Cloning monkeys

A team of American scientists has produced the first non-human primate clone. Tetra, a Rhesus monkey baby, was born in September last year at the Oregon Regional Primate Research Center in the US. However, the creation of Tetra was not, done by nuclear transfer as Dolly the sheep was. Instead, embryo splitting was used to create identical embryos, of which Tetra was one.

During the research, 107 Rhesus embryos were split in total, and in the case of Tetra, an eight-cell embryo from which the shell had been removed, was "mechanically disrupted" to form four individual two-cell embryos. Two of these embryos were implanted into each of two surrogate mothers one of whom miscarried. The second monkey had an uneventful pregnancy and became Tetra's "mother".

The implications of this mode of "cloning" are great for medical research. Gerald Schatten, leader of the Oregon team has pointed out that a group of sheep clones created by nuclear transfer all differ in size and temperament. There have also been concerns about the affect mitochondria from enucleated eggs may have on nuclear transfer clones. Embryo splitting produces genetically identical offspring valuable to medical research as it may reduce the number needed for some experiments and create new opportunities to study disease and new treatments.

The aim of the research and development of these "true clones" is to produce models for testing whether it is possible to grow stem cells for transplant into patients with failing organs. Most new medical techniques are tested on mice. Monkeys, being genetically more similar to humans, may provide more reliable results. However, the research has inevitably re-sparked the debate over the possibilities and implications of human cloning and the ethics of human stem cell research.

Monkey embryo cloning success

A US scientist who suggested that attempts to clone primates might never succeed using current technology has created cloned monkey embryos. Gerald Schatten and his colleagues transferred the embryos into female monkeys, but none of the resulting pregnancies lasted more than a month. The team, based at the University of Pittsburgh, reported their work at the American Society for Reproductive Medicine (ASRM) in Philadelphia last week.

In 2003, Schatten's group reported that attempts to clone primates, including humans, may never succeed using the technique used to create Dolly the sheep and other cloned mammals. Somatic cell nuclear transfer (SCNT) involves removing the genetic information of an unfertilised egg cell, and replacing it with that of a body cell. The researchers found that vital "spindle" proteins are lost from the egg during the procedure, which mean that the cell's genetic information cannot be passed on correctly when the cell divides. The team created 716 cloned rhesus monkey embryos, but all had an abnormal number of chromosomes, and failed to grow. At the time, Schatten said: "I hope this natural obstacle affords us time to make responsible and enforceable legislation to prevent anyone attempting human reproductive cloning".

However, less than a year later, in February 2004, scientists in South Korea announced their success in creating cloned human embryos. Using a modified version of the nuclear transfer technique, the team, based at the Seoul National University, created 30 cloned human embryos. The researchers extracted stem cells from 20 of these, from which they managed to grow one human embryo stem (hES) cell line. The research was a breakthrough for "therapeutic cloning" research, which aims to use cloned embryo stem cells to develop tissue-matched cell therapies for a range of different diseases.

Using the Korean team's method, Schatten's team managed to create 135 cloned monkey embryos, using the genetic material from adult skin and cumulus cells, which surround the developing egg in the ovary. Schatten says he isn't sure why the technique worked, although it could be because it involves gently squeezing out the egg nucleus (which contains its genetic material), rather than sucking it out. This may cause less damage to the egg, or could mean that the crucial spindle proteins are left behind.

Schatten says it is too early to say whether cloned monkeys will ever be born, and the results cannot be used to predict if cloned human babies could survive long in development. But, he says, his work does confirm that the Korean cloning method works, showing that "at least part of the technique is reproducible".