THE STORY OF IPS CELLS

Until fairly recently, 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 a different cell type.

However, in 2007, scientists were able to turn 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 also noticed that a small number of genes were active only in stem cells, and not in differentiated cells. Scientists in Japan wanted to see if introducing these genes back into differentiated cells could make them behave more like stem cells.

By introducing a cocktail of 24 different genes, the scientists were able to convert differentiated cells into stem cells. They gradually eliminated genes from the mixture, and in the end they were able to turn differentiated cells into stem cells by activating just 4 genes. These genes appear to be remodeling the cells' DNA, unlocking the genes that were shut down during differentiation.

Armed with the ability to reverse the differentiation process, scientist are exploring new ways to use stem cells in research and medicine.