Cell biology. Stem cells: new excitement, persistent questions

On pages 1775 and 1779, independent research teams describe experiments in which bone marrow cells became neuronlike cells in the brain, providing new evidence for the versatility of adult stem cells. But ample uncertainties must be resolved before such results can be translated into therapeutics. The most important next step, say several stem cell researchers, is to identify the molecular processes that underlie the impressive feats of stem cells, as many of the purported breakthroughs are simply observations.