The researchers said the finding suggests that converting bone marrow cells into brain neurons may be part of a previously unknown natural healing action the body uses to replace failed brain cells. Dr. Eva Mezey of the National Institute of Neurological Disorders and Stroke, first author of the other study in Science, agreed that the researchers may have found a way the body replaces neurons. She said there's no awareness of the repair because the process replaces a neuron as soon as the cell fails. This process could be similar to the way the body constantly replaces dead skin cells with new cells, she said. The studies are the latest in a hot new field of research exploring the ability of adult stem cells to transform themselves into other types of cells and to fill new roles in the body.
Bone marrow consists of at least two types of stem cells.
Earlier studies have shown these cells can convert themselves into muscle, bone and liver. There also have been studies showing that neural stem cells can convert into muscle or make a variety of brain cells. In Blau's study at Stanford, researchers obtained bone marrow from a strain of mice that carry in each cell a protein that glows in the dark. This bone marrow was injected into the tail vein of mice whose natural bone marrow had been killed by radiation. Later, the mice were killed and their brains examined.