SCIENTISTS have succeeded in coaxing embryonic stem cells to develop into eggs, in experiments on mice that could sidestep some of the ethical concerns about therapeutic cloning technology.

Research in the United States and France has discovered that the master cells from embryos are capable not only of forming every type of normal tissue, as has been known for some time, but that they can make reproductive cells as well. Some of these “artificial eggs” even went on to develop spontaneously into embryos, without fertilisation by sperm, through a process known as parthenogenesis. Mouse embryos that were formed this way developed normally for a few days, but never survived to birth in the womb.

If the capability exists in human beings as well as mice, it could be exploited to provide a plentiful source of artificial eggs and embryos for research into therapeutic cloning — the practice of growing “spare part” tissue for treating disease. It would be a cheaper alternative to donated eggs, which are in short supply, and many bioethicists also believe their use would pose fewer moral difficulties. “This paper is an ethical earthquake,” Arthur Caplan, a bioethicist at the University of Pennsylvania, said. “If these cells could be a source of human oocytes (eggs), scientists might be able to use them rather than eggs from human donors.”

Others, however, feel that cells derived in this way will remain ethically problematic, particularly for religious groups, as the stem cells from which they are initially produced originate from embryos.

In the study, led by Karin Hübner and Hans Schöler of the University of Pennsylvania, researchers took ordinary stem cells from mouse embryos and watched as they developed. No special growth factors were added, but the cells were marked with a fluorescent dye to identify any that developed into reproductive cells, also known as gametes. After eight days up to 40 per cent of the cells had made the transformation.

It is not yet known whether the artificial eggs can be fertilised by sperm in the normal way, the scientists report today in the journal Science. If the eggs can be fertilised normally and develop into healthy offspring, the technique might eventually be used in fertility treatment.

The team now plans to attempt to transplant the nuclei of adult cells into their artificial eggs, using the cell nuclear transfer cloning technique. If this works it would produce a plentiful supply of stem cells, matched to the tissue from which the donated nucleus was taken, that could then be grown into spare part tissues.

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