New Ways to Generate Embryonic Stem Cells

Both methods were described in the October 16, 2005, online edition of Nature.

One method, called altered nuclear transfer (ANT), was developed by scientists at the Massachusetts Institute of Technology and the Whitehead Institute for Biomedical Research (MIT, Cambridge, MA, USA) as an ethical alternative to somatic cell nuclear transfer (SCNT), or therapeutic cloning. This method is similar to SCNT but before the donor nucleus is transferred into the egg cell, its DNA is altered so that the resulting blastocyst has no chance of becoming a viable embryo or human being.

The scientists used RNA interference (RNAi) to shut off a gene called Cdxx2, which enables an embryo to grow a placenta. Once the stem cells had been extracted from the blastocysts, the siRNA molecule was deleted by transferring a plasmid into each cell. Stem cells resulting from this procedure proved to be just as robust and versatile as stem cells procured in the traditional way.

"Our work is the first proof-of-principle study to show that altered nuclear transfer not only works but is extremely efficient,” said lead author Rudolf Jaenisch, professor of biology at MIT.

The second method was developed by researchers at Advanced Cell Technology, Inc. (ATC, Worcester, MA, USA). They used a method of deriving stem cells in mice using a single-cell embryo biopsy similar to a method used in preimplantation genetic diagnosis. This technique does not interfere with the developmental potential of embryos. After implantation into a mouse womb, the embryo survived and developed into a baby mouse. The researchers say this method could be used with human embryos.

"In the past, stem cell lines have been isolated from the inner cell mass of blastocysts and in a few instances, from earlier, cleavage-stage embryos,” noted first autor Young Chung, senior scientist at ATC. "We generated five embryonic stem (ES) cells and seven trophoblast stem (TS) cell lines from single mouse embryo cells. The stem cells were able to generate all the cell types of the body, including nerve cells, bone, and beating heart.”





Related Links:
Whitehead Inst./MIT
Advanced Cell Technology, Inc.