Our paper discusses an important step in the research surrounding stem cells.
Pluripotent stem cells are found in the early blastocyst, and can differentiate into different cell types such as neurons, cardiac muscle, or blood cells.
As is explained elsewhere on this paper, stem cells are extremely useful and hold amazing medical potential, especially to “grow” specific cells, tissues, and even organs for patients. Controversy mires the progress of stem cell research from embryos, however, and technical problems exist along with the ethical ones. Marius Wernig and his team of scientists have had success studying a way to get around this, however.
What if, instead of taking stem cells from newly created embryos, an individual’s own cells could be used? The cells in the adult body are no longer stem cells; they aren’t pluripotent, and can only be a certain type. But with special techniques, it’s actually possible to induce these adult cells to become stem cells, with a pluripotency that allows them to develop into whatever cell type is needed!
In this experiment, induced pluripotent stem cells were created using the fibroblast cells from mice. Fibroblasts were removed from underneath the skin of the subject mice. In order to revert the cell back to a induced pluripotent state, four specially selected transcription factors (Oct 4, Sox 2, c-Myc and Klf4) were used. These four transcription factors were each incorporated into the DNA of a virus that lacked the capacity to infect, and the fibroblasts were exposed to these viruses. Just like normal viruses, these injected their DNA into the fibroblast cells, and the DNA was incorporated into the cell. Now the fibroblasts contained the new transcription factors and produced proteins that the scientists wanted to test. As hoped, these proteins caused the fibroblasts to become induced pluripotent stem cells cells.
But how did the experimenters know if the cells that they had created were truly pluripotent stem cells? What could these cells form? First, a bit of background information must be included about chimeras. In basic terms, a chimera contains two sets of DNA, both of which are expressed. Different sections of the chimera’s body will be derived from different DNA. A good example is an individual with eyes of two different colors (one green, one blue, etc). Chimeras can be formed when two fertilized eggs fuse together at an early stage, or when an unfertilized egg or extra sperm fuses with a fertilized egg. Now the developing organism contains two different genetic codes. In most cases, chimeras are completely healthy. There is no worry of immune rejection, because the cells are joined together far before any immune system exists to reject either.
Now, back to the paper. How did chimeras help the scientists identify the pluripotent stem cells they had created? The scientists obtained mouse blastocysts that had certain...