UCSF scientists are reporting what they say is a significant improvement in the technique for genetically reprogramming mouse cells to their embryonic state, a process that transforms the cells, in essence, into embryonic stem cells.
The finding, published on-line as an immediate early publication in “Cell Stem Cell” (Sept. 6, 2007), builds on the strategic breakthrough reported by Shinya Yamanaka, MD, PhD, in 2006, and confirmed in the spring of 2007 both by Yamanaka's team and, in independent studies, by scientists at MIT, Harvard and UCLA.
The advance by the UCSF team should accelerate research aimed at improving the original strategy, the team says, and increase its potential use for studying disease development and creating patient-specific stem-cell based therapies.
The work is the result of a collaboration between the labs of Miguel Ramalho-Santos, PhD, and Robert Blelloch, MD, PhD, of the UCSF Institute for Regeneration Medicine.
“The new technique removes a major technical hurdle that has likely discouraged many labs around the world from carrying out studies on the strategy,” says senior author Ramalho-Santos, a UCSF Fellow and a member of the Diabetes Center. For separate reasons, he says, removal of the hurdle increases the technique's potential use in developing patient-specific cellular therapies.
“Now, laboratories will be able to use the approach to study a broad range of normal and diseased cells of interest,” says the first author of the study, Blelloch, an assistant professor of urology. “There will be a much greater ability to precisely dissect the mechanisms of reprogramming and to identify the genes that will be most effective in transforming adult cells.”
Yamanaka's strategy -- over-expressing certain genes in mouse skin cells to initiate reprogramming – relied on the insertion of a foreign “drug resistance” gene into the mouse skin cells. This gene would “switch on” in those cells that successfully converted to embryonic stem cells, thus providing a means of detecting them. The drawbacks of this technique were that it was technically difficult to carry out and, because it involves a foreign gene, would raise safety concerns that would hinder its use in cell-based therapies.
In the current study, the UCSF scientists developed an alternative to this genetically engineered “switch” technique. They developed serum-free conditions in the cell culture dish that both promoted more successful reprogramming and generated embryonic stem cells that could be detected based on their form and structure, alone.
Scientists are interested in reprogramming because of its potential for developing human embryonic stem cells that contain the genetic makeup of individual patients. In theory, any patient's cell, say, a skin cell, could be reprogrammed. If the resulting embryonic stem cell could then be prompted in the culture dish to specialize into one of the various cell types of the body, such as of the heart, lung and brain, the resulting cells could provide the starting point for a host of clinical-research strategies.
Researchers could create dopamine-producing cells from Parkinson's disease patients and study them in the culture dish to learn the earliest steps of disease development. They could also test experimental drugs on such cells in the culture dish.
Alternatively, they could generate healthy specialized cells from patients who had donated their genetic material, and transplant them into tissues -- without the risk of prompting immune rejection -- to treat failing hearts, neurological diseases such as Parkinson's disease and amyotrophic lateral sclerosis, spinal cord injury and diabetes.
The reprogramming strategy pioneered by Yamanaka -- who in August began his transition from Kyoto University to the UCSF-affiliated Gladstone Institute of Cardiovascular Disease and UCSF -- involved over-activating four genes in mouse skin cells in the culture dish. His team showed that over-expressing these genes – oct4, sox2, klf4 and c-myc – can cause the full complement of genes in mouse cells to lose their adult functions and begin functioning as they would have as embryonic stem cells. Yamanaka named these cells “induced pluripotent (iPS) cells.”