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October 16, 2002
Cloning's Growing Pains
Ian Wilmut and his colleagues have an interesting review in a recent issue of Nature (no web link) on the status of mammalian cloning. It's still so difficult that it almost qualifies as a stunt. Several species have had the nuclear-transfer technique that produced Dolly the sheep applied successfully (if you can use that word for a technique that has at least a 95% failure rate.) But others haven't, and it's not clear why some work and some don't (for example, mice and rats, respectively.)
What the article makes very clear is that the animals produced in this way are far from normal, and that we don't even have a good handle on the extent of their abnormalities yet. (In cases like cattle, we're going to have to wait years to see how they age, for one thing.) They point out that close examination of even the young cloned animals turns up differences, many of which are probably deleterious.
Why all the problems? Shouldn't the genetic material in the new nucleus just pop right into the cell and go to work? These experiments have been a dramatic demonstration that any scheme that treats a cell and its nucleus as separate entities has serious shortcomings. There are epigenetic influences at work (changes in inheritance by means other than changing DNA sequence,) and we're just barely starting to understand them. Subtle chemical changes in the DNA bases and their associated proteins can lead to large differences down the line, and it appears that some of these signals get scrambled and mismatched during the nuclear transfer.
These are not secrets; the workers in this area have been very upfront about all these problems. (Wilmut published an article not long ago titled "Are There Any Normal Cloned Mammals?") Many researchers are using the technique because these problems exist, actually - it's a good way to study phenomena that would otherwise be hard to unravel. But all this makes me think that those persistant reports of a cloned human baby are probably nonsense.
They'd better be. With the state of the art being what it is, anyone who has actually tried this on humans is going to have a lot to answer for.
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