Wednesday, 21 November 2007

Reprogramming of human fibroblasts to ESCs achieved

Reprogramming of human fibroblasts to ESCs achieved Tuesday, 20 November 2007 Scientists have managed to reprogram human skin cells directly into cells that look and act like embryonic stem (ES) cells. The technique makes it possible to generate patient-specific stem cells to study or treat disease without using embryos or oocytes – and therefore could bypass the ethical debates that have plagued the field. The new discovery is being published online today in Cell, in a paper by Shinya Yamanaka of Kyoto University and the Gladstone Institute for Cardiovascular Disease in San Francisco, and in Science, in a paper by James Thomson and his colleagues at the University of Wisconsin. While both groups used just four genes to reprogram human skin cells, two of the four genes (Oct3/4, Sox2, c-Myc, and Klf4) used by the Japanese scientists were different from two of the four used by the American group (Oct4, Sox2, Nanog, and Lin28). All the genes in question, though, act in a similar way – they are master regulator genes whose role is to turn other genes on or off. A limitation is that the scientists use a retrovirus to insert the genes into the cells’ chromosomes. Retroviruses slip genes into chromosomes at random, and sometimes cause mutations that can make normal cells turn into cancers during this process. In addition, one of the genes that the Japanese scientists insert, the c-Myc gene, in fact is a cancer gene. “It is only a matter of time until retroviruses are not needed,” Dr. Douglas Melton, co-director of the Stem Cell Institute at Harvard University predicted. “Anyone who is going to suggest that this is just a side show and that it won’t work is wrong,” Dr. Melton said. The new discovery was preceded by work in mice. Last year, Dr. Yamanaka published a paper showing that he could add four genes to mouse cells and turn them into mouse embryonic stem cells (see Turning Adult Cells Embryonic). This publication last year set off what became an international race to repeat the work with human cells. “Dozens, if not hundreds of labs, have been attempting to do this,” said Dr. George Daley, associate director of the stem cell program at Children’s Hospital in Boston. In this new work, Yamanaka and his colleagues used a retrovirus to ferry into adult cells the same four genes they had previously employed to reprogram mouse cells: Oct3/4, Sox2, Klf4, and c-Myc. They reprogrammed cells taken from the facial skin of a 36-year-old woman and connective tissue from a 69-year-old man. Roughly one iPS (induced pluripotent stem) cell line was produced for every 5000 cells the researchers treated with the technique, an efficiency that enabled them to produce several cell lines from each experiment. Thomson's team started from scratch, identifying its own list of 14 candidate reprogramming genes. The team used a systematic process of elimination to identify four factors: Oct3 and Sox2, as Yamanaka used, and two different genes, Nanog and Lin28. The group reprogrammed cells from foetal skin and from the foreskin of a newborn boy. The researchers were able to transform about one in 10,000 cells, but still enough to create several cell lines from a single experiment. Although promising, both techniques share a downside. The retroviruses used to insert the genes could cause tumours in tissues grown from the cells. The crucial next step, everyone agrees, is to find a way to reprogram cells by switching on the genes rather than inserting new copies. The field is moving quickly toward that goal. "It is not hard to imagine a time when you could add small molecules that would tickle the same networks as these genes" and produce reprogrammed cells without genetic alterations, said Dr. Douglas Melton of Harvard University. Once the kinks are worked out, "the whole field is going to completely change," said stem cell researcher Jose Cibelli of Michigan State University in East Lansing. "People working on ethics will have to find something new to worry about." See also: UW-Madison scientists also guide human skin cells to embryonic like state Yamanaka Turns Human Fibroblasts to ESC-like Cells Turning Adult Cells Embryonic How to Make Stem Cells Stay Growing ......... ZenMaster

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