Researcher puts the case for cloning in wake of sheep death

The death of Australia's first cloned sheep, Matilda, is not the only setback in efforts to clone livestock species -- nor will it be the last, says Dr Ian Lewis, program leader with the Cooperative Research Centre for Innovative Dairy Products.

The CRC has also lost cloned animals -- of 14 cloned Holstein Friesian dairy calves carrying an extra copy of a gene for the milk protein casein, only two remain alive. Seven died soon after being born, apparently because of placental and other problems.

Australia's first cloned dairy cow, Suzi, born in 2000, shortly before Matilda the sheep, is still alive and healthy, but her sister clone, Mayzi, died last year of acute mastitis -- an udder infection, probably unrelated to any underlying genetic problem. Both cows gave birth to normal, healthy calves through artificial insemination.

Lewis says the CRC's experience reflects the fact that, with any new technology, a high rate of error or failure is likely in the early stages of development: "It's only six years since Dolly was born, and many people thought at the time that it wasn't possible to clone large mammals.

"In the early days, we were lucky if only a few embryos survived, but now we have hundreds of apparently healthy mammals, including sheep, cattle and goats. It doesn't always misfire. Increasingly, it works in a large number of cases -- it turns out to be easier to clone some species, such as cattle and goats, than others such as sheep and mice."

Lewis says molecular geneticists are learning very rapidly about problems that can affect cloned animals, which arise when certain genes are inappropriately switched on or off in the original, somatic cell line, resulting in developmental problems in the embryo, or later in the animal's life.

Despite failures, it is clear that, after the cloned generation, any imprinting errors in the genetic programs controlling embryonic development and subsequent growth are removed.

"All the offspring of cloned animals are normal and healthy, even if both parents have been cloned by nuclear transfer," Lewis says. "After one germline cycle, any epigenetic problems disappear.

"There are more than 30,000 genes in a cell, and at any time, only 15 per cent of them are active in specific tissues. You're trying to switch them all back on, then reset them in the correct manner for normal embryonic development. If mistakes occur, there will be bad outcomes.

"We've had cloned animals with fibrotic livers, polycystic kidneys, osteoporosis, and muscular problems later in life. We have a team of veterinarians and pathologists trying to pinpoint the problems, and trying to work out which genes are not reprogramming properly.

"High-throughput assays of gene activity are going to give us the information we need -- if the activity profiles aren't right, we will simply discard the embryo. Certain cell lines appear to be better for cloning than others -- our high-casein calves, for example, were produced from skin fibroblast cells."

Producing the right brew

The problem seems to lie in incompatibilities between gene-expression profiles in the nuclei of some somatic cell lines, and the biochemical environment of the recipient, evacuated oocyte.

"We're starting to work out what cytoplasmic factors in the oocyte are involved in reprogramming the genes for normal embryonic development," Lewis says. "Once we know what they are, we can just add them to cell lines to produce the right brew."

The potential benefits from cloning transgenic livestock are enormous, he says: "We will be able to produce vaccines in milk, produce vital medicines more cheaply, produce better milk and meat more efficiently.

"Australia's dairy farmers are already the most efficient in the world, and our dairy exports are worth $AUD3 billion a year. But if we don't have access to these technologies, we will inevitably fall behind.

"There are some really exciting possibilities for the northern beef herd. You can't use artificial insemination in the tropics, because of logistical problems -- the stocking rate in the tropics is only around one animal per square kilometre."

Productivity could be rapidly improved by cloning an elite bull and allowing its clones to find receptive cows in their own time.

Lewis says there seems to be a paradigm that all reproductive technologies are bad, but if everyone took such a view, many scientific advances of enormous benefit would never have occurred.

"Cloning is still very new. We shouldn't expect it to work perfectly, right away. We should look at the big picture, and ask, 'At the end of the day, is it worth it?'

"Yes, it is. When Lindbergh flew across the Atlantic 80 years go, people would not have believed that today, at any one time, more than 70,000 people would be in the air, in huge passenger jets. If Florey and Alexander had given up on penicillin in the early stages, how many millions of lives would not have been saved?"