mixed genes. The fused cells carry the chromosomes of the two cells of the marrow donor (pink) and resident liver cells (green).
Stem cells are advertised for their ability to develop into many types of tissue. But a year ago, researchers have been abuzz with two reports showing that some of these cells in the modified test tubes their identity by reprogramming to get into their new environment, but by merging with host cells ( Science , 15 March 02, p. 1989). Now two teams have developed the first evidence in animals that adult cells can transform a living fusion. The discovery suggests that it may be more difficult than the hope of developing therapies using adult stem cells.
Previous research has shown that stem cells from the bone marrow that normally form blood cells can generate new cells in the liver. When healthy mice marrow was injected into mice with liver disease whose own marrow had been eliminated, donor cells helped rebuild the damaged liver. This study, conducted by Eric Lagasse of Stem Cells Inc. in Palo Alto, California, and colleagues, was quoted among the best evidence for "transdifferentiation" - the ability of a cell type to be transformed into a another type when placed in a different environment.
But this change of identity may not have been real, according to a report in Nature online this week. Two teams - one led by Markus Grompe at Oregon Health and Science University in Portland and a separate group led by George Vassilopoulos, University of Washington, Seattle - found that the regenerated liver cells contain chromosomes host and donor cells. Thus, "the answer is very clear, they are made by fusion, not by differentiation," said Grompe. The nuclei of certain blood cells were reprogrammed as they fused the nuclei of liver cells, causing them to function as hepatocytes, he said.
scientists say that the clinical potential of adult stem cells is not necessarily diminished if the mechanism is melting. But it "makes the correction less upbeat disease" in view of the researcher on blood stem cells John Dick of the University of Toronto, because it could induce genomic instability and make the cells susceptible to cancer. As explained Grompe, "when you mix and match chromosomes, it is possible to become malignant. "
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