One to six months later, when the researchers examined the brains of the mice, they were surprised to find GFP inside brain cells, meaning that these cells had originated from the bone marrow. What's more, these cells in the brain looked like nerve cells and were making proteins that nerve cells make. In other words, the transplanted cells were able to respond to signals in the brain that told them to change into brain cells. When examining the brains of the female mice, any cells containing a Y chromosome had to be from the donor cells. Indeed, cells containing Y chromosomes were found in the brain.
Much more work needs to be done.
They appear to be making proteins that nerve cells make, but this is not definite proof that these cells are acting as nerve cells. Most had short non-branching outgrowths, not the long extensions of mature neurons. The donor cells were injected into the the bloodstream, so the cells had a long road to reach the brain. These factors may include growth factors and tropic factors . For example, how does age of the recipient mouse and the radiation used to kill the host bone marrow cells affect signals that tell cells to migrate.