This cover art depicts an undifferentiated pluripotent stem cell driving towards its goal to become a primary hepatocyte (a liver cell). The three lanes of the road symbolize the various conditions in which the liver hepatocyte can reach its destination. The GPS shows the best route, turning towards THRB, symbolic of the authors’ efforts to promote THRB enrichment in stem cells in order to achieve differentiation as a primary hepatocyte. This illustration was done in collaboration with Dr. Haiting Ma and Dr. Rudolf Jaenisch at the Whitehead Institute for Biomedical Resarch.