US: A biological quirk in the cells of primates may make human cloning impossible, scientists said yesterday.
Researchers have found a fundamental molecular obstacle to reproductive cloning. The discovery was made by Prof Gerald Schatten, the same scientist who, three years ago, announced the birth of the world's first primate "clone" - a rhesus macaque monkey called Tetra. But Tetra was created by simply splitting an original embryo, the same way that nature produces twins.
No one has ever succeeded in cloning a primate by replacing the nucleus in an egg with one from a donor cell.
Only "true" cloning by nuclear transfer - the same technique used to create Dolly the Sheep - can theoretically produce an unlimited number of clones.
Prof Schatten said yesterday this may never be possible either in monkeys and apes or humans.
The reason is that a basic mechanism behind cell division appears to be flawed in primate cloning. As a result, development of a cloned primate embryo is never allowed to get past the initial stage. "The chromosomes do not split properly," said Prof Schatten, from the University of Pittsburgh School of Medicine in Pennsylvania, US. "From the very first cell division, cell development is inappropriate in vital ways."
Prof Schatten and his team transferred donor nuclei to 724 eggs taken from female rhesus macaques. Although 33 embryos were implanted in the wombs of surrogate mothers after initial cell division, none produced a pregnancy. - (PA)