Dolly, You're History

By MICHAEL D. LEMONICK

In the year and a half since Scottish embryologist Ian Wilmut presented Dolly, the cloned sheep, to an astonished world, ethicists and policymakers have been struggling with the unsettling implications of his research. Could scientists use Wilmut's method to clone not just sheep but also billionaires, basketball players and bodies grown for spare parts? Should medical entrepreneurs be allowed to pursue cloning wherever it leads? Or should the government step in now and outlaw it before it starts?

For reproductive biologists, these issues pale in the face of two more immediate and practical questions: Is Dolly really a clone--and if so, can anybody make one? It's taken a while, but the answers are finally in. The verdict, according to a trio of reports in the current issue of Nature: yes and yes. Not only have Dolly's pedigree and her immaculate conception been established beyond all reasonable doubt, but she has been joined by litter upon litter of perfectly cloned mice. Cloning has, with a speed no one anticipated, been transformed from an astonishing technical tour de force into what seems almost a mundane laboratory procedure.

What makes Dolly and these new mice special--and distinguishes them from barnyards of previously cloned pigs, cows and sheep--is that they were cloned from adult cells or, as the scientists call them, differentiated cells. All those earlier clones were made from fetal cells, which have no specialized function but carry the potential to turn into anything and everything the body needs.

Differentiated cells, by contrast, have already become specialized, with some genes turned on and some turned off, making them into breast or liver or pancreas cells. Although a differentiated cell still contains all the genetic information needed to create a whole new creature, much of that information is suppressed. Nobody had ever succeeded in reprogramming its genes back to the comparatively undifferentiated state suitable for cloning.

Until Dolly, that is. What Dolly proved is that you don't have to take your chances with fetal cells. You can wait until the litter has grown up, see which individuals have proved themselves to be great producers of wool, milk or--a stretch, perhaps--NBA titles, and then clone the champs.

Still, Dolly would be just a laboratory curiosity if no one could repeat Wilmut's breakthrough. And that's where Teruhiko Wakayama comes in. He's a 31-year-old Japanese postdoctoral student who was studying cloning as a hobby at the University of Hawaii, where his lab director, Ryuzo Yanagimachi, was famous for telling students "not to be afraid of asking crazy questions. The crazier the better."

Wakayama's idea was truly crazy: he wanted to clone mice, long believed to be among the worst candidates for cloning because their egg cells are particularly delicate and their embryos develop so rapidly. He squeezed in the cloning work during his free time, carefully manipulating one type of mouse cell after another until, just months after Dolly was unleashed on the world, he succeeded in cloning the cumulus cells that surround the egg in the ovary. Wakayama's whimsical name for his new creation: Cumulina.

His technique was almost identical to Wilmut's except for two key steps. First, instead of using electric shocks to coax an adult cell into merging with a host egg whose nucleus had been removed, Wakayama injected just the adult nucleus into a nucleus-free host. And second, he let the hybrid cell sit for up to six hours before stimulating it to start dividing.

He must have done something right. Where Wilmut got only a single cell to flower into an embryo and then a full-term fetus, Wakayama got dozens; up to 3% of his clones survived. That may be in part because his technique treated the cells more gently. It's also possible that injecting just the nucleus introduced fewer contaminants into the host cell.

Whatever the reason, the cloned mice were perfectly normal in all respects. They could mate and give birth, and their DNA was so robust that they themselves could be cloned--and their clones cloned. So far, Wakayama and his colleagues at the University of Hawaii have produced three generations of identical mice, 50 in all.

A reliable cloning technique for an animal that has such well understood genetics and reproduces so rapidly (up to five generations in a year) means that scientists will be able to study in detail the process by which genes turn on and turn off, and thus how cells become specialized for particular jobs in the body. And if Wakayama's technique can be scaled up to larger animals--a question researchers are already making plans to answer--the research could lead to all sorts of applications.

Cows genetically engineered to produce valuable human proteins, for example, or pigs whose organs have been altered to remove proteins that trigger rejection after transplant operations, could be stamped out on an assembly line. Fast racehorses or blue-ribbon pets might be duplicated at will. In humans, both cancer and the aging process involve genetic changes at the cellular level. Thus a better understanding of how genes work might someday have implications for anti-cancer and anti-aging treatments.

It's even conceivable that a human with a failing liver could have a new one grown from, say, a cell taken out of his bone marrow. "This is fantasy now," admits Alan Colman, research director of PPL Therapeutics, the Scottish biotechnology firm that holds the license for the process that created Dolly. "But two years ago, so was the work that is now being presented in Nature."

And yes, Wakayama's work does bring complete human cloning a dramatic step closer to reality. Creating a carbon copy of a living adult will always be impossible, however. The difference in age between parent and child alone would prevent it, and because genetics only partly determines who we are, a clone could never be exactly the same person as its parent. The offspring of a brilliant musician or a scientific genius could, depending on his or her life experience, turn out to be a great criminal. But human cloning will happen anyway--perhaps much sooner than anyone thought. And when it does, the hand-wringing of ethicists and politicians will not have been wasted.

--Reported by Helen Gibson/London and Alice Park/New York

With reporting by Helen Gibson/London and Alice Park/New York