Older embryos can survive stem-cell extraction
Mouse study suggests stem-cell work could be made more efficient.
US researchers say they have improved the technique by which stem cells can be coaxed from an embryo without harming it.
The technique has been used only on mouse embryos and is still being refined. But it might improve attempts to make embryonic stem (ES) cell lines without destroying human embryos.
Researchers are keen to create human ES cells because they can give rise to many different tissue types that could help cure diseases. Extracting the cells usually kills the embryo, which some find morally unacceptable.
Earlier this year, a group led by Robert Lanza at Advanced Cell Technologies in Worcester, Massachusetts, said they had grown ES cells from single cells taken from human embryos of 8-10 cells1. Single cells are sometimes extracted from embryos during in vitro fertilization, and the embryo goes on to become a child. So in theory, Lanza's method should allow for a stem-cell line and a baby to develop from the same embryo. The team derived ES cell lines from 2 of 91 cells, or just over 2%.
Takumi Takeuchi and his colleagues at Weill Medical College in New York say they have made this process more efficient in mice at least.
The researchers used slightly older embryos that have formed into hollow balls called blastocysts. These consist of a clump of 20-25 cells called an inner cell mass, which will give rise to the embryo, circled by cells that will form the placenta and supporting tissues. Normally, the entire inner cell mass is extracted and grown into ES cells, killing the embryo.
Takeuchi and his team extracted blastocysts from mice and used an enzyme to soften the natural glue holding the inner cell mass together. They then took one, two or three cells and tried to grow these into ES cells, before implanting the embryos back into the mice.
Three-cell extractions led to ES cell lines, but not one or two cells. Using the technique, the researchers grew four ES cell lines from 16 blastocysts a success rate of 25%. This is a better rate than both Lanza's and the conventional technique.
After extracting the three cells and implanting the embryos back into mothers, 54% of them developed into normal mouse pups. In a control group of blastocysts that were removed from mice and replaced without taking away any cells, 62% of embryos developed into pups.
This suggests that the procedure may have an impact on the survival of the embryos, but Takeuchi says this is not a statistical difference.
Group leader Gianpiero Palermo says that he and his colleagues are working to improve the technique. They presented their results at the American Society for Reproductive Medicine meeting in New Orleans, following on preliminary results presented at another conference in June of this year (see ' Philosophical approach').
If such methods will work in humans without damaging the embryo, then women using in vitro fertilization could use this technique to grow ES cells for research or, perhaps, to bank for their child.
Like other suggestions on how to create ES cells, this one is unlikely to eliminate all possible ethical objections. Although the mice appeared normal after the procedure, they might have subtle defects. Palermo says that he wants to test this with genetic analyses on the baby mice.
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- Klimanskaya I., et al. Nature, AOP . doi:10.1038/nature05142 (2006).
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