the banteng was that a member of a different species provided the egg.
Nature has its own frozen zoo. Unlike the youthful San Diego Zoo, in existence for only 25 years, the vast wastelands of Siberia have held animals trapped in permafrost for as long as 200,000 years. This repository hasn’t escaped the attention of ambitious scientists.
In 2002 Akira Iritani, from Kinki University in Japan, announced plans for his team to create ‘Pleistocene Park’ – a home for resurrected woolly mammoths, extinct for approximately 3,500 years. Later additions would include the woolly rhinoceros, which hasn’t roamed the Earth for more than 10,000 years.
It is a race against time, partly because climate change is melting the permafrost in Siberia, uncovering ancient animal remains at an increasing rate. Once uncovered, the specimens begin to rot, degrading DNA that may have remained intact for eons.
Other extinct animals on cloning experts’ to-do list include the Tasmanian tiger and the Spanish mountain goat, both of which were driven extinct by human forces.
Freezing preserves biological molecules that would otherwise swiftly degrade after death. A dead cell doesn’t possess any of the usual machinery required to repair DNA damage, and long chains of DNA disintegrate into smaller fragments while some bases (A, T, C, and G – the molecules that make up the genetic code) mutate into others.
Cells with DNA in fragments only 100 to 200 base pairs long cannot be used for cloning as they are not able to grow, divide and create proteins in the same way as cells with intact DNA. However, if an animal is frozen within days of dying – and remains frozen – the process of degradation is slowed or even halted.
Iritani hoped, at first, to find frozen sperm from a mammoth. The sperm would be used to impregnate a modern-day elephant, creating a hybrid species. As more mammoths are born the elephant genes could eventually be bred out. Frozen sperm, though, would be an incredibly lucky find. As an insurance policy, any tissue samples found are stored, as the team firmly believes that scientists will find a way to piece together the fragmented DNA.
Creating a real-life Pleistocene Park may sound like a rather far-fetched idea, but it is already under way. A Russian scientist has been cultivating a suitable location in Siberia for more than a decade. He hopes to recreate the entire landscape and ecosystem of 10,000 years ago – perfect for recently resurrected woolly mammoths. In total, the park would be about twice the twice of England.
While mammoth experts scoff at such an idea, Iritani has already proven he knows what he is doing. Six months before announcing plans for Pleistocene Park, Iritani’s team successfully transplanted a spinach gene into a pig. The result was an animal that creates less fatty acid and produces a healthier pork product. Only time will tell if he can be successful in his new, and far more ambitious project.
The woolly mammoth is a popular target among many cloning experts. The disgraced South Korean scientist Hwang Woo-Suk (see Cosmos, Issue 8, p64), who successfully cloned Snuppy the dog, had obtained woolly mammoth tissue for cloning purposes. In another admission of breached ethics, Hwang recently admitted in court that his team obtained the samples by paying the Russian Mafia.
Other extinct animals on cloning experts’ to-do list include the Tasmanian tiger and the Spanish mountain goat, both of which were driven extinct by human forces. It is even conceivable that animals as long-gone as dinosaurs will one day make the list, despite not being preserved immediately after death.
Most twentieth century scientists insist that Jurassic Park is still science fiction, while others readily admit the methods described in the movie thriller could actually be one future possibility. In Jurassic Park, dinosaur DNA was obtained from the blood in the stomachs of insects entombed in amber. The sequences vital for making the right dinosaur were targeted and spliced into host DNA from modern amphibians, and the dinosaurs were grown in artificial eggs.
The struggle to recover ancient DNA has had a tumultuous history in life, as well as in the movies. Because DNA degrades over time, it was long considered impossible to retrieve anything useful. False reports in 1994 of a DNA find in an 80-million-year-old dinosaur bone was only the first in a series of high-profile failures as researches tried to obtain DNA of ancient animals.
The naysayers were finally proved wrong only last month. DNA from our closest ancestors, the Neanderthals, was not only discovered uncontaminated, but was also successfully sequenced.
Discovering 80-million-year-old DNA might be a stretch, but 38,000-year-old DNA is achievable. Edward Rubin, from the Lawrence Berkeley National Laboratory in California, developed a method of targeting specific sequences in DNA. His team sequenced a total of 65,000 base pairs, recovering 29 of the 35 genes they targeted. Scientists expect the entire genome to be sequenced within two years.
The technologies that made it possible are very recent developments. While reflecting on the new developments in DNA sequencing, Rubin commented that “we’re poised to see technological advances that will enable us to do things tomorrow that today don’t seem so feasible.”
While some scientists work towards reconstructing ancient DNA, others are focusing on the unique problems that arise when a surrogate mother from a closely related species is used during the cloning process.
A cloned animal receives the DNA from the nucleus of a normal body cell, which codes for the development of most structures and processes in the body. But mammalian cells contain two distinct genomes: one in the nucleus, and another genome that exists only in the cell’s powerhouse, the mitochondria.
These minature organs, once free-living bacteria before they were ‘ingested’ by other early cells, are the component of a cell that converts sugars into ATP – the universal energy currency of the body. Mitochondrial DNA codes for about 13 proteins necessary for ATP production.
In mammals, the mitochondrial DNA is passed from mother to offspring without any changes, except for random mutations. The mitochondrial DNA in sperm is destroyed by the egg during fertilisation.
“Now is the time … to ask how much of our limited resources should be devoted to seeking biotechnology-based solutions to conservation problems.”
A recent study set out to determine whether the same process would occur when a macaque (a type of monkey) embryo was created using an egg from a rabbit. Surprisingly, the mitochondrial DNA from both species survived as the embryo began to develop into a macaque.
Debates in the scientific community continue as studies like these raise questions about hereditary. Are clones with a mother from a different species a true copy? Does it matter? What about the natural bacteria in the gut, passed from mother to offspring? How would a monkey, whose mother was a rabbit or a baboon, fare outside a zoo?
If a jury existed for these matters, it would still be out. While other areas of science and society have had hundreds of years to develop sophisticated philosophical arguments, genetic engineering uncovers novel ethical issues on a seemingly daily basis.
As scientists question the ethics of creating and resurrecting animals, animal activists also worry that cloning may replace large-scale conservation. “Now is the time … to ask how much of our limited resources should be devoted to seeking biotechnology-based solutions to conservation problems,” wrote David Ehrenfeld of Rutgers University in the U.S., in an essay on vertebrate cloning published earlier this year in the U.S. journal Conservation Biology.
Ehrenfeld considers cloning a glamorous technology with the potential to create a false impression of an easy, high-tech solution to the ongoing problem of extinction. It is also an expensive process, likely to be biased toward cloning animals that would become zoo or theme park attractions. “The cloning of endangered rays, caecilians [snake-like amphibians] or vipers may have to wait until we have done the showier rare birds and animals,” according to Ehrenfeld.
While one argument says it is appropriate – even necessary – to bring back unique animals that humans have driven to extinction, other arguments which are equally valid maintain that it is unethical to ‘play god’ by resurrecting two of every kind. This may be one situation where the limits of science are, perhaps, less of an issue than the limits of our own ethics.