Brain cells already do a lot, from memorizing equations to providing the information needed to navigate a crowded room. But a report in this week's issue of Science suggests that they can even perform the tasks of a completely different tissue.
Angelo Vescovi, a neurobiologist at the National Neurological Institute Carlo Besta in Milan, Italy, and his colleagues report that neural stem cells, which give rise to the three main types of brain cells, can become blood cells when transplanted into mice whose own blood-forming tissue, the bone marrow, has been mostly destroyed. The result provides a strong push to find other stem cell types with similar capabilities. And it opens the possibility of using neural stem cell transplants to treat human blood cell disorders such as aplastic anemia and severe combined immunodeficiency--an appealing idea, as bone marrow stem cells don't replenish themselves well in lab cultures. "What's interesting is the idea that cells can shake their fates," says Ron McKay, a neurobiologist at the National Institute of Neurological Disorders and Stroke in Bethesda, Maryland.
To understand better how that occurs, the team isolated neural stem cells from adult and embryonic mice and grew them singly in lab cultures. After irradiating mice to kill most of their bone marrow cells and create a vacancy that new cells might occupy, the researchers injected the neural stem cells into the animals. Because the donor mouse cells carried distinctive genetic markers, the researchers could trace their fate in the injected animals. Five months later, the investigators found that the blood of the recipients contained cells that not only displayed the donor cell marker protein but also produced proteins that only mature blood cells make. They also showed that the animals' bone marrow carried immature blood precursor cells that were descended from the neural cells.
No one knows exactly what caused the neural cells to turn into blood cells. But Vescovi and his colleagues suspect that the neural cells might be responding to the same signals that normally stimulate the few remaining blood stem cells to reproduce and mature after irradiation wipes out most of the bone marrow. "The result suggests that there's something quite powerful in the mature adult blood system that can instruct cells from a different origin what to do," says Arturo Alvarez-Buylla, a neurobiologist at The Rockefeller University in New York City.