Tuesday, 20 November 2007

Yamanaka Turns Human Fibroblasts to ESC-like Cells

Simple recipe turns human skin cells into embryonic stem cell-like cells Tuesday, 20 November 2007 A simple recipe — including just four ingredients — can transform adult human skin cells into cells that resemble embryonic stem cells, researchers report in an immediate early publication of the journal Cell, a publication of Cell Press. The converted cells have many of the physical, growth and genetic features typically found in embryonic stem cells and can differentiate to produce other tissue types, including neurons and heart tissue, according to the researchers. They added, however, that a comprehensive screen of the activity of more than 30,000 genes showed that the so — called “induced pluripotent stem (iPS) cells” are similar, not identical, to embryonic stem cells. "Pluripotent" refers to the ability to differentiate into most other cell types. The chemical cocktail used in the new study is identical to one the team showed could produce iPS cells from adult mouse cells in another Cell report last year. That came as a surprise, said Shinya Yamanaka of Kyoto University in Japan, because human embryonic stem cells differ from those in mice. Those differences had led them to suspect "that some other factors might be required to generate human iPS cells,” he said. The findings are an important step forward in the quest for embryonic stem cell — like cells that might sidestep the ethical stumbling blocks of stem cells obtained from human embryos. He emphasized, however, that it would be “premature to conclude that iPS cells can replace embryonic stem cells.” Embryonic stem cells, derived from the inner cell mass of mammalian blastocysts — balls of cells that develop after fertilization and go on to form a developing embryo — have the ability to grow indefinitely while maintaining pluripotency, the researchers explained. Those properties have led to expectations that human embryonic stem cells might have many scientific and clinical applications, most notably the potential to treat patients with various diseases and injuries, such as juvenile diabetes and spinal cord injury. The use of human embryos, however, faces ethical controversies that hinder the applications of human embryonic stem cells, they continued. In addition, it is difficult to generate patient or disease — specific embryonic stem cells, which are required for their effective application. One way to circumvent these issues is to induce pluripotent status in other cells of the body by direct reprogramming, Yamanaka said. Last year, his team found that four factors, known as Oct3/4, Sox2, c-Myc, and Klf4, could lend differentiated fibroblast cells taken from embryonic or adult mice the pluripotency normally reserved for embryonic stem cells. Fibroblasts make up structural fibers found in connective tissue. Those four factors are “transcription factors,” meaning that they control the activity of other genes. They were also known to play a role in early embryos and embryonic stem cell identity. The researchers have now shown that the same four factors can generate iPS cells from fibroblasts taken from human skin. “From about 50,000 transfected human cells, we obtained approximately 10 iPS cell clones,” Yamanaka said. “This efficiency may sound very low, but it means that from one experiment, with a single ten centimetre dish, you can get multiple iPS cell lines.” The iPS cells were indistinguishable from embryonic stem cells in terms of their appearance and behaviour in cell culture, they found. They also express genetic markers that are used by scientists to identify embryonic stem cells. Human embryonic stem cells and iPS cells display similar patterns of global gene activity. They showed that the converted human cells could differentiate to form three “germ layers” in cell culture. Those primary germ layers in embryos eventually give rise to all the body’s tissues and organs. They further showed that the human iPS cells could give rise to neurons using a method earlier demonstrated for human embryonic stem cells. The iPS cells could also be made to produce cardiac muscle cells, they found. Indeed, after 12 days of differentiation, clumps of cells in the laboratory dishes started beating. The human iPS cells injected under the skin of mice produced tumours after nine weeks. Those tumours contained various tissues including gut — like epithelial tissue, striated muscle, cartilage and neural tissue. They finally showed that iPS cells can also be generated in the same way from other human cells. “We should now be able to generate patient — and disease — specific iPS cells, and then make various cells, such as cardiac cells, liver cells and neural cells,” Yamanaka said. “These cells should be extremely useful in understanding disease mechanisms and screening effective and safe drugs. If we can overcome safety issues, we may be able to use human iPS cells in cell transplantation therapies.” Shinya Yamanaka is also a senior investigator at the Gladstone Institute of Cardiovascular Disease (GICD), an independent, non-profit biomedical research organization affiliated with the University of California, San Francisco. “The rapid application of this approach to human cells has dramatically changed the landscape of stem cell science,” said GICD Director Deepak Srivastava, MD. “Dr. Yamanaka’s work is monumental in its importance to the field of stem cell science and its potential impact on our ability to accelerate the benefits of this technology to the bedside. Not only does this discovery enable more research, it offers a new pathway to apply the benefits of stem cells to human disease.” “Dr. Yamanaka and his group have made yet another extremely important contribution to the stem cell field,” said Richard Murphy, interim president of the California Institute for Regenerative Medicine (CIRM). “Their results open the door to generating alternative sources of pluripotent cells from patients, which is a major step forward. However, much work still needs to be done to fully characterize and understand the capacity of these induced pluripotent cells to study and to treat human diseases.” CIRM’s Murphy added, “Dr. Yamanaka’s work, which uses viral vectors to introduce into cells pluripotency-associated genes, further emphasizes the critical need we have to continue working with naturally occurring human embryonic stem cells, which remain the gold standard against which all alternative sources of human pluripotent stem cells must be tested.” Reference: Induction of Pluripotent Stem Cells from Adult Human Fibroblasts by Defined Factors The researchers include Kazutoshi Takahashi, Kyoto University, in Kyoto, Japan; Koji Tanabe, of Kyoto University, in Kyoto, Japan; Mari Ohnuki, of Kyoto University, in Kyoto, Japan; Megumi Narita, of Kyoto University, in Kyoto, Japan, and the Japan Science and Technology Agency, in Kawaguchi, Japan; Tomoko Ichisaka, of Kyoto University, in Kyoto, Japan, and the Japan Science and Technology Agency, in Kawaguchi, Japan; Kiichiro Tomoda, of the Gladstone Institute of Cardiovascular Disease, San Francisco, CA, USA; and Shinya Yamanaka, of Kyoto University, in Kyoto, Japan, the Japan Science and Technology Agency, in Kawaguchi, Japan; and the Gladstone Institute of Cardiovascular Disease, in San Francisco, CA, USA See also: UW-Madison scientists also guide human skin cells to embryonic like state Turning Adult Cells Embryonic How to Make Stem Cells Stay Growing ......... 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For more on stem cells and cloning, go to CellNEWS at http://www.geocities.com/giantfideli/index.html

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