THE LONG-CHERISHED dream of cloning much-loved family pets came a step closer last week, when it was announced that American scientists have succeeded in cloning a domestic cat for the first time. The two-month-old tortoiseshell kitten, called Cc - short for carbon copy - appears to be healthy, writes Nick Mays.
Cats are the sixth mammal - after sheep, cows, mice, goats and pigs - to be cloned with the nuclear transfer technique used to produce Dolly the sheep.
However, as with all the previously cloned species, the cloning success rate is low. Cc was the only live birth out of 87 cloned embryos implanted into surrogate mothers.
Although Cc is a genetically identical twin of the donor cat, it is far from a carbon copy. The pattern on cats coats is only partly determined by genes; it also depends on the environment in the womb as the kitten embryo grows. Ccs colouring is unique.
Cats personalities, as with those of any cloned animal, are also likely to be heavily influenced by conditions inside the womb and during their first few months, making an exact replica of the original animal still something confined to the realms of science fiction.
The female kitten was created by Dr Mark Westhusin and colleagues at Texas A&M University in College Station, home of the much-vaunted Missyplicity Project which has been trying, for the past five years, to create a cloned dog.
The first-ever cloned cat, shown here at seven weeks old,
with Allie, her surrogate mother.
team took DNA from an adult female tortoiseshell cat named
Rainbow and injected it into a hollowed-out egg
cell whose nucleus had been removed.
The egg was then kick-started into life with an electric shock and implanted into a surrogate tabby mother.
The experiment, reported in the journal Nature, was paid for by John Sperling, an 81-year-old financier who owns a company called Genetic Savings & Clone. Mr Sperling says he aims to offer the technology to wealthy people seeking to clone their favourite pet animals, and wants to charge pet owners to clone their animals.
Cloned cats are expected to attract a price tag of around £7,000, although the price is expected to fall to around £700. Cloned dogs will be much more expensive, with £70,000 being the initial price, possibly dropping to a mere snip at £5,000.
Despite the hype, however, the success rate will have to be improved if pet cloning is to be a reality and highlights once again the dangers of cloning. Cloned animals also tend to be larger than normal and have been shown to suffer from immune system problems.
Tests have shown that cloned animals have shorter than normal lifespans and are unusually vulnerable to disease, according to research published in January. Scientists in Tokyo have shown that cloned mice die significantly earlier than mice conceived naturally. They also have weakened immune systems and suffer from pneumonia, tumours and liver failure.
The new mouse research was led by Dr Atsuo Ogura at the National Institute of Infectious Diseases in Tokyo. It examined 12 mice cloned from testes cells. The cloned mice began to die after 311 days, with 10 dying before 800 days. Out of a control group of seven mice that were conceived naturally, only one died before 800 days.
When the scientists examined six of the dead clones all had severe pneumonia, two had cancer and four had liver failure, they report in Nature Genetics. Their immune systems were also weak. The clones were created in the same way as Dolly. A cell nucleus and its DNA were removed from a donor cell and placed inside an unfertilised egg, from which its nucleus had been removed.
It was disclosed a few weeks ago that Dolly the sheep, the first mammal to be cloned from an adult, had arthritis in one leg, a possible symptom of premature ageing. Dolly was the only healthy live-born lamb out of 277 attempts at the Roslin Institute, Edinburgh. Earlier this year, Prof Ian Wilmut, one of the scientists who cloned Dolly, called for a full inquiry into the health of all cloned animals.
1999 researchers found evidence that she may be ageing prematurely.
Scientists at PPL Therapeutics, the company that worked with
the Roslin Institute to create Dolly, looked at structures
in her cells called telomeres. Made from protein and nucleic
acid, these cap the ends of chromosomes, protecting them from
Telomeres have been linked to the natural life cycle of cells. Each time a cell divides, the telomeres become shorter until, after a predetermined number of divisions, they crumble away, allowing the cell to die. Dollys telomeres appear to be shorter than normal, suggesting that she may be genetically older than chronological age.
Despite the ongoing concerns over the drawbacks of cloning, the scientists at Texas A & M remain upbeat about Ccs successful birth and the possibility of cloned pets at last becoming a reality for pet lovers worldwide.
A kitten was delivered by caesarean section on Dec 22, 2001, 66 days after the embryo was transferred, said a team spokesperson. The kitten was vigorous at birth and appears to be completely normal.
Tests carried out after Ccs birth confirmed that the kitten was a clone - genetically identical to the donor.