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Embryonic Stem Cells Generated Through Novel Technique: Scientists

Posted on: Monday, 17 October 2005, 09:00 CDT

Embryonic stem cells generated through novel technique: scientists

LOS ANGELES, Oct. 16 (Xinhua) -- A new technique has generated embryonic stem cells in mouse experiments, scientists reported on Sunday.

During the novel procedure, called altered nuclear transfer (ANT), researchers first create genetically altered embryos that are unable to implant in a uterus, and then extract stem cells from these embryos.

Because the embryos cannot implant, they are by definition not "potential" human lives, thus the ethical debates around the stem cell research would be avoided, scientists suggested in two papers in the online issue of the journal Nature.

"The purpose of our study was to provide a scientific basis for the ethical debate," said Rudolf Jaenisch, lead author of one Nature paper at the Whitehead Institute for Biomedical Research.

"Our work is the first proof-of-principle study to show that altered nuclear transfer not only works but is extremely efficient."

ANT has been described as an ethical alternative to the current somatic cell nuclear transfer (SCNT) technique, also known as therapeutic cloning.

For the SCNT, a donor nucleus is implanted into an egg cell from which the nucleus had been removed. This egg cell is then tricked into thinking it has been fertilized. That causes it to grow into a blastocyst, a mass of about 100 cells, from which stem cells are removed.

These embryonic stem cells can divide and replicate themselves indefinitely, and they can also form any type of tissue in the human body. However, to cull these stem cells, the blastocyst must be destroyed, which some critics insist is tantamount to destroying a human life.

The novel ANT procedure is similar to SCNT, but with one crucial twist -- before the donor nucleus is transferred into the egg cell, its DNA is altered so that the resulting blastocyst has no chance of ever becoming a viable embryo. As a result, a "potential human being" is not destroyed once stem cells have been extracted.

Jaenisch's group focused on a gene called Cdx2, which enables an embryo to grow a placenta. In order to create a blastocyst that cannot implant in a uterus, the researchers disabled Cdx2 in mouse cells.

They accomplished this with a technique called RNA interference, or RNAi, to target an individual gene and disrupt its ability to produce protein. In effect, the gene is shut off.

Once the stem cells had been extracted from the blastocysts, Cdx2 was still disabled in each of these new cells, something that needed to be repaired in order for these cells to be useful.

To correct this, the researchers deleted the inserted RNA molecule by transferring a plasmid into each cell. The stem cells resulting from this procedure proved to be just as robust and versatile as stem cells procured in the more traditional fashion.

In another study, researchers from the Advanced Cell Technology borrowed a lab technique used in fertility clinics, called pre- implantation genetic diagnosis, or PGD. It is used to screen embryos for genetic disorders.

They plucked a single cell from eight-cell mouse embryos, which were about two days old. While fertility clinics use such a cell for genetic testing, the researchers cultured the plucked cells and found they behaved like embryonic stem cells. The embryos, meanwhile, went on to produce mice.

The result suggested that when clinics do PGD, they could let the cell they remove divide into two, and use one resulting cell for genetic testing and the other to establish a stem cell line.

Source: Xinhua News Agency - CEIS

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