Mitochondrial dynamics and cell fate Radial glia cells, the stem cells of early brain development, can generate more of themselves or generate differentiating neurons. Iwata et al. now show that these fate decisions involve the mitochondria. Cells that have fragmented mitochondria shortly after mitosis are more likely to become neurons, whereas cells that are undergoing mitochondrial fusion are likely to continue being stem cells. Science , this issue p. 858