Planarian Pluripotency

Many animals can regenerate tails, but few can regenerate heads, and how they do so is a fascinating problem. Tiny flatworms called planaria have long been famous for the ability to regenerate body parts (1–3) and as such, they are a valuable model system for elucidating mechanisms that control cell and tissue replacement, a process that is important for the survival of most organisms. On page 811 of this issue, Wagner et al. (4) examine the nature of the cells (called neoblasts) responsible for regeneration in planaria, and on page 852, Petersen and Reddien (5) reveal more about how the worm decides whether to regenerate a head or a tail.