Once a cell becomes committed to a particular fate, it shouldn't be able to become something else. However, a spate of recent work seems to have overturned this biological dogma. New findings offer the strongest evidence yet that certain cells can be steered onto new career paths. If the feat can be duplicated with human cells, it could lead to a new approach to treating Alzheimer's or other neurological diseases: Cells drawn from fetal tissue or even an adult patient might be reprogrammed to serve as replacement neurons.
The reprogrammed cells are rat oligodendrocyte precursor cells (OPCs), which scientists thought were irreversibly committed to becoming neuronal handmaidens called oligodendrocytes or astrocytes. After collecting OPCs from the optic nerves of newborn rats, Toru Kondo and Martin Raff of University College London used fetal calf serum or bone morphogenetic proteins to turn them into astrocyte-like cells. Then the scientists treated these astrocyte-like cells with basic fibroblast growth factor, a protein known to prompt proliferation of neural stem cells. The result? The astrocyte-like cells started dividing, producing what began to resemble neural stem cells. The scientists could then induce these cells to become neurons, astrocytes, and oligodendrocytes, they report in the 8 September issue of Science.
Previous reports that adult cells can be reprogrammed have been dogged by the question of whether immature cells hiding in the culture dishes gave rise to unexpected cell types. Because Kondo and Raff ran several experiments to test the purity of their well-characterized cells, they don't think the effect was due to undetected immature cells. The evidence that the OPCs' developmental clock can indeed be wound back is "totally convincing," says stem cell biologist Ben Barres of Stanford University.
Not to everyone, however. "It still remains possible that there are undetected multipotent stem cells that exist within the culture," says neuroscientist Fred Gage of the Salk Institute for Biological Studies in La Jolla, California. Also unclear is what the finding will mean for researchers who study brain development and repair, notes Sean Morrison of the University of Michigan, Ann Arbor. But if other elixirs can be discovered for various cell types, then more degenerative diseases might fall victim to newfound fountains of youth.
Related sites
Home page of Martin Raff, University College London
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