A team at the Roslin Institute near Edinburgh has coaxed six eggs to develop into early-stage embryos as if they had been fertilised by a sperm. The experiment could help to realise the medical promise of embryonic stem (ES) cells.

While both eggs and sperm are needed for normal sexual reproduction, eggs can start to develop spontaneously in a process known as parthenogenesis, a term that comes from the Greek for virgin birth. All fungi, most plants and many animals, including lizards, bees, corals and some birds, can have normal offspring in this way.

In mammals, including human beings, parthenogenesis never leads to the birth of young, but it does lead occasionally to the development of an embryo that dies at a very early stage. In rarer cases these “parthenotes” can blend with a normal embryo that develops to term as a hybrid known as a chimera.

Last year the Roslin team led by Paul de Sousa was given permission by the Human Fertilisation and Embryology Authority to attempt to trigger parthenogenesis in human eggs. It has now produced six parthenotes that have grown for five days to reach the blastocyst stage, Dr de Sousa told the BA Festival of Science in Dublin yesterday.

Scientists have long been interested in exploiting parthenogenesis as a new source of human embryos for use in research. Some opponents of experiments on normal embryos are less concerned about the destruction of parthenotes, which are not capable of forming living people, and peculiar aspects of their development also offer insights that could advance other areas of human biology.

Parthenogenetic embryos could also be a source of ES cells, which have the ability to generate any tissue type in the human body and potentially could be used to grow replacement cells to treat conditions such as Parkinson’s disease and diabetes. ES cells taken from a parthenote would be genetically similar to the woman who provided the egg, and may be less likely to be rejected by her immune system.

There are concerns, however, that ES cells produced by parthenogenesis may be too abnormal for use in therapy and that they are unlikely to be suitable for treating men or older women who have no eggs.

Dr de Sousa’s team obtained about 300 immature eggs, donated by women having sterilisation surgery to have their Fallopian tubes tied. About half of these eggs were matured in the laboratory, and about 5 per cent were coaxed to divide parthenogenetically with an electric current and growth factors. The result was the production of six parthenogenetic blastocysts.

Dr de Sousa has attempted to derive ES cells from these embryos but has so far failed. The eggs that did divide were coaxed with chemicals to keep a set of genes that would otherwise have been jettisoned, known as the polar body, so that it would have a full complement of chromosomes.

Dr de Sousa said that the aim of the research was to generate ES cells so their development could be studied. Cells of parthenotes carry errors in the way genes are switched on and off, and as this is also a problem with cloned ES cells scientists are keen to investigate further.

“We want these cell lines mainly for research,” he said. “Both cloning and parthenogenesis create cells with perturbations, and it is entirely possible that these will mean cloned stem cell lines are not suitable for therapy or research models.”

There is no intention to implant any parthenogenetic embyros in women’s wombs. The scientists will not consider using any stem cells derived in treatment until much more work has been done to determine that they will be safe.

Other potential benefits of the research include improving understanding of imprinting — a process that controls how genes inherited from the mother and father are used in the body. This is thought to be one of the chief reasons cloned and parthenogenetic cells are abnormal.

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