July 3, 2014
Nuclear Transfer Proven An Effective Method In Stem Cell Production
redOrbit Staff & Wire Reports - Your Universe Online
A new process known as “somatic cell nuclear transfer” is far better and much more accurate when it comes to coaxing embryonic stem cells out of human skin tissue, according to new research appearing in Tuesday’s edition of the journal Nature.Scientists from Oregon Health & Science University (OHSU), the University of California-San Diego (UCSD) School of Medicine and the Salk Institute for Biological Studies created stem cells using two different methods: nuclear transfer, which involves moving genetic material from a skin cell into an empty egg cell, and a more traditional method in which activating a small number of genes reverts adults cells back to an embryonic state.
Experts believe that stem cell therapies could someday be used to replace human cells damaged through injury or illness, including spinal cord injuries, diabetes, Parkinson's disease and multiple sclerosis. Human embryonic stem cells (ES cells), which are cells cultured from discarded embryos, are viewed by scientists as the “gold standard” of the field, and the new study reports that somatic cell nuclear transfer (SCNT) more closely resembled ES cells.
This marks the first time that researchers had directly compared the SCNT method with the induced pluripotent stem cell (iPS cell) technique, and in a statement, co-senior author and UCSD assistant professor in reproductive medicine Dr. Louise Laurent explained that the nuclear transfer ES cells were “more completely reprogrammed” and had “fewer alterations in gene expression and DNA methylation levels” than the iPS cells.
Access to actual human embryonic stem cells (hESCs) has been limited in the US due to ethical and logistical issues, forcing researchers to devise other methods to create stem cells, the study authors explained. Typically, that means creating iPS cells by taking adult cells and adding in a mixture of genes that regress those cells to a pluripotent stem-cell state. Those cells can then be coaxed into cells resembling those found in the heart or brain.
Over the past year, however, an OHSU-led team of researchers have built upon somatic cell nuclear transfer (the same technique used for cloning organisms) to transplant the DNA-containing nucleus of a skin cell into an empty human egg. Once completed, the combination naturally matures into a group of stem cells.
For the first time, the OHSU, UCSD and Salk Institute researchers conducted a direct, in-depth comparison of the two different methods. They created four nuclear transfer ES cell lines and seven iPS cell lines using the same skin cells as the donor genetic material source, and then compared them to a pair of standard human ES lines.
A battery of standard tests revealed that all 13 cell lines were shown to be pluripotent. However, when the researchers used powerful genomic techniques to take a closer look at the DNA methylation (a biochemical process responsible for turning genes on or off) and the gene expression signatures of each cell line, they discovered that the nuclear transfer ES cells more closely resembled those of ES cells than did iPS cells in both characteristics.
“If you believe that gene expression is important, which we do, then the closer you get to the gene expression patterns of embryonic stem cells, the better. Right now, nuclear transfer cells look closer to the embryonic stem cells than do the iPS cells,” co-senior author Joseph R. Ecker, director of the Salk Institute's Genomic Analysis Laboratory and co-director of the Center of Excellence for Stem Cell Genomics, said in a statement.
Despite the results, Ecker explained that he did not expect to see a large increase in the use of nuclear transfer protocols – in part because the method is one that falls into restricted for federal funding purposes. However, he believed that their findings could be adapted to improve the protocols used in the production of iPS cells, provided scientists can determine exactly what component of an egg helps spur on the growth of pluripotent stem cells.