Coordination of progenitor specification and growth in mouse and chick spinal cord

Differentiation rates regulate pool sizes Even though a basketball player is bigger than a gymnast, their neural tubes are organized in the same way. Studying chick and mouse embryos, Kicheva et al. show that rates of cell differentiation are key (see the Perspective by Pourquie). In a two-phase process, signaling sweeps through the neural tube early on to establish some aspects of cell fate, but later, pools of progenitor cells take on their own regulation. A progenitor that differentiates is no longer a progenitor, and thus the rate of differentiation determines the size of the progenitor pool. The relative sizes of progenitor pools shift as development progresses, to build the spinal cord so that everyone, large or small, has the right proportion of each component. Science , this issue p. 10.1126/science.1254927 ; see also p. 1565