Reversing Cell Differentiation
Until fairly recently, cell differentiation was seen as final and irreversible. Once a cell became specialized, it was referred to as "terminally differentiated." It was considered locked-in and unable to become any other cell type.
However, in 2006, scientists reported that they had turned a differentiated cell back into a stem cell with the potential to become any type of cell in the body.
The difference between a stem cell and a differentiated cell is reflected in the cells' DNA. In a stem cell, the DNA is arranged loosely, with its genes ready to spring into action. As signals enter the cell and differentiation begins, genes that will not be needed are shut down, and genes that will be required for a specialized function remain open and active.
Scientists noticed a small number of genes that were active only in stem cells and not in differentiated cells. Introducing just 4 of these genes back into differentiated cells made them behave like stem cells. The genes appear to be remodeling the cells' DNA, unlocking the genes that were shut down during differentiation.
The scientists named these cells "induced pluripotent stem cells," or iPS cells. In 2012, they won the Nobel Prize in Physiology or Medicine for their work.
In 2014, a group of scientists announced that they had turned differentiated cells back into stem cells simply by stressing them. This surprisingly simple process quickly and efficiently generates stem cells without using any kind of genetic manipulation.
Scientists think that stressing the cells—by dipping them in a slightly acidic solution or squeezing them through a tube—may activate genes that remodel the cells' DNA. Reverting to a more stem-like state may be something that cells do as a natural step in healing injured tissue.
Remarkably, STAP cells can give rise not only to any type of cell in the body, but also to cells in the placenta—something that neither embryonic cells nor iPS cells can do.
Armed with the ability to reverse the differentiation process, scientists are exploring new ways to use stem cells in research and medicine.
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Takahashi, K. & Yamanaka, S. (2006). Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell, 126(4), 663-676.
Thomson, H. (2014). Stem cell power unleashed after 30 minute dip in acid. New Scientist, 2954, 6-8.