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Mammalian eggs created from embryonic stem cells

By Our Special Correspondent

CHENNAI MAY 3. Researchers at the University of Pennsylvania have created the first mammalian gametes (mature egg or sperm) grown in vitro directly from embryonic stem cells. The work, in which mouse stem cells placed in glass dishes — without any special growth or transcription factors — grew into oocytes (an egg before the completion of maturation) and then into embryos, was published in the recent issue of the journal Science.

The results have demonstrated that even outside the body the embryonic stem cells remain totipotent, or are capable of generating any of the body's tissues. It remains to be seen if this great feat can be replicated with human embryonic stem cells.

In parthenogenesis, or spontaneous reproduction without sperm, the nucleus from any body cell is removed and implanted into an egg before the egg is made to divide without being fertilized by a sperm. This method of producing embryonic stem cells had raised several ethical issues. This procedure makes these ethical concerns a non-issue.

The recent achievement has proved many scientists wrong, as it was generally believed that it was impossible to grow egg or sperm from stem cells outside the body. All earlier attempts have yielded only somatic cells (any cell found in the body except egg or sperm). The latest attempt has not only succeeded in producing eggs from mouse embryonic stem cells but the eggs so produced underwent cells division (meiosis) too. Structures similar to the follicles that surround and nurture natural mouse eggs were also formed and the culmination was the development into embryos.

The scientists found the cells organising into colonies of variable size after 12 days in culture. Shortly thereafter, individual cells detached from these colonies. The germ cells then accumulated a coating of cells similar to the follicles surrounding mammalian eggs. Starting on day 26, egg-like cells were released into the culture — similar to ovulation — and by day 43, embryo-like structures arose through parthenogenesis, or spontaneous reproduction without sperm.

Certain countries such as Germany may have to rework on their legislation if scientists are to do an encore with human embryonic stem cells. It was assumed that the potency of stem cells outside the body was limited, thus prompting Germany to ban research with totipotent stem cells.

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