Questions raised over cloned puppy
Is Snuppy really a clone? With the credibility of his creator Woo Suk Hwang under fire, the dog's credentials are being challenged.
The Afghan hound was supposedly the first dog to be cloned (B. C. Leeet al. Nature 436, 641; 2005 ). Cloning dogs presents unusual challenges because, compared with other mammals, the egg cells are difficult to mature in vitro. Hwang's group says it used the same technology as in its human experiments — removing the nucleus from a donor's cell and inserting it into an egg cell, a process called somatic-cell nuclear transfer (SCNT).
But Robert Lanza, a stem-cell expert at Advanced Cell Technology in Worcester, Massachusetts, and a competitor with Hwang in human therapeutic cloning, says the paper should now be seriously re-examined.
Lanza says that Snuppy, seen on the right with the dog from which he was supposedly cloned, might have been created by a technique called embryo splitting, in which cells from an early-stage embryo are divided and then implanted separately. The technique creates identical twins. One set of cells could have been used immediately to create a dog while another was frozen and stored. If the frozen cells were later used to create a dog with identical DNA, that could be presented as an SCNT clone.
Such trickery could be caught by examining mitochondrial DNA, which is passed maternally with the egg cell. If Snuppy were really a SCNT clone, he should have the mitochondrial DNA of the dog from which the egg was taken. If he's a fake, he'd share it with the dog from which he was supposedly cloned.
Mitochondrial DNA data have not been part of previous cloning papers, and were not presented in Nature. Lanza suggests that it would now be a good idea to do the test. “If the mitochondrial DNA is the same, that's the end of that paper,” says Lanza.
Nature is starting an investigation, including a mitochondrial DNA test, that is unlikely to be complete before January 2006.