Stem cell side show

Before scientists can harness heart stem cells to repair damage to the organ, they have to pin down the elusive cells. On page 329, Oyama et al. bolster the case for a group of cells known as side population cells, showing for the first time that they home in on injured heart muscle and differentiate into all the types of cardiac cells in vivo.

Previous research has turned up several candidates for cardiac stem cells, including the side population cells. In the bone marrow, side population cells function as stem cells. The situation in the heart wasn't clear, however. If they are grown with heart muscle cells in vitro, cardiac side population (CSP) cells can specialize into heart muscle. However, researchers didn't know what stimulates the cells to differentiate or what they're capable of in...