Human cloning impossible?

Attempts to clone primates, including humans, may never succeed using current technology, according to a new US study. A group of researchers at the University of Pittsburgh has found that vital proteins are lost from the egg during the nuclear transfer procedure, the technique used to create Dolly the sheep. Their results were published in last week's Science.

Several different species of mammals have been cloned using SCNT (somatic cell nuclear transfer ) techniques, in which the genetic material of an egg cell is replaced with that of a single embryo or adult body cell. In the latest study, the scientists created 716 cloned rhesus monkey embryos, but all of them failed to develop. They found that the embryos were missing at least two proteins vital for the 'spindle', the cellular apparatus that ensures a dividing cell passes on identical sets of genetic information to its daughter cells. As a result, all the embryo cells had abnormal numbers of chromosomes, so the cloned embryos could not grow. It seems that in primates, these proteins are attached to the chromosomes in the egg cell, which are removed during SCNT. In other animals, the key proteins are scattered throughout the egg, so enough remain to enable cell growth and division to proceed. 'I hope this natural obstacle affords us time to make responsible and enforceable legislation to prevent anyone attempting human reproductive cloning' said team leader Gerald Schatten.

A pair of bantengs, an endangered species of Asian cattle, were born in the US last week, after being cloned from an animal that died over 20 years ago. One is healthy, but the other had to be put down because it was abnormally large. The clones were produced by biotech firm Advanced Cell Technologies, using tissue stored at San Diego Zoo's 'frozen zoo'.